Interfacial Magnetic Anisotropy Research Articles

Engineering Mn3Ga/GaAs interfaces: a first-principles study on energetic stability and magnetic anisotropy

Mn3Ga-based ferrimagnets have emerged as a promising platform for energy-efficient spintronics. However, the challenge of identifying an appropriate substrate with minimal lattice misfit for the growth of high-quality Mn3Ga films while achieving the desired interfacial magnetic properties persists. Here we investigate the interfacial energetic stability and magnetic anisotropy at the Mn3Ga/GaAs interface through first-principles electronic structure calculations. Four types of interface models based on different configurations, including MnMn/As, MnMn/Ga, MnGa/As, and MnGa/Ga, are systematically examined. Our findings reveal that the MnGa/Ga interface exhibits the largest perpendicular magnetic anisotropy (PMA) but is energetically the least favorable. Conversely, the MnMn/As interface is energetically the most favorable but demonstrates a lower interfacial PMA. Our calculations align well with the experimentally observed formation of the secondary phase Mn2As. This study deepens our understanding of the interfacial properties in Mn3Ga/GaAs and offers some insights for their optimization through strategic interfacial engineering.

Interfacial Magnetic Anisotropy Controlled Spin Pumping in Co60Fe20B20/Pt Stack

Controlled spin transport in magnetic stacks is required to realize pure spin current-driven logic and memory devices. The control over the generation and detection of the pure spin current is achieved by tuning the spin to charge conversion efficiency of the heavy metal interfacing with ferromagnets. Here, we demonstrate the direct tunability of spin angular momentum transfer and thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy. The ultra-low thickness of the CoFeB thin film by tilting the magnetization from in-plane to out-of plane direction due to interfacial anisotropy from higher thickness of CoFeB thin film. The ferromagnetic resonance measurements are performed to investigate the magnetic anisotropy and spin pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density, with varying ferromagnetic layer thickness, is found to increase from 1.10[Formula: see text]MA/m2 to 2.40[Formula: see text]MA/m2, with increasing in-plane anisotropy field. Such interfacial anisotropy-controlled generation of pure spin current can potentially lead to next-generation anisotropic spin current-controlled spintronic devices.

Perpendicular Magnetic Anisotropy of an Ultrathin Fe Layer Grown on NiO(001)

The magnetic anisotropy and magnetic interactions at the interface between $\mathrm{Fe}$ and $\mathrm{Ni}\mathrm{O}$(001) were investigated. Depending on the growth conditions of the $\mathrm{Ni}\mathrm{O}$(001) layers and the postannealing temperature, the preferential magnetization direction of the ultrathin $\mathrm{Fe}$ layer grown on a $\mathrm{Ni}\mathrm{O}$(001) layer changed from the in-plane direction to a direction perpendicular to the film plane. The lattice constant of the $\mathrm{Ni}\mathrm{O}$(001) layers parallel to the growth direction increased with ${\mathrm{O}}_{2}$ flow rate, while that parallel to the in-plane direction were locked onto the MgO(001) substrate regardless of the growth conditions of the NiO layers. Moreover, perpendicular magnetization was observed only when the NiO layer was grown with ${\mathrm{O}}_{2}$ flow rates higher than 2.0 sccm corresponding to oxygen-rich NiO. X-ray magnetic circular dichroism measurements revealed an enhancement in anisotropic orbital magnetic moments similar to the origin of perpendicular magnetic anisotropy at the $\mathrm{Fe}$/MgO(001) interface. The interfacial magnetic anisotropy energies were 0.93 and $1.02\phantom{\rule{0.2em}{0ex}}{\mathrm{mJ}/\mathrm{m}}^{2}$ at room temperature and at 100 K, respectively, indicating less temperature dependence. In contrast, the coercivity ${H}_{c}$ exhibited a significant temperature dependence. Although no signature of exchange bias or unidirectional loop shift was observed, ${H}_{c}$ was strongly dependent on the NiO layer thickness, indicating that the exchange interaction at the interface between the ferromagnetic and antiferromagnetic layers was not negligible, despite the NiO(001) being a spin-compensated surface.

