Wei Zhang

Magnonics is a research field that has gained an increasing interest in both the fundamental and applied sciences in recent years. This field aims to explore and functionalize collective spin excitations in magnetically ordered materials for modern information technologies, sensing applications, and advanced computational schemes. Spin waves, also known as magnons, carry spin angular momenta that allow for the transmission, storage, and processing of information without moving charges. In integrated circuits, magnons enable on-chip data processing at ultrahigh frequencies without the Joule heating, which currently limits clock frequencies in conventional data processors to a few GHz. Recent developments in the field indicate that functional magnonic building blocks for in-memory computation, neural networks, and Ising machines are within reach. At the same time, the miniaturization of magnonic …

Developing hybrid materials and structures for electromagnetic wave engineering has been a promising route towards novel functionalities and tunabilities which are found useful in many modern applications and perspectives in new quantum technologies. Despite its established success in engineering optical light and terahertz waves, the implementation of meta-resonators operating at the microwave band is still emerging, especially those that allow for on-chip integration and size miniaturization, which has turned out crucial to developing hybrid quantum systems at the microwave band. In this work, we present a microwave meta-resonator consisting of split-ring and and spiral resonators, and implement it to the investigation of photon-magnon coupling for hybrid magnonic applications. We observe broadened bandwidth to the split ring modes augmented by the additional spiral resonator, and, by coupling the modes to a magnetic sample, the resultant photon-magnon coupling can be significantly enhanced to more than ten-fold. Our work suggests that combinatorial, hybrid microwave resonators may be a promising approach towards future development and implementation of photon-magnon coupling in hybrid magnonic systems.

The discovery of atomic monolayer magnetic materials has stimulated intense research activities in the two-dimensional (2D) van der Waals (vdW) materials community. The field is growing rapidly and there has been a large class of 2D vdW magnetic compounds with unique properties, which provides an ideal platform to study magnetism in the atomically thin limit. In parallel, based on tunneling magnetoresistance and magneto-optical effect in 2D vdW magnets and their heterostructures, emerging concepts of spintronic and optoelectronic applications such as spin tunnel field-effect transistors and spin-filtering devices are explored. While the magnetic ground state has been extensively investigated, reliable characterization and control of spin dynamics play a crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance (FMR) allows direct measurements of magnetic excitations, which provides …

Tunability of coherent coupling between fundamental excitations is an important prerequisite for expanding their functionality in hybrid quantum systems. In hybrid magnonics, the dipolar interaction between magnon and photon usually persists and cannot be switched off. Here, we demonstrate this capability by coupling a superconducting resonator to a layered hybrid perovskite antiferromagnet, which exhibits a magnon band gap due to its intrinsic Dzyaloshinskii-Moriya interaction. The pronounced temperature sensitivity of the magnon band gap location allows us to set the photon mode within the gap and to disable magnon-photon hybridization. When the resonator mode falls into the magnon band gap, the resonator damping rate increases due to the nonzero coupling to the detuned magnon mode. This phenomena can be used to quantify the magnon band gap using an analytical model. Our work brings new opportunities in controlling coherent information processing with quantum properties in complex magnetic materials.

Recent years have seen a rapid development of spintronics in the area of spin caloritronics. In particular, the spin Seebeck effect (SSE) has been observed in a diverse class of magnetic materials. In this talk, I will focus on our recent work on the investigation of SSE in the antiferromagntic Cr 2 O 3. We found that the SSE is sensitive to the orientation of the sublattice magnetization of Cr 2 O 3. This was identified by a unique angular dependence of the SSE signal while the sample is rotated relative an external magnetic field. By taking the measurement in the temperature range where the thermal excitation energy is less than the magnetic anisotropy energy, we observed a suppression of the SSE signal. This phenomenon indicates that the SSE signal is mainly contributed by magnons in the bulk Cr 2 O 3. We found that the spin-flop transition in our thin-film Cr 2 O 3 can be clearly measured as an abrupt jump and non …

Nonreciprocal magnon propagation has recently become a highly potential approach of developing chip-embedded microwave isolators for advanced information processing. However, it is challenging to achieve large nonreciprocity in miniaturized magnetic thin-film devices because of the difficulty of distinguishing propagating surface spin waves along the opposite directions when the film thickness is small. In this work, we experimentally realize unidirectional microwave transduction with sub-micrometer-wavelength propagating magnons in a yttrium iron garnet (YIG) thin-film delay line. We achieve a non-decaying isolation of 30 dB with a broad field-tunable bandpass frequency range up to 14 GHz. The large isolation is due to the selection of chiral magnetostatic surface spin waves with the Oersted field generated from the coplanar waveguide antenna. Increasing the geometry ratio between the antenna width …

