We report measurement of a spin pumping effect due to fluctuations of the magnetic order of IrMn thin films. A precessing NiFe ferromagnet injected spins into IrMn spin sinks, and enhanced damping was observed around the IrMn magnetic phase transition. Our data was compared to a recently developed theory and converted into interfacial spin mixing conductance enhancements. By spotting the spin pumping peak, the thickness dependence of the IrMn critical temperature could be determined and the characteristic length for the spin-spin interactions was deduced.
We employ the recently discovered antiferromagnetic tunneling anisotropic magnetoresistance to study the behavior of antiferromagnetically ordered moments in IrMn exchange coupled to NiFe. Experiments performed by common laboratory tools for magnetization and electrical transport measurements allow us to directly link the broadening of the NiFe hysteresis loop and its shift (exchange bias) to the rotation and pinning of antiferromagnetic moments in IrMn. At higher temperatures, the broadened loops show zero shift which correlates with the observation of fully rotating antiferromagnetic moments…
Antiferromagnetic spintronics is an emerging field; antiferromagnets can improve the functionalities of ferromagnets with higher response times, and having the information shielded against external magnetic field. Moreover, a large list of aniferromagnetic semiconductors and metals with Néel temperatures above room temperature exists. In the present manuscript, we persevere in the quest for the limits of how large can anisotropic magnetoresistance be in antiferromagnetic materials with very large spin-orbit coupling. We selected IrMn as a prime example of first-class moment (Mn) and spin-orbit…
We investigate the impact of pinned antiferromagnetic order on the decoherence of spin current in polycrystalline IrMn. In NiFe/Cu/IrMn/CoFe multilayers, we coherently pump an electronic spin current from NiFe into IrMn, whose antiferromagnetic order is globally pinned by static exchange-bias coupling with CoFe. We observe no anisotropic spin decoherence with respect to the orientation of the pinned antiferromagnetic order. We also observe no difference in spin decoherence for samples with and without pinned antiferromagnetic order. Moreover, although there is a pronounced resonance linewidth …
Spin-transfer-torque, a transfer of angular momentum between the electron spin and the local magnetic moments, is a promising and key mechanism to control ferromagnetic materials in modern spintronic devices . However, much less attention has been paid to the same effect in antiferromagnets. For the sake of investigating how the spin current interacts with the magnetic moments in antiferromagnets, we perform spin-torque ferromagnetic resonance measurements on Co20Fe60B20 4nm/Ir25Mn75 tIrMn nm/Pt 4 nm multilayers under a spin Hall effect of Pt. The effective magnetic damping in Co20Fe60B20 is m…
We present a comprehensive study of the exchange bias effect in a model system. Through numerical analysis of the exchange bias and coercive fields as a function of the antiferromagnetic layer thickness we deduce the absolute value of the averaged anisotropy constant of the antiferromagnet. We show that the anisotropy of IrMn exhibits a finite size effect as a function of thickness. The interfacial spin disorder involved in the data analysis is further supported by the observation of the dual behavior of the interfacial uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry …
We provide a complete and systematic first-principles study of the thermodynamic stability, structural parameters, and magnetic properties of the T1 non-collinear antiferromagnetic L1$_2$-IrMn$_3$ surface and L1$_2$-IrMn$_3$/Fe heterostructure. Furthermore, we investigate the exchange-bias effect in the heterostructure and describe its previously unknown complex magnetic coupling at the interface. We consider four atomic configurations and four magnetic arrangements, finding two stable terminations for the surface and for the heterostructure, which are in good agreement with experimental HR-TE…
We report an investigation of temperature and IrMn layered thickness dependence of anomalous-Hall resistance (AHR), anisotropic magnetoresistance (AMR), and magnetization on Pt/Ir20Mn80/Y3Fe5O12 (Pt/IrMn/YIG) heterostructures. The magnitude of AHR is dramatically enhanced compared with Pt/YIG bilayers. The enhancement is much more profound at higher temperatures and peaks at the IrMn thickness of 3 nm. The observed spin-Hall magnetoresistance (SMR) in the temperature range of 10-300 K indicates that the spin current generated in the Pt layer can penetrate the entire thickness of the IrMn layer…
Antiferromagnetic spintronic devices have the potential to outperform conventional ferromagnetic devices due to their ultrafast dynamics and high data density. A challenge in designing these devices is the control and detection of the orientation of the anti-ferromagnet. One of the most promising ways to achieve this is through the exchange bias effect. This is of particular importance in large scale multigranular devices. Due to the large system sizes, previously, only micromagnetic simulations have been possible, these have an assumed distribution of antiferromagnetic anisotropy directions. …
Using an atomistic spin model, we have simulated spin wave injection and propagation into antiferromagnetic IrMn from an exchange coupled CoFe layer. The spectral characteristics of the exited spin waves have a complex beating behavior arising from the non-collinear nature of the antiferromagnetic order. We find that the frequency response of the system depends strongly on the strength and frequency of oscillating field excitations. We also find that the strength of excited spin waves strongly decays away from the interfacial layer with a frequency dependent attenuation. Our findings suggest t…