Electrically excited magnetoelastic waves and magnetoacoustic resonance in ferromagnetic films with voltage-controlled magnetic anisotropy

Ferromagnet-dielectric heterostructures may possess interfacial magnetic anisotropy, which varies with the electric field created in the dielectric interlayer. Such a voltage-controlled magnetic anisotropy (VCMA) represents an efficient tool for the excitation of spin waves without the use of microwave magnetic fields. In ferromagnets with a significant magnetoelastic coupling between spins and strains, however, the magnetization precession in the spin wave induces elastic vibrations. Here we report micromagnetoelastic simulations of the coupled spin and acoustic dynamics generated in the thick Fe film brought into contact with an MgO nanolayer subjected to a microwave voltage. It is found that the electrically induced periodic modulation of VCMA gives rise to the excitation of both spin and elastic waves in the magnetostrictive Fe film. Remarkably, the magnetoelastic coupling makes it possible to generate propagating spin waves having frequencies well below the ferromagnetic resonance frequency. Furthermore, when the voltage frequency approaches a value ${\ensuremath{\nu}}^{*}$ at which the dispersion relations of pure spin and transverse elastic waves cross, the excitation of traveling magnetoelastic waves with a specific hybrid dispersion occurs in the Fe film. To explain the variety of observed phenomena, we propose a generalized dispersion relation for magnetoelastic waves, which accounts for a possible difference between the wave numbers of their magnetic and elastic components. The analysis of the simulation data also reveals that frequency dependencies of the amplitudes of magnetic oscillations and elastic vibrations display significant anomalies around the crossing-point frequency ${\ensuremath{\nu}}^{*}$, which originate from the electrically induced magnetoacoustic resonance.

Giant and strain-tunable interfacial magnetic anisotropy in MgO-based magnetic heterostructures with heavy atoms insertion

MgO-based magnetic heterostructures with interfacial magnetic anisotropy has attracted increasing attention due to its application in building high-density magnetic random access memories. A large and tunable interfacial magnetic anisotropy constant (Ki) is required for high thermal stability and flexible data writability. In this study, the Ki of Fe/MgO, Fe/Pt/MgO, and Fe/Ir/MgO heterostructures with strains from −4.5% to 4.5% were calculated by ab initio electronic structure calculations. It has been found that the Fe/Pt/MgO and Fe/Ir/MgO where the Pt and Ir monolayers are inserted in the interface possess Ki of 2.415 mJ m−2 and −4.468 mJ m−2, which are much larger by several times than that (0.840 mJ m−2) of the Fe/MgO. In particular, the out-of-plane Ki from the interfacial Pt atoms in Fe/Pt/MgO is as high as 5.978 mJ m−2. The magnetic anisotropy of these structures can be significantly manipulated by strain. Combining second-order perturbation theory, the origin of these behaviors has been analyzed by layer-resolved, orbital-resolved, and k-resolved Ki. The spin-flip terms of d z 2/d yz orbitals in the interfacial layer are mainly responsible for the out-of-plane Ki and its variation with strain. This work provides a useful guide for the design of high and tunable magnetic anisotropy in the MgO-based magnetic heterostructures.

Interface change of Pr-Fe-B thin films with different ferromagnetic compositions

The thin film structure of the Si3N4/Pr-Fe-B/Si3N4/glass substrate was fabricated by the sputtering process followed by an in-situ annealing process at 650 °C. The changes at the interface of magnetic layer/underlayer were investigated with simultaneous addition of Fe content in the range of 68.9 to 76.61 at.% during the sputtering process. With ferromagnetic properties and more reactive and movable capacity of Fe, the addition of Fe created significant changes in the crystal structure, surface morphology, microstructure, and magnetic properties in Pr-Fe-B thin films. X-ray diffraction results confirmed the presence of two Pr2Fe14B and Pr2Fe23B3 magnetic phases in the thin films. The surface morphology of the thin films observed through SEM pictures and AFM images showed the blossom phenomenon with various grain sizes and surface roughness, respectively. The microstructure of the thin films through HR-TEM pictures revealed the discernable change at the interface of the Pr-Fe-B layer/Si3N4 underlayer. The new Fe3Si underlayer formed different thicknesses at the interface corresponding to various Fe contents. The stacking of (100) and (010) planes of Pr2Fe14B phase with different d-spacings was observed at higher magnification of HR-TEM. Results of magnetic measurement showed that the thin film at 73.32 at.% Fe content had the better growth potential of perpendicular magnetic anisotropy (PMA) and obtained a higher coercivity of approximately 4.5 kOe. MFM images through magnetic domain observation showed that the thin films had the same magnetic domain pattern but varied in magnetic domain size. Analysis of saturation magnetization and effective uniaxial anisotropy of the thin films showed the contribution of the interface magnetic anisotropy (to the PMA with the value of Ki = 122.25 × 106 erg/m2.