Hybrid magnonic systems are a newcomer for pursuing coherent information processing owing to their rich quantum engineering functionalities. One prototypical example is hybrid magnonics in antiferromagnets with an easy-plane anisotropy that resembles a quantum-mechanically mixed two-level spin system through the coupling of acoustic and optical magnons. Generally, the coupling between these orthogonal modes is forbidden due to their opposite parity. Here we show that the Dzyaloshinskii–Moriya-Interaction (DMI), a chiral antisymmetric interaction that occurs in magnetic systems with low symmetry, can lift this restriction. We report that layered hybrid perovskite antiferromagnets with an interlayer DMI can lead to a strong intrinsic magnon-magnon coupling strength up to 0.24 GHz, which is four times greater than the dissipation rates of the acoustic/optical modes. Our work shows that the DMI in these …

Magnons possess nonreciprocity with multiply mechanisms and can reach ultra-small wavelength down to nanometer scale at microwave frequency excitations, they can be utilized for developing miniaturized and chip-embedded microwave isolation components for advanced information processing. Up to now, high performance of magnon isolation in magnetic thin-film devices is still demanding for practical applications. In this work, we experimentally realized broad-band nonreciprocal magnon propagation in a 100-nm yttrium iron garnet (YIG) thin film transducer. With nanofabrication of nanoscale (down to 200 nm) microwave antennas on fabricated YIG thin film (100 nm) device, we successfully demonstrate electrical detection of nonreciprocal short-wavelength (800 nm) spin wave propagation with 30 dB isolation, which is due to chirality selection of the Oersted field from the GSG antenna. Time-domain …

The opto-electronic oscillators hosting self-sustained oscillations by a time-delayed mechanism are of particular interest in long-haul signal transmission and processing. On the other hand, owing to their unique tunability and compatibility, magnons - as elementary excitations of spin waves - are advantageous carriers for coherent signal transduction across different platforms (either classical or quantum). In this work, we integrated an opto-electronic oscillator with a magnonic oscillator consisting of a microwave waveguide and a yttrium iron garnet sphere. The coherent coupling, hybridization, and the back action between the oscillator's photon mode and the magnon mode were observed. Leveraging the mature fiber-optic technologies in optoelectronics, this work lays out a new, hybrid platform for investigating long-distance coupling and nonlinearity in coherent magnonic phoenomena.

The richness in both the dispersion and energy of antiferromagnetic magnons has spurred the magnetism community to consider antiferromagnets for future spintronic/magnonic applications. However, the excitation and control of antiferromagnetic magnons remains challenging, especially when compared to ferromagnetic counterparts. A middle ground is found with synthetic antiferromagnet metamaterials, where acoustic and optical magnons exist at GHz frequencies. In these materials, the magnon energy spectrum can be tuned by static symmetry-breaking external fields or dipolar interactions hybridizing optical and acoustic magnon branches. Here, we experimentally measure the magnon energy spectrum of synthetic antiferromagnetic tetralayers, and discover avoided energy level crossings in the energy spectrum that are unexplained by the antiferromagnetic interlayer coupling. We explain our experimental results using a phenomenological model incorporating both fieldlike and dampinglike torques generated by spin pumping in noncollinear magnetic multilayers separated by normal-metal spacers. We show that an asymmetry in the fieldlike torques acting on different magnetic layers can lift the spectral degeneracies of acoustic and optical magnon branches and yield symmetry-breaking induced magnon-magnon interactions. Our work extends the phenomenology of spin pumping to noncollinear magnetization configurations and significantly expands ways of engineering magnon-magnon interactions within antiferromagnets and quantum hybrid magnonic materials.

Coherent interactions between different magnetic excitations can lead to formation of magnon band gaps and hybrid magnon modes, which can find their applications in magnonic devices and coherent information processing. In this work, we probe the intrinsic magnon band gap of a layered hybrid perovskite antiferromagnet by its strong coupling to a superconducting resonator. The pronounced temperature tunability of the magnon band gap location allows us to set the photon mode within the gap, leading to a reduction of effective magnon-photon coupling and eventually the disappearance of magnon-photon hybridization. When the resonator mode falls into the magnon band gap, the resonator damping rate increases due to the nonzero coupling to the detuned magnon mode. This allows for quantification of the magnon band gap using an analytical model. Our work brings new opportunities in controlling …

Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the central interests in spintronics applications. Here we report a giant Gilbert damping anisotropy in epitaxial Co50Fe50 (CoFe) thin film with a maximum-minimum damping ratio of 400 %, determined by broadband spin-torque as well as inductive ferromagnetic resonance (FMR). Our CoFe films are deposited via molecular beam epitaxy at room temperature. The films are then fabricated into micron-scale devices. The first sample series, with CoFe(10 nm) and CoFe(10 nm)/Pt(6 nm), are prepared for spin-torque FMR. The second sample series, with CoFe(20 nm), are prepared for vector network analyzer FMR measurements. In addition to the fourfold magnetocrystalline anisotropy, we also find a large fourfold Gilbert damping anisotropy, along with small and consistent inhomogeneous linewidth broadening. In order to exclude the two-magnon …