Manipulation of antiferromagnetic (AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. In spite of the electrical modulation of insulated AFMs through coupling between their intrinsic ferroelectricity and antiferromagnetism, direct electrical control of AFM metals remains challenging due to the screening effect by the surface charge, and the manipulation is confined to a limited depth of atomic dimensions, which is insufficient to form a stable AFM exchange spring. In the present letter we primarily report a reversible electrical control…
Anti-ferromagnetic materials have the possibility to offer ultra fast, high data density spintronic devices. A significant challenge is the reliable detection of the state of the antiferromagnet, which can be achieved using exchange bias. Here we develop an atomistic spin model of the athermal training effect, a well known phenomenon in exchange biased systems where the bias is significantly reduced after the first hysteresis cycle. We find that the setting process in granular thin films relies on the presence of interfacial mixing between the ferromagnetic and antiferromagnetic layers. We sys…
We investigated spin injection by spin pumping from a spin-injector(NiFe) into a spin-sink to detect spin fluctuations in the spin-sink. By scanning the ordering-temperature of several magnetic transitions, we found that enhanced spin pumping due to spin fluctuations applies with several ordering states: ferromagnetic(Tb) and antiferromagnetic(NiO, NiFeOx, BiFeO3, exchange-biased and unbiased IrMn). Results also represent systematic experimental investigation supporting that the effect is independent of the metallic and insulating nature of the spin-sink, and is observed whether the spin curre…
There has been considerable interest in spin-orbit torques for the purpose of manipulating the magnetization of ferromagnetic (FM) films or nano-elements for spintronic technologies. Spin-orbit torques are derived from spin currents created from charge currents in materials with significant spin-orbit coupling that diffuse into an adjacent FM material. There have been intensive efforts to search for candidate materials that exhibit large spin Hall angles, i.e. efficient charge to spin current conversion. Here we report, using spin torque ferromagnetic resonance, the observation of a giant spin…
Damping in magnetization dynamics characterizes the dissipation of magnetic energy and is essential for improving the performance of spintronics-based devices. While the damping of ferromagnets has been well studied and can be artificially controlled in practice, the damping parameters of antiferromagnetic materials are nevertheless little known for their physical mechanisms or numerical values. Here we calculate the damping parameters in antiferromagnetic dynamics using the generalized scattering theory of magnetization dissipation combined with the first-principles transport computation. For…
The exchange interaction determines the ferromagnetic (FM) or antiferromagnetic (AFM) ordering of atomic spins. When ferromagnets and antiferromagnets are coupled together, they often exhibit the exchange bias effect, a unidirectional interface exchange field causing a shift of the magnetic hysteresis loop. The effective magnitude of this interface exchange field is at most a few percent of the bulk exchange, arising from pinned interfacial spins in the antiferromagnet. The pinned spins are known to comprise a small fraction of the total number of interface spins, yet their exact nature and ph…
Tunneling junctions containing no ferromagnetic elements have been fabricated and we show that distinct resistance states can be set by field cooling the devices from above the Néel along different orientations. Variations of the resistance up to 10% are found upon field cooling in applied fields of 2T, in-plane or out of plane. Below TN, we found that the metastable states are insensitive to magnetic fields thus constituting a memory element robust against external magnetic fields. Our work provides the demonstration of an electrically readable magnetic memory device, which contains no ferrom…
In this work, IrMn$_{3}$/insulating-Y$_{3}$Fe$_{5}$O$_{12}$ exchange-biased bilayers are studied. The behavior of the net magnetic moment $Δm_{AFM}$ in the antiferromagnet is directly probed by anomalous and planar Hall effects, and anisotropic magnetoresistance. The $Δm_{AFM}$ is proved to come from the interfacial uncompensated magnetic moment. We demonstrate that the exchange bias and rotational hysteresis are induced by the irreversible switching of the $Δm_{AFM}$. In the training effect, the $Δm_{AFM}$ changes continuously. This work highlights the fundamental role of the $Δm_{AFM}$ in th…
We demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. In our study we use an electrical detection technique of the ferromagnetic resonance driven by an in-plane ac-current in a NiFe/IrMn bilayer. At room temperature, we observe antidamping-like spin torque acting on the NiFe ferromagnet, generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias…
We show how compensated antiferromagnetic spins can be implemented in the micromagnetic simulation program MuMax3. We demonstrate that we can model spin flop coupling as a uniaxial anisotropy for small canting angles and how we can take into account the exact energy terms for strong coupling between a ferromagnet and compensated antiferromagnet. We also investigate the training effect in biaxial antiferromagnets and reproduce the training effect in a polycrystalline IrMn/CoFe bilayer.