Electrical Manipulation of Oxygen Ion Migrations for the Voltage‐Controlled Adjustment of Magnetic Anisotropy and Optimized Skyrmion Generations

AbstractWith the prospect of energy‐efficient spintronics by voltage‐controlled magnetic anisotropy (VCMA), various mechanisms are investigated involving electron orbital state modulations for enhanced spin–orbit interactions, couplings with piezoelectric strain, and electrochemical effect at the interface within diverse magnetoelectric coupled material systems. In the present work, chemistry and spatial distributions of atoms are fine‐tuned at the interface between ferromagnetic Co and partially oxidized Gd layers via voltage‐controlled ion migrations, achieving highly sensitive and stable VCMA operations. With combined actions of chemical diffusion and electrical driving of oxygen through amorphous Gd layer, asymmetric electrical adjustments of magnetic anisotropy could be established. Accompanied changes in the domain morphologies in the magnetic thin film layers could also be confirmed at room temperature. As the fine‐adjustments of domain morphology are essential for the skyrmions generation, voltage‐controlled interfacial chemistry and magnetic anisotropy provide an effective route to stable skyrmion generations and manipulations in the low‐power spintronics technology.

Giant Orbital Anisotropy with Strong Spin–Orbit Coupling Established at the Pseudomorphic Interface of the Co/Pd Superlattice

Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin–orbit‐related phenomena. However, modulating the interface's electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low‐energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3O4/Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3O4 into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin–orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature‐dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin–orbit coupling at the interface is key to exploring spintronic devices with new functionalities.

Unveiling Temperature-Dependence Mechanisms of Perpendicular Magnetic Anisotropy at Fe / MgO Interfaces

The perpendicular magnetic anisotropy (PMA) at magnetic transition metal/oxide interfaces is a key element in building out-of-plane magnetized magnetic tunnel junctions for spin-transfer-torque magnetic random access memory (STT-MRAM). Size downscaling renders magnetic properties more sensitive to thermal effects. Thus, understanding the temperature dependence of the magnetic anisotropy is crucial. In this work, we theoretically address the correlation between temperature dependence of PMA and magnetization in typical Fe/MgO-based structures. In particular, the possible mechanisms behind the experiments reporting deviations from the Callen and Callen scaling power law are analyzed. At ideal interfaces, first-principles calculations reveal (i) small high-order anisotropy constants compared to first order and (ii) enhanced exchange constants. Considering these two intrinsic effects in the atomistic simulations, the temperature-dependence of the total and layer-resolved anisotropy are found to follow the Callen and Callen scaling power law, thus ruling out an intrinsic microscopic mechanism underlying deviations from this law. Besides, two possible extrinsic macroscopic mechanisms are unveiled namely the influence of the dead layer, often present in the storage layer of STT-MRAM cells, and the spatial inhomogeneities of the interfacial magnetic anisotropy. About the first mechanism, we show that the presence of a dead layer tends to reduce the scaling exponents. In the second mechanism, increasing the percentage of inhomogeneity in the interfacial PMA is revealed to decrease the scaling exponent. These results allow us to explain the difference in scaling exponents relating anisotropy and magnetization thermal variations reported in earlier experiments. This is crucial for the understanding of the thermal stability of the storage layer magnetization in STT-MRAM applications.

Electric field induced parametric excitation of exchange magnons in a CoFeB/MgO junction

Inspired by the success of field-effect transistors in electronics, electric field controlled magnetization dynamics has emerged as an important integrant in low-power spintronic devices. Here, we demonstrate electric field induced parametric excitation for CoFeB/MgO junctions by using interfacial in-plane magnetic anisotropy (IMA). When the IMA and the external magnetic field are parallel to each other, magnons are efficiently excited by electric field induced parametric resonance. The corresponding wavelengths are estimated to be tuned down to exchange interaction length scales by changing the input power and frequency of the applied voltage. A generalized phenomenological model is developed to explain the underlying role of the electric field torque. Electric field control of IMA is shown to be the origin for excitation of both uniform and parametric resonance modes in the in-plane magnetized sample, a crucial element for purely electric field induced magnetization dynamics. Electric field excitation of exchange magnons, with no Joule heating, offers a good opportunity for developing nanoscale magnonic devices and exploring various nonlinear dynamics in nanomagnetic systems.