The discovery of atomic monolayer magnetic materials has stimulated intense research activities in the two-dimensional (2D) van der Waals (vdW) materials community. The field is growing rapidly and there has been a large class of 2D vdW magnetic compounds with unique properties, which provides an ideal platform to study magnetism in the atomically thin limit. While the magnetic ground state has been extensively investigated, reliable characterization and control of spin dynamics play a crucial role in designing ultrafast spintronic devices. Ferromagnetic resonance (FMR) allows direct measurements of magnetic excitations, which provides insight into the key parameters of magnetic properties such as exchange interaction, magnetic anisotropy, gyromagnetic ratio, spin-orbit coupling, damping rate, and domain structure. In our review article, we present an overview of the essential progress in probing spin …

Hybrid magnonic systems host a variety of characteristic phenomena such as the magnetically induced transparency (MIT) and Purcell effect, which are considered useful for future coherent quantum-information processing. In this work, we experimentally demonstrate a tunable MIT effect in the Y 3 Fe 5 O 12 (YIG)/Permalloy (Py) magnon-magnon coupled system via changing the magnetic field orientations. By probing the magneto-optic effects of Py and YIG thin films, we identify clear features of MIT spectra induced by the mode hybridization between the uniform mode of Py and the perpendicular standing spin-wave modes of YIG. By changing the external magnetic field orientations, we observe a tunable coupling strength between the YIG’s spin-wave modes and the Py’s uniform mode, upon the application of an out-of-plane magnetic field. This observation is theoretically interpreted by a geometrical …

The magneto-optic probing of hybrid magnonic systems is made possible due to a magnon's ability to couple with many quasiparticles, including photons and phonons. Several characteristic quantum phenomena are seen in these hybrid magnonic systems, including the magnetically-induced transparency (MIT) and Purcell effect [1, 2]. In this experiment, we magneto-optically detect features of MIT spectra induced by the mode hybridization of Py's ferromagnetic resonance and YIG's perpendicular standing spin-wave. Additionally, we demonstrate the possible tuning of this effect through manipulation of an external magnetic field's orientation and intensity. Our findings show high promise for investigating tunable coherent phenomena with hybrid magnonic platforms.

Antiferromagnets possess many potential applications due to their high-frequency dynamic properties. Here, we study combinations of ferromagnetic layers separated by non-magnetic layers of suitable thicknesses. These structures have an antiferromagnetic coupling between adjacent ferromagnetic layers and are called synthetic antiferromagnets. Synthetic antiferromagnets are useful materials for tuning magnon frequencies by manipulating magnon-magnon interactions. In this work, we consider Permalloy-Ru tetralayer structures. We previously predicted that tetralayers contain self-hybridization effect amongst acoustic or optical magnon pairs. We have now experimentally observed self-hybridization effects that are in close agreement with both macrospin model calculations and micromagnetic simulations. This work paves the way for electric tunability of magnon-magnon interactions.

We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon insulator. The results show that the thermal evolution of the Landé g factor (g) is anisotropic: gin-plane decreases while gout-of-plane increases with increasing temperature T. Moreover, the anisotropy of the g factor (Δg) and the anisotropy of saturation magnetization (ΔMs) are correlated below 4 K, but they diverge above 4 K. We show that the electronic orbital moment contributes to the g anisotropy at lower T, while the topological orbital moment induced by thermally excited spin chirality dictates the g anisotropy at higher T. Our work suggests an interplay among topology, spin chirality, and orbital magnetism in Cu(1,3-bdc).

Low dimensional magnetism reported in Van der Waals (VdW) materials has sparked a renewed interest in spintronic applications in recent years, focusing on two dimensional spin waves and antiferromagnetic magnon generation. We investigate Cu-based hybrid organic-inorganic perovskites which represent an intriguing class of quasi two-dimensional layered materials, with far greater chemical (and magnetic) variability than their VdW counterparts, making them potentially suited for spintronic applications. Here we examine the static and dynamic magnetic properties of (C 6 H 5 CH 3 CH 2 NH 3) 2 CuCl 4,(CH 3 CH 2 NH 3) 2 CuCl 4, and (C 6 H 5 CH 3 CH 2 NH 3) 2 CuBr 4 single crystals using SQUID magnetometry and ferromagnetic resonance (FMR) spectroscopy, respectively. Static magnetization and susceptibility measurements reveal the effects of organic cation and halide substitution on critical ordering …

Recent research on hybrid magnonics has been restricted by the long magnon wavelengths of the ferromagnetic resonance modes. We present an experiment on the hybridization of 250-nm-wavelength magnons with microwave photons in a multimode magnonic system consisting of a planar cavity and a magnetic bilayer. The coupling between magnon modes in the two magnetic layers, ie, the uniform mode in Permalloy and the perpendicular standing spin waves (PSSWs) in yttrium iron garnet, serves as an effective means for exciting short-wavelength PSSWs, which is further hybridized with the photon mode of the microwave resonator. The demonstrated magnon-photon coupling approaches the superstrong coupling regime, and can even be achieved near zero bias field.