Heterostructures of Co-doped ZnO and Permalloy were investigated for their static and dynamic magnetic interaction. The highly Co-doped ZnO is paramagentic at room temperature and becomes an uncompensated antiferromagnet at low temperatures, showing a narrowly opened hysteresis and a vertical exchange bias shift even in the absence of any ferromagnetic layer. At low temperatures in combination with Permalloy an exchange bias is found causing a horizontal as well as vertical shift of the hysteresis of the heterostructure together with an increase in coercive field. Furthermore, an increase in t…
We study the anomalous Hall-like effect (AHLE) and the effective anisotropic magnetoresistance (EAMR) in antiferromagnetic γ -IrMn3/Y3Fe5O12(YIG) and Pt/YIG heterostructures. For γ -IrMn3/YIG, the EAMR and the AHLE resistivity change sign with temperature due to the competition between the spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE) induced by the interfacial antiferromagnetic uncompensated magnetic moment. In contrast, for Pt/YIG the AHLE resistivity changes sign with temperature whereas no sign change is observed in the EAMR. This is because the MPE and the SMR …
In spintronics applications, ultrafast spin dynamics have to be controlled at femtosecond (fs) timescales via fs-laser radiation. At such ultrafast timescales, the effect of the Gilbert damping factor α on ultrafast demagnetization time should be considered. In previous explorations for the relationship between these two parameters, it was found that the theoretical calculations based on the local spin-flip scattering model do not agree with the experimental results. Here, we find that in Fe81Ga19(FeGa)/Ir20Mn80(IrMn) bilayers, the unconventional IrMn thickness dependence of α results from the…
Using Y3Fe5O12 (YIG) thin films grown by our sputtering technique, we study dynamic spin transport in nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AF) materials by ferromagnetic resonance (FMR) spin pumping. From both inverse spin Hall effect (ISHE) and damping enhancement, we determine the spin mixing conductance and spin Hall angle in many metals. Surprisingly, we observe robust spin conduction in AF insulators excited by an adjacent YIG at resonance. This demonstrates that YIG spin pumping is a powerful and versatile tool for understanding spin Hall physics, spin-orbit coupli…
Antiferromagnetic (AFM) materials recently have shown interest in the research in spintronics due to its zero stray magnetic field, high anisotropy, and spin orbit coupling. In this context, the bi-metallic AFM Mn2Au has drawn attention because it exhibits unique properties and its Neel temperature is very high. Here, we report spin pumping and inverse spin Hall effect investigations in Mn2Au and CoFeB bilayer system using ferromagnetic resonance. We found large spin Hall angle θ_SH = 0.22
We report an alternative mechanism for the physical origin of the temperature-dependent ferromagnetic relaxation of Permalloy (NiFe) thin films. Through spin-pumping experiments, we demonstrate that the peak in the temperature-dependence of NiFe damping can be understood in terms of enhanced spin angular momentum absorption at the magnetic phase transition in antiferromagnetic surface-oxidized layers. These results suggest new avenues for the investigation of an incompletely-understood phenomenon in physics.