Elucidate interfacial disorder effects on the perpendicular magnetic anisotropy at Fe/MgO heterostructure from first-principles calculations

The interfacial perpendicular magnetic anisotropy (PMA) plays a key role in spintronic applications such as memory recording and computational devices. Despite robust PMA being reported at the Fe/MgO interface, there are still inconsistencies in the disorder effects on the interfacial magnetic anisotropy. Here we reported a comprehensive study of the influence of the interfacial disorder, including the underoxidization, overoxidization, and oxygen migration, on the PMA of the Fe/MgO interface using first-principles calculations. Compared to the pristine Fe/MgO interface, the underoxidation at the Fe/MgO interface keeps the interfacial PMA but reduces the interfacial anisotropy constant (K i ). The overoxidization and oxygen migration at the interface both reduce the K i and even switch the easy magnetization axis from the out-of-plane to in-plane direction at high oxygen percentage. In all the cases, the K i was found strongly correlated to the difference of the orbital magnetic moment along the in-plane and out-of-plane direction. Calculated layer-resolved and orbital-resolved K i revealed that the orbital coupling between the d xy and states of the interfacial Fe layer plays a key role in determining the interfacial magnetic anisotropy. This work provides deep insights into the oxidation effects on the interfacial magnetic anisotropy of Fe/MgO system and a possible avenue to tune the K i via interfacial engineering.

Extraction of the chemical contribution to the interfacial magnetic anisotropy in Ni/Cu3Au(001)

The manipulation of magnetic anisotropy via interface is crucial for spintronics, but its mechanism is still controversial due to the parasitic problem of strain and the chemistry environment. We have independently controlled the interfacial chemistry of the epitaxially grown Ni film on ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ by inserting the thickness wedged Cu layer. The Ni layer is confirmed to be fully strained until 8 ML by the analysis of LEED I-V spectra, which guarantees that the strain contributions to the magnetic anisotropies are identical. Our results clearly show that the chemistry contribution of Au atoms at $\mathrm{Ni}/{\mathrm{Cu}}_{3}\mathrm{Au}$ interface plays a major role for its perpendicular magnetic anisotropy. We provide a method to quantitatively separate and extract the chemistry and strain contributions to the interfacial magnetic anisotropy, which is helpful for clarifying its mechanism and developing high performance spintronic materials and devices.

Control of Interfacial Magnetic Anisotropy of CoFeB/MgO by X-ray Magnetic Circular Dichroism

Control of Interfacial Magnetic Anisotropy of CoFeB/MgO by X-ray Magnetic Circular Dichroism

Current-induced magnetization switching in perpendicularly magnetized V/CoFeB/MgO multilayers

The perpendicular magnetic anisotropy properties of CoFeB/MgO films on $3d$ light-metal vanadium have been experimentally investigated. The interfacial magnetic anisotropy is $1.4\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}^{2}$ for the V/CoFeB/MgO multilayers annealed at 240 \ifmmode^\circ\else\textdegree\fi{}C. A sign change of the effective torque fields with the increase of V thickness has been observed, which is confirmed by current-induced magnetization switching measurements, suggesting a competition of multiple effects on current-induced torques in the weakly spin-orbit coupled V/CoFeB/MgO multilayers. These findings have implications for the fundamental understanding of current-induced torque and further device applications using $3d$ light transition-metal based heterostructures.

Evidence of a C60 /Co interface reconstruction and its influence on magnetic properties

By using grazing incidence x-ray diffraction and scanning tunneling microscopy experiments, we determine the interface structure of a ${\mathrm{C}}_{60}$ layer deposited on a Co(0001) surface. The room temperature deposition gives rise to a ($4\ifmmode\times\else\texttimes\fi{}4$) molecular structure with a 10% vertical relaxation of the underneath Co atoms. When annealed around 550 K, the interface undergoes a structural change with most of the buckyballs sitting in a seven Co vacancies nanohole. Ab initio calculations show that this interface reconstruction is stabilized by a strong C-Co hybridization and has a significant impact both on the interfacial magnetic anisotropy that is decreased and on the molecular spin polarization that it increased.

Disentangling intrinsic and extrinsic Gilbert damping

Magnetic damping is of great interest due to its importance in magnetization switching and dynamics. Here, we report the quantitative disentanglement of intrinsic and extrinsic Gilbert damping in epitaxial Fe thin films. Both intrinsic damping and two-magnon scattering (TMS) make significant contributions to the total Gilbert damping, leading to an enhanced total damping at low temperature. Our result suggests the correlation between interfacial magnetic anisotropy and TMS.