Spin–orbit torque (SOT) is an emerging technology that enables the efficient manipulation of spintronic devices. The initial processes of interest in SOTs involved electric fields, spin–orbit coupling, conduction electron spins, and magnetization. More recently, interest has grown to include a variety of other processes that include phonons, magnons, or heat. Over the past decade, many materials have been explored to achieve a larger SOT efficiency. Recently, holistic design to maximize the performance of SOT devices has extended material research from a nonmagnetic layer to a magnetic layer. The rapid development of SOT has spurred a variety of SOT-based applications. In this article, we first review the theories of SOTs by introducing the various mechanisms thought to generate or control SOTs, such as the spin Hall effect, the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients, magnons, and …

Two-dimensional (2D) magnetic van der Waals crystals have received great attentions recently owing to their novel electronic and magnetic properties and rich potentials for low-dimensional and high-density spintronic devices. We investigated the magnetization dynamics of CrI3 and CrBr3 bulk single crystals by utilizing broadband ferromagnetic resonance (FMR) in a frequency range of 1 – 40 GHz and over a wide temperature range of 10 – 300 K. Complex features observed in the FMR spectra are quantitatively described by the multi-domain FMR theory. The minimum resonance frequency fmin in FMR spectra was recognized and analyzed as characteristics of the transition of the domain structure. Micromagnetic simulation on the domain structure and spin dynamics explains that the multi-domain structure exists under strong in-plane magnetic field for CrI3 and CrBr3 and significantly influences the magnetic …

Detection of phonons is critical for research on the interconversion between resonantly coupled magnons and phonons. Here we report the direct visualization of the resonant coupling of magnons and phonons by microfocused Brillouin light scattering on the Ni/Li Nb O 3 hybrid heterostructure. The static patterns of surface acoustic wave phonons, originating from the interference between the incident wave ψ 0 (A 0, k, φ 0) and reflected wave ψ 1 (A 1,− k, φ 1), can be modulated by magnetic field due to the magnon-phonon coupling. By analyzing the information of phonons obtained from Brillouin spectroscopy, the properties of the magnon system (Ni film), eg, ferromagnetic resonance field and resonance linewidth, can be determined. The results provide spatially resolved information about phonon manipulation and detection in a coupled magnon-phonon system.

Van der Waals magnets are uniquely positioned at the intersection between two-dimensional materials, antiferromagnetic spintronics, and magnonics. The interlayer exchange interaction in these materials enables antiferromagnetic resonances to be accessed at gigahertz frequencies. Consequently, these layered antiferromagnets are intriguing materials out of which quantum hybrid magnonic devices can be fashioned. Here, we use both a modified macrospin model and micromagnetic simulations to demonstrate a comprehensive antiferromagnetic resonance spectra in van der Waals magnets near the ultrathin (monolayer) limit. The number of optical and acoustic magnon modes, as well as the mode frequencies, are found to be exquisitely sensitive to the number of layers. We discover a self-hybridization effect where pairs of either optical or acoustic magnons are found to interact and self-hybridize through the …

The perpendicular shape anisotropy-spin transfer torque-magnetic random access memories (PSA-STT-MRAMs) take advantage of the nanopillar free-layer geometry for securing a good thermal stability factor from the shape anisotropy of the nanomagnet. Such a concept is particularly well-suited for small junctions down to a few nanometers. At such a volume size, the nanopillar can be effectively modeled as a Stoner–Wohlfarth particle, and the shape anisotropy scales with the spontaneous magnetization by∼ M s 2⁠. For almost all ferromagnets, M s is a strong function of temperature; therefore, the temperature-dependent shape anisotropy is an important factor to be considered in any modeling of the temperature-dependent performance of PSA-STT-MRAMs. In this work, we summarize and discuss various possible temperature-dependent contributions to the thermal stability factor and coercivity of the PSA-STT …

We measured spin Seebeck signals at the top and bottom surfaces of an antiferromagnetic Cr 2 O 3 film, using a Pt/Cr 2 O 3/Pt trilayer. Our experimental data, combined with micromagnetic simulations, clearly demonstrate that the uncompensated sublattice at the top and bottom surfaces plays a decisive role in determining the symmetry of the spin Seebeck signals, providing fundamental insight for understanding the generation of spin Seebeck signal in antiferromagnetic materials.