We report intrinsic spin decay length of an antiferromagnetic insulator. We found that at an antiferromagnetic/ferromagnetic interface, a spin current generated by spin pumping is strongly suppressed by two-magnon scattering. By eliminating the two-magnon contribution, we discovered that the characteristic length of spin decay in NiO changes by two-orders of magnitude through the paramagnetic to antiferromagnetic transition. The spin decay length in the antiferromagnetic state is longer than 100 nm, which is an order of magnitude longer than previously believed. These results provide a crucial…
For prospective spintronics devices based on the propagation of pure spin currents, antiferromagnets are an interesting class of materials that potentially entail a number of advantages as compared to ferromagnets. Here, we present a detailed theoretical study of magnonic spin current transport in ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics simulations. The relevant length scales of magnonic spin transport in antiferromagnets are determined. We demonstrate the transfer of angular momentum from a ferromagnet into an antiferromagnet due to the excitation of only …
Motivated by recent experiments [P. Vaidya {\em et al.}, Science {\bf 368}, 160 (2020)] on spin pumping from sub-THz radiation-driven uniaxial antiferromagnetic insulator (AFI) MnF$_2$ into heavy metal (HM) Pt hosting strong spin-orbit (SO) coupling, we compute and compare pumped spin currents in Cu/MnF$_2$/Cu and Pt/MnF$_2$/Cu heterostructures. Recent theories of spin pumping by AFI have relied on simplistic Hamiltonians (such as tight-binding) and the scattering approach to quantum transport yielding the so-called interfacial spin mixing conductance (SMC), but the concept of SMC ceases to be…
Control and detection of spin order in ferromagnets is the main principle allowing storing and reading of magnetic information in nowadays technology. The large class of antiferromagnets, on the other hand, is less utilized, despite its very appealing features for spintronics applications. For instance, the absence of net magnetization and stray fields eliminates crosstalk between neighbouring devices and the absence of a primary macroscopic magnetization makes spin manipulation in antiferromagnets inherently faster than in ferromagnets. However, control of spins in antiferromagnets requires e…
Spin pumping and spin-transfer torques are two reciprocal phenomena widely studied in ferromagnetic materials. However, pumping from antiferromagnets and its relation to current-induced torques have not been explored. By calculating how electrons scatter off a normal metal-antiferromagnetic interface, we derive pumped spin and staggered spin currents in terms of the staggered field, the magnetization, and their rates of change. For both compensated and uncompensated interfaces, spin pumping is of a similar magnitude as in ferromagnets with a direction controlled by the polarization of the driv…
SrIrO$_3$ with its large spin-orbit coupling and low charge conductivity has emerged as a potential candidate for efficient spin-orbit torque magnetization control in spintronic devices. We here report on the influence of an interfacial oxide layer on spin pumping experiments in Ni$_{80}$Fe$_{20}$ (NiFe)/SrIrO$_3$ bilayer heterostructures. To investigate this scenario we have carried out broadband ferromagnetic resonance (BBFMR) measurements, which indicate the presence of an interfacial antiferromagnetic oxide layer. We performed in-plane BBFMR experiments at cryogenic temperatures, which all…
Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was studied for a range of IrMn thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique `fingerprint' of the exchange bias and can be interpreted in terms of an…
Spin-transfer torque and spin Hall effects combined with their reciprocal phenomena, spin-pumping and inverse spin Hall (ISHE) effects, enable the reading and control of magnetic moments in spintronics. The direct observation of these effects remains elusive in antiferromagnetic-based devices. We report sub-terahertz spin-pumping at the interface of a uniaxial insulating antiferromagnet MnF2 and platinum. The measured ISHE voltage arising from spin-charge conversion in the platinum layer depends on the chirality of the dynamical modes of the antiferromagnet, which is selectively excited and mo…
The ac spin pumping of noncollinear antiferromagnets is theoretically investigated. Starting from an effective action description of the spin system, we derive the Onsager coefficients connecting the spin pumping and spin-transfer torque associated with the dynamics of the SO(3)-valued antiferromagnetic order parameter. Our theory is applied to a kagome antiferromagnet resonantly driven by a uniform external magnetic field. We demonstrate that the reactive (dissipative) spin-transfer torque parameter can be extracted from the pumped ac spin current in-phase (in quadrature) with the driving fie…
We consider the current-induced dynamics of insulating antiferromagnets in a spin Hall geometry. Sufficiently large in-plane currents perpendicular to the Néel order trigger spontaneous oscillations at frequencies between the acoustic and the optical eigenmodes. The direction of the driving current determines the chirality of the excitation. When the current exceeds a threshold, the combined effect of spin pumping and current-induced torques introduces a dynamic feedback that sustains steady-state oscillations with amplitudes controllable via the applied current. The ac voltage output is calcu…
In this work we focus on magnetic relaxation in Mn$_{80}$Ir$_{20}$(12 nm)/ Cu(6 nm)/ Py($d_\mathrm{F}$) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM) multilayers with different thickness of the ferromagnetic permalloy layer. An effective FM-AFM interaction mediated via the conduction electrons in the nonmagnetic Cu spacer -- the spin-pumping effect -- is detected as an increase in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of the resonant magnetic field. We further find experimentally that the spin-pumping-induced contribution to the linewidth is inversely proportional…