The large perpendicular magnetic anisotropy induced at the Co2FeAl/MgAl2O4 interface and tuned with the strain, voltage and charge doping by first principles study

The heterostructures with high perpendicular magnetic anisotropy (PMA) have advantages for the application of the nonvolatile memories with long data retention time and small size. The interface structure and magnetic anisotropy energy (MAE) of Co2FeAl/MgAl2O4 heterostructures were studied by first principles calculations. The stable interface atomic arrangement is the Co or FeAl layer located above the equatorial oxygen coordinate in the distorted oxygen octahedrons. The Co–O interface can induce large effective PMA up to 4.54 mJ m−2, but this structure is a metastable structure. Meanwhile, the effective MAE decreases linearly as the thickness of the ferromagnetic layer increase. The effective MAE for the FeAl–O interface is only 1.3 mJ m−2, while the maximum thickness of Co2FeAl layer that maintains the PMA effect is about 1.717 nm. These values are very close to the experimental results. Through d-orbital-resolved MAE, we confirm that the interface PMA is mainly originated from the hybridization between and orbitals of interface 3d atoms. In addition, the compressive strain, negative electric field and hole doping can significantly enhance the effective PMA of FeAl–O interface. At the same time, Co–O interface will become the most stable structure by tuning the Mg/Al ratio in the spinel layers. The large effective PMA makes the Co2FeAl/MgAl2O4 junction a perfect candidate for the next-generation of non-volatile spintronic devices.

Direct observation of topological charge impacting skyrmion bubble stability in Pt/Ni/Co asymmetric superlattices

We characterize the magnetic properties and domain structure of Pt/Ni/Co asymmetric superlattices in comparison to the more established Pt/Co/Ni structure. This reversal in stacking sequence leads to a marked drop in interfacial magnetic anisotropy and the magnitude of the interfacial Dzyaloshinskii–Moriya interaction as inferred from the domain wall (DW) structure, which we speculate could be related to a degradation of the Pt/Co interface when Pt is deposited on top of the Co layer. Lorentz transmission electron microscopy exclusively reveals Néel-type DWs and, with a perpendicular field, Néel skyrmions in the Pt/Co/Ni films. Conversely, the Pt/Ni/Co samples show only achiral Bloch DWs, which leads to the formation of achiral Bloch and type II bubbles at an increased perpendicular field. Combined with the reduced anisotropy leading to greater bubble densities, the latter case makes for an excellent test bed to examine the benefits of topological charge on stability. Simultaneous observation of Bloch and type II bubbles shows a roughly 50 mT larger annihilation field for the former. An in-plane component to the magnetic field is shown to both impact the structure of the formed bubbles and separately suppress the topological benefit.

Origin of magnetic anisotropy, role of induced magnetic moment, and all-optical magnetization switching for Co100−xGdx/Pt multilayers

The combination of Co, Gd, and Pt materials is a representative with perpendicular magnetic anisotropy (PMA) for the all-optical switching (AOS), which provides a promising route for ultrafast magnetization manipulation. This paper shows that the PMA of Co100−xGdx/Pt multilayers mainly originates not from the bulk property of ferrimagnetic Co100−xGdx but from the interface magnetic anisotropy between the Co100−xGdx and Pt layers. In addition, the contribution of magnetic moment induced in Pt becomes remarkable, which modulates the compensation temperature for the samples with thin Co100−xGdx layers. The Co100−xGdx/Pt multilayers exhibited the all-optical helicity-independent switching in a wide range of Gd concentrations, and the maximum AOS probability was achieved near the compensation composition. We discuss the correlation between the magnetic properties and the AOS probability for the Co100−xGdx/Pt multilayers. The AOS showed clear thickness dependence, which was attributable to the remarkable contribution of induced moment. Our findings are beneficial not only for understanding the mechanism of AOS but also for designing spintronic devices using ferrimagnets.

Magnetic anisotropy manipulation and interfacial coupling in Sm3Fe5O12 films and CoFe/Sm3Fe5O12 heterostructures* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0303603 and 2016YFA0401803), the National Natural Science Foundation of China (Grant Nos. U2032218, 11574316, 11874120, 61805256, and 11904367), the Plan for Major Provincial Science & Technology Project (Grant No. 202003a05020018), and the Key Research

The magnetic anisotropy manipulation in the Sm3Fe5O12 (SmIG) films and its effect on the interfacial spin coupling in the CoFe/SmIG heterostructures were studied carefully. By switching the orientation of the Gd3Ga5O12 substrates from (111) to (001), the magnetic anisotropy of obtained SmIG films shifts from in-plane to out-of-plane. Similar results can also be obtained in the films on Gd3Sc2Ga3O12 substrates, which identifies the universality of such orientation-induced magnetic anisotropy switching. Additionally, the interfacial spin coupling and magnetic anisotropy switching effect on the spin wave in CoFe/SmIG magnetic heterojunctions have also been explored by utilizing the time-resolved magneto–optical Kerr effect technique. It is intriguing to find that both the frequency and effective damping factor of spin precession in CoFe/SmIG heterojunctions can be manipulated by the magnetic anisotropy switching of SmIG films. These findings not only provide a route for the perpendicular magnetic anisotropy acquisition but also give a further path for spin manipulation in magnetic films and heterojunctions.