The interaction between magnetic and acoustic excitations has recently inspired many interdisciplinary studies ranging from fundamental physics to circuit implementation. Specifically, the exploration of their coherent interconversion enabled via the magnetoelastic coupling opens a new playground combining straintronics and spintronics and provides a unique platform for building up on-chip coherent information processing networks with miniaturized magnonic and acoustic devices. In this Perspective, we will focus on the recent progress of magnon–phonon coupled dynamic systems, including materials, circuits, imaging, and new physics. In particular, we highlight the unique features such as nonreciprocal acoustic wave propagation and strong coupling between magnons and phonons in magnetic thin-film systems, which provide a platform for their coherent manipulation and transduction. We will also review the …

Synthetic antiferromagnets (S-AFMs) have recently been suggested as ideal macroscopic systems to search for Exceptional Points (EPs). Both optical and acoustic modes exist within S-AFM structures. Within S-AFMs, dipolar interactions and symmetry-breaking external fields can hybridize acoustic and optical magnons. Physically, an EP is the point at which the optical and acoustic modes coalesce and are indistinguishable from one another. Beyond this, only a single magnon branch exists. This implies that there is no magnon-magnon interaction. In this work, we calculate EPs in S-AFMs using micromagnetic simulations. We have determined that adjusting the saturation magnetization leads to a shift in the EP location. This suggests that dipolar interactions play a much larger role than previously considered. The results indicate an opportunity for simulation-supported experimental strategies to use EPs for magnon …

We demonstrate the electrical detection of magnon–magnon hybrid dynamics in yttrium iron garnet/Permalloy (YIG/Py) thin film bilayer devices. Direct microwave current injection through the conductive Py layer excites the hybrid dynamics consisting of the uniform mode of Py and the first standing spin wave (n= 1) mode of YIG, which are coupled via interfacial exchange. Both the two hybrid modes, with Py-or YIG-dominated excitations, can be detected via the spin rectification signals from the conductive Py layer, providing phase resolution of the coupled dynamics. The phase characterization is also applied to a nonlocally excited Py device, revealing the additional phase shift due to the perpendicular Oersted field. Our results provide a device platform for exploring hybrid magnonic dynamics and probing their phases, which are crucial for implementing coherent information processing with magnon excitations.

Antiferromagnetic (AFM) spin-orbit torque oscillators are important due to potential applications ranging from magnetic random-access memory to THz emitters. However, AFM spin-torque oscillators operate in the THz-range, and direct observation of THz magnetization dynamics is difficult. Previously, in ferromagnetic spin-torque oscillators, current-induced unidirectional magnetoresistance (UMR) signals accompanied the emission of microwave radiation at the ferromagnetic resonance frequency [1, 2], which implies that observations of UMR may provide indirect evidence of AFM-resonance. Here we present transport results on magnetron sputtered AFM FeRh/Pt films, fabricated into nanowire geometries. A current-induced UMR is observed, in addition to anisotropic magnetoresistance effects. These findings suggest a route toward designing AFM spin-orbit torque oscillators.

Within both synthetic ferromagnets and antiferromagnets, exceptional points, where optical and acoustic magnons coalesce into a single branch, can be used to control the magnon energy spectra. To date, exceptional point phenomena in magnon systems have been predominantly predicted and understood within the framework of macrospin models that are based upon coupled Landau–Lifshitz–Gilbert equations of motion. Although these equations can be readily linearized and solved, they do not necessarily incorporate all of the physical effects that are present in a real synthetic magnetic structure such as dipolar interactions. We have used micromagnetic simulations to model Permalloy based synthetic magnets that include both dipolar interactions, as well as the interlayer exchange coupling which determines whether or not the material is ferromagnetic or antiferromagnetic. For the material parameters …

Next-generation terahertz (THz) sources demand lightweight, low-cost, defect-tolerant, and robust components with synergistic, tunable capabilities. However, a paucity of materials systems simultaneously possessing these desirable attributes and functionalities has made device realization difficult. Here we report the observation of asymmetric spintronic-THz radiation in Two-Dimensional Hybrid Metal Halides (2D-HMH) interfaced with a ferromagnetic metal, produced by ultrafast spin current under femtosecond laser excitation. The generated THz radiation exhibits an asymmetric intensity toward forward and backward emission direction whose directionality can be mutually controlled by the direction of applied magnetic field and linear polarization of the laser pulse. Our work demonstrates the capability for the coherent control of THz emission from 2D-HMHs, enabling their promising applications on the ultrafast …