In a bilayer of ferromagnetic and non-magnetic metal, spin pumping can be generated by a thermal gradient. The spin current generation depends on the spin mixing conductance of the interface and the magnetic properties of the ferromagnetic layer. Due to its low intrinsic damping, rare earth iron garnet is often used for the ferromagnetic layer in the spin Seebeck experiment. However, it is actually a ferrimagnetic with antiferromagnetically coupled magnetic lattices and the contribution of rare earth magnetic lattice of rare earth iron garnet on thermal spin pumping is not well understand. Her…
In magnetic trilayer structures, a contribution to the Gilbert damping of ferromagnetic resonance arises from spin currents pumped from one layer to another. This contribution has been demonstrated for layers with weakly coupled, separated resonances, where magnetization dynamics are excited predominantly in one layer and the other layer acts as a spin sink. Here we show that trilayer structures in which magnetizations are excited simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as large. The antisymmetric (optical) mode of antiferromagnetically coupled Ni$_{79}$Fe$_…
Spintronics, since its inception, has mainly focused on ferromagnetic materials for manipulating the spin degree of freedom in addition to the charge degree of freedom, whereas much less attention has been paid to antiferromagnetic materials. Thanks to the advances of micro-nano-fabrication techniques and the electrical control of the Néel order parameter, antiferromagnetic spintronics is booming as a result of abundant room temperature materials, robustness against external fields and dipolar coupling, and rapid dynamics in the terahertz regime. For the purpose of applications of antiferromag…
We consider electron transport in ferromagnets or antiferromagnets sandwiched between metals. When spins in the magnetic materials precess, they emit currents into the surrounding conductors. Generally, adiabatic pumping in mesoscopic systems also enhances current fluctuations. We generalize the description of current fluctuations driven by spin dynamics in three ways using scattering theory. First, our theory describes a general junction with any given electron scattering properties. Second, we consider antiferromagnets as well as ferromagnets. Third, we treat multiterminal devices. Using sho…
We theoretically study the dynamic time evolution following laser pulse pumping in an antiferromagnetic insulator Cr$_{2}$O$_{3}$. From the photoexcited high-spin quartet states to the long-lived low-spin doublet states, the ultrafast demagnetization processes are investigated by solving the dissipative Schrödinger equation. We find that the demagnetization times are of the order of hundreds of femtosecond, in good agreement with recent experiments. The switching times could be strongly reduced by properly tuning the energy gaps between the multiplet energy levels of Cr$^{3+}$. Furthermore, th…
We present a $4'/m'$-respecting crisscross AFM model in 2D and 3D, both belonging to the $Z_2$ classification and exhibiting interesting magnetic high-order topological insulating (HOTI) phases. The topologically nontrivial phase in the 2D model is characterized by the fractional charge localized around the corners and the quantized charge quadrupole moment. Moreover, our 2D model also exhibits the quantized magnetic quadrupole moment, which is a unique feature compared with previous studies. The 3D system stacked from layers of the 2D model possesses the HOTI phase holding chiral 1D metallic …
Engineering photomagnetism in collinear van der Waals antiferromagnets
Radboud University, Institute for Molecules and Materials（拉德堡德大学分子与材料研究所）；HFML-FELIX；Institute of Physics, University of Amsterdam（阿姆斯特丹大学物理研究所）；Department of Physics, Technische Universität Dortmund（多特蒙德工业大学物理系）；Research Center Future Energy Materials and Systems（未来能源材料与系统研究中心）；King’s College London, Theory and Simulation of Condensed Matter（伦敦国王学院凝聚态理论模拟）
We investigate spin transport through metallic antiferromagnets using measurements based on spin pumping combined with inverse spin Hall effects in Ni80Fe20/FeMn/W trilayers. The relatively large magnitude and opposite sign of spin Hall effects in W compared to FeMn enable an unambiguous detection of spin currents transmitted through the entire FeMn layer thickness. Using this approach we can detect two distinctively different spin transport regimes, which we associate with electronic and magnonic spin currents respectively. The latter can extend to relatively large distances (up to 9 nm) and …
We propose a realization of the electric-field-induced antiferromagnetic resonance. We consider three-dimensional antiferromagnetic insulators with spin-orbit coupling characterized by the existence of a topological term called the $θ$ term. By solving the Landau-Lifshitz-Gilbert equation in the presence of the $θ$ term, we show that, in contrast to conventional methods using ac magnetic fields, the antiferromagnetic resonance state is realized by ac electric fields along with static magnetic fields. This mechanism can be understood as the inverse process of the dynamical chiral magnetic effec…
Antiferromagnets with vanishingly small (or zero) magnetization are interesting candidates for spintronics applications. In the present paper we propose two models for description of the current-induced phenomena in antiferromagnetic textures. We show that the magnetization that originates from rotation or oscillations of antiferromagnetic vector can, via $sd$-exchange coupling, polarize the current and give rise to adiabatic and nonadiabatic spin torques. Due to the Lorentz-type dynamics of antiferromagnetic moments (unlike the Galilenian-like dynamics in ferromagnets), the adiabatic spin tor…