Quantum technology has made tremendous strides over the past two decades with remarkable advances in materials engineering, circuit design, and dynamic operation. In particular, the integration of different quantum modules has benefited from hybrid quantum systems, which provide an important pathway for harnessing different natural advantages of complementary quantum systems and for engineering new functionalities. This review article focuses on the current frontiers with respect to utilizing magnons for novel quantum functionalities. Magnons are the fundamental excitations of magnetically ordered solid-state materials and provide great tunability and flexibility for interacting with various quantum modules for integration in diverse quantum systems. The concomitant-rich variety of physics and material selection enable exploration of novel quantum phenomena in materials science and engineering. In …

B63. 00008: Spintronic Terahertz Emission by Ultrafast Spin-Charge Current Conversion in Reduced Dimensional Organic-Inorganic Hybrid Perovskites*AbstractPresenter:Eric Vetter(Physics, North Carolina State University)Authors:Kankan Cong(Advanced Photon Source, Argonne National Laboratory)Eric Vetter(Physics, North Carolina State University)Yan Liang(Department of Chemistry, University of North Carolina at Chapel Hill)Yi Li(Department of Physics, Oakland University)Qi Zhang(Advanced Photon Source, Argonne National Laboratory)Yuzan Xiong(Department of Physics, Oakland University)Hongwei Qu(Department of Electronic and Computer Engineering, Oakland University)Richard D Schaller(Advanced Photon Source, Argonne National Laboratory)Axel Hoffmann(Materials Science Division, Argonne National Laboratory)Alexander F Kemper(Physics, North Carolina State University)Wei You …

S47. 00001: Topological Insulator/Magnetic Insulating Oxide: A Platform for Efficient Spin Current Transport*AbstractPresenter:Peng Li(Auburn University)Authors:Peng Li(Auburn University)Steven S-L Zhang(case western reserve university)Lauren Riddiford(Stanford University)Timothy Pillsbury(Penn Sate University)Jinjun Ding(Colorado State University)James Kally(Penn Sate University)Alexander Grutter(National Institute of Standards and Technology)Gaurab Rimal(University of Wyoming)Chong Bi(Stanford University)Gyorgy Csaba(Pazmany Peter Catholic University)J Samuel Jiang(Argonne National Laboratory)Junjia Ding(Argonne National Laboratory)Wei Zhang(Oakland University)Jinke Tang(University of Wyoming)Weigang Wang(University of Arizona)Olle Heinonen(Argonne National Laboratory)Valentyn Novosad(Argonne National Laboratory)Axel Hoffmann(University of Illinois at Urbana-Champaign …

We demonstrate the magnetically-induced transparency (MIT) effect in YFeO(YIG)/Permalloy (Py) coupled bilayers. The measurement is achieved via a heterodyne detection of the coupled magnetization dynamics using a single wavelength that probes the magneto-optical Kerr and Faraday effects of Py and YIG, respectively. Clear features of the MIT effect are evident from the deeply modulated ferromagnetic resonance of Py due to the perpendicular-standing-spin-wave of YIG. We develop a phenomenological model that nicely reproduces the experimental results including the induced amplitude and phase evolution caused by the magnon–magnon coupling. Our work offers a new route towards studying phase-resolved spin dynamics and hybrid magnonic systems.

We report the construction and characterization of a comprehensive magnonic-opto-electronic oscillator (MOEO) system based on 1550-nm photonics and yttrium iron garnet (YIG) magnonics. The system exhibits a rich and synergistic parameter space because of the ability to control individual photonic, electronic, and magnonic components. Taking advantage of the spin wave dispersion of YIG, the frequency self-generation as well as the related nonlinear processes becomes sensitive to the external magnetic field. Besides being known as a band-pass filter and a delay element, the YIG delay line possesses spin wave modes that can be controlled to mix with the optoelectronic modes to generate higher-order harmonic beating modes. With the high sensitivity and external tunability, the MOEO system may find usefulness in sensing applications in magnetism and spintronics beyond optoelectronics and photonics.

Pure spin currents have been ubiquitous in contemporary spintronics research. Despite its profound physical and technological significance, the detection of pure spin current has largely remained indirect, which is usually achieved by probing spin-transfer torque effects or spin-to-charge conversions. By using scanning transmission x-ray microscopy, we report the direct detection and spatial mapping of spin accumulation in a nonmagnetic Cu layer without any direct charge current injection. Such a pure spin current is induced by spin pumping from a Ni 80 Fe 20 layer and is not accompanied by concomitant charge motion. The observed frequency dependence indicates that the signal is dominated by a coherent, pure spin current, but the magnitude of the spin accumulation suggests also possible additional thermal contributions. Our technique takes advantage of the x-ray magnetic circular dichroism and the …

The resonant coupling of phonons and magnons is important for the interconversion of phononic and spin degrees of freedom. We study the phonon transmission in Li Nb O 3 manipulated by the dynamic magnetization in a Ni thin film. It is observed that the phonons can be absorbed strongly through resonant magnon-phonon coupling, which is realized by our modifying the magnon-phonon coupling within the Ni itself as well as our optimizing the interfacial coupling between Ni and Li Nb O 3. The line shapes of phonon transmission are further investigated considering the magnon-phonon interconversion in the elastically driven ferromagnetic resonance process. The results promote unique routes for phonon manipulation and detection in the presence of magnetization dynamics.

Hybrid dynamic systems have recently gained interest with respect to both fundamental physics and device applications, particularly with their potential for coherent information processing. In this perspective, we will focus on the recent rapid developments of magnon-based hybrid systems, which seek to combine magnonic excitations with diverse excitations for transformative applications in devices, circuits, and information processing. Key to their promising potentials is that magnons are highly tunable excitations and can be easily engineered to couple with various dynamic media and platforms. The capability of reaching strong coupling with many different excitations has positioned magnons well for studying solid-state coherent dynamics and exploiting unique functionality. In addition, with their gigahertz frequency bandwidth and the ease of fabrication and miniaturization, magnonic devices and systems can be …

U42. 00005: Rotating Néel Order to Probe Crystalline and Non-Crystalline AMR in FeRh*AbstractPresenter:Joseph Sklenar(Wayne State Univ)Authors:Joseph Sklenar(Wayne State Univ)Soho Shim(University of Illinois Urbana-Champaign)HIlal Saglam(Argonne National Laboratory)Kisung Kang(University of Illinois Urbana-Champaign)Junseok Oh(University of Illinois Urbana-Champaign)Greg A Hamilton(University of Illinois Urbana-Champaign)Wei Zhang(Oakland University)Matthew Gilbert(University of Illinois Urbana-Champaign)Andre Schleife(University of Illinois Urbana-Champaign)Axel Hoffmann(University of Illinois Urbana-Champaign)Nadya Mason(University of Illinois Urbana-Champaign)Anisotropic magnetoresistance (AMR) effects are a promising starting point for the electrical readout of antiferromagnetic memory in a spintronic device. We characterized both crystalline and non-crystalline AMR in …

We demonstrate a voltage-controlled exchange bias effect in CoFeB/MgO/CoFeB magnetic tunnel junctions that is related to the interfacial Fe (Co) O x formed between the CoFeB electrodes and the MgO barrier. The unique combination of interfacial antiferromagnetism, giant tunneling magnetoresistance, and sharp switching of the perpendicularly magnetized CoFeB allows sensitive detection of the exchange bias. We find that the exchange bias field can be isothermally controlled by magnetic fields at low temperatures. More importantly, the exchange bias can also be effectively manipulated by the electric field applied to the MgO barrier due to the voltage-controlled antiferromagnetic anisotropy in this system.

The angular dependence of the microwave-driven spin rectification (SR) effect in single crystalline Co 0.5 Fe 0.5 alloy film is systematically investigated. Due to the strong current-orientation dependent anisotropic magnetoresistance (AMR), the SR effects in CoFe film strongly deviate from the ordinary sin 2φ M cos φ M relation with φ M defined as the magnetization angle away from the current. A giant Gilbert damping anisotropy in the CoFe film with a maximum–minimum ratio of 520% is observed, which can impose a strong anisotropy onto magnetic susceptibility. The observed unusual angular dependence can be well explained by the theory including current-orientation dependent AMR and anisotropic magnetic susceptibility. Our work also suggests that the strong current-orientation dependent AMR in single crystalline CoFe film could exist up to the gigahertz frequency range.

H71. 00388: Probing Chirality Induced Spin Selectivity in Chiral 2D Hybrid Perovskites Using Spin Hall Magnetoresistance*AbstractPresenter:Eric Vetter(Physics, North Carolina State University)Authors:Eric Vetter(Physics, North Carolina State University)Yan Liang(Department of Chemistry, University of North Carolina at Chapel Hill)Yuzan Xiong(Department of Physics, Oakland University)Shulei Zhang(Materials Science Division, Argonne National Laboratory)Zhizhi Zhang(Materials Science Division, Argonne National Laboratory)Yi Li(Department of Physics, Oakland University)Hongwei Qu(Department of Electronic and Computer Engineering, Oakland University)Valentyn Novosad(Materials Science Division, Argonne National Laboratory)Axel Hoffmann(Materials Science Division, Argonne National Laboratory)Wei You(Department of Chemistry, University of North Carolina at Chapel Hill)Wei Zhang(Department …

The longitudinal and transverse resistivities of single crystalline Fe(1 1 0) film are both experimentally studied as functions of the magnetization orientation and the current orientation with respect to the crystalline axes. Unusual dependences and symmetries are revealed but cannot be described well by established conventional models. Furthermore, the anisotropic magnetoresistance ratios differ by more than one order of magnitude for currents along different crystalline directions. Analytical expressions for the resistivities are derived by using a phenomenological model based on a series expansion of the resistivity tensor with respect to the direction cosines of the magnetization up to the fourth order. The experimental data can be fitted well by these expressions, and the resistivity coefficients obtained from the fitting are consistent with the symmetries of the current-direction dependence measurements. The …

Using first-principles transport calculations, we predict that the anisotropic magnetoresistance (AMR) of single-crystal Co x Fe 1− x alloys is strongly dependent on the current orientation and alloy concentration. An intrinsic mechanism for AMR is found to arise from the band crossing due to magnetization-dependent symmetry protection. These special k points can be shifted towards or away from the Fermi energy by varying the alloy composition and hence the exchange splitting, thus allowing AMR tunability. The prediction is confirmed by delicate transport measurements, which further reveal a reciprocal relationship of the longitudinal and transverse resistivities along different crystal axes.

Antiferromagnets with tunable phase transitions are promising for future spintronics applications. We investigated spin-dependent transport properties of FeRh thin films, which show a temperature driven antiferromagnetic-to-ferromagnetic phase transition. Epitaxial FeRh films grown on MgO (001) substrates exhibit a clear magnetic and electronic phase transition. By performing anomalous Hall and anomalous Nernst effect measurements over a wide range of temperatures, we demonstrate that the thermally driven transition shows distinctly different transverse transport on both side of the phase transition. Particularly, a sign change of both anomalous Hall and Nernst signals is observed.

H71. 00073: Optimizing the Lumped Element Resonator via changing the total capacitance and the coplanar waveguide distance for effective magnon-photon coupling*AbstractPresenter:Yuzan Xiong(Electronic and Computer Engineering, Oakland University)Authors:Yuzan Xiong(Electronic and Computer Engineering, Oakland University)Yi Li(Argonne National Laboratory)Tomas Polakovic(Argonne National Laboratory)Ralu Divan(Argonne National Laboratory)john pearson(Argonne National Laboratory)Hongwei Qu(Electronic and Computer Engineering, Oakland University)Zhili Xiao(Argonne National Laboratory)Wai-Kwong Kwok(Argonne National Laboratory)Wei Zhang(Electronic and Computer Engineering, Oakland University)Valentyn Novosad(Argonne National Laboratory)Controllable superconducting quantum circuits with strong coupling strength is a key ingredient in the study of magnon-photon …

We experimentally identify coherent spin pumping in the magnon-magnon hybrid modes of yttrium iron garnet/permalloy (YIG/Py) bilayers. By reducing the YIG and Py thicknesses, the strong interfacial exchange coupling leads to large avoided crossings between the uniform mode of Py and the spin wave modes of YIG enabling accurate determination of modification of the linewidths due to the dampinglike torque. We identify additional linewidth suppression and enhancement for the in-phase and out-of-phase hybrid modes, respectively, which can be interpreted as concerted dampinglike torque from spin pumping. Furthermore, varying the Py thickness shows that both the fieldlike and dampinglike couplings vary like 1/t Py, verifying the prediction by the coupled Landau-Lifshitz equations.

We demonstrate the detection of phase-resolved magnetization dynamics with combinatorial magneto-optic Kerr and Faraday effects. The method uses a continuous-wave laser that is amplitude-modulated at the spin dynamic frequencies and thus allows for coherent tracking of the spin dynamics, akin a “lock-in”-type measurement. In particular, our method, using a single 1550 nm wavelength, probes simultaneously the ferromagnetic (FM) resonance of Y 3 Fe 5 O 12 (YIG) and Permalloy (Py = Ni 80 Fe 20 ) in a YIG-Py heterostructure. The fiber-based magneto-optic components also have the advantage of being made into a compact, tabletop or even portable system with yet robust measurement performances. We believe that our method will be found useful in studying hybrid quantum magnonic systems and/or investigating phase-resolved spin dynamics in nanomagnet structures involving both FM insulators and …

Doping of two-dimensional (2D) semiconductors has been intensively studied toward modulating their electrical, optical, and magnetic properties. While ferromagnetic 2D semiconductors hold promise for future spintronics and valleytronics, the origin of ferromagnetism in 2D materials remains unclear. Here, we show that substitutional Fe-doping of MoS 2 and WS 2 monolayers induce different magnetic properties. The Fe-doped monolayers are directly synthesized via chemical vapor deposition. In both cases, Fe substitutional doping is successfully achieved, as confirmed using scanning transmission electron microscopy. While both Fe: MoS 2 and Fe: WS 2 show PL quenching and n-type doping, Fe dopants in WS 2 monolayers are found to assume deep-level trap states, in contrast to the case of Fe: MoS 2, where the states are found to be shallow. Using μm-and mm-precision local NV− magnetometry and …