Tunable Magnetic Anisotropy Research Articles

Enhanced Ferromagnetism and Tunable Magnetic Anisotropy in a van der Waals Ferromagnet.

2D van der Waals (vdW) magnets have recently emerged as a promising material system for spintronic device innovations due to their intriguing phenomena in the reduced dimension and simple integration of magnetic heterostructures without the restriction of lattice matching. However, it is still challenging to realize Curie temperature far above room temperature and controllable magnetic anisotropy for spintronics application in 2D vdW magnetic materials. In this work, the pressure-tuned dome-like ferromagnetic-paramagnetic phase diagram in an iron-based 2D layered ferromagnet Fe3GaTe2 is reported. Continuously tunable magnetic anisotropy from out-of-plane to in-plane direction is achieved via the application of pressure. Such behavior is attributed to the competition between intralayer and interlayer exchange interactions and enhanced DOS near the Fermi level. The study presents the prominent properties of pressure-engineered 2D ferromagnetic materials, which can be used in the next-generation spintronic devices.

Harnessing ion beam erosion engineering for controlled self-assembly and tunable magnetic anisotropy in epitaxial films

The engineering of the surface morphology and the structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study presents an easy and handy approach to tailor the surface structure of epitaxial thin films utilizing low-energy ion beam. Here, we investigate the evolution of the surface structure and magnetic anisotropy (MA) in epitaxial Fe/MgO (001) model systems subjected to multiple cycles of ion beam erosion (IBE) after thin film growth. The growth of Fe film occurs in the form of three–dimensional islands and exhibits intrinsic biaxial MA. Following a few cycles of IBE, an induced uniaxial magnetic anisotropy leads to a split in the hysteresis loop, and the film displays almost uniaxial magnetic switching behavior. More distinctly, we present a clear and conclusive evidence of (2 × 2) reconstruction of the Fe surface due to the atomic rearrangement by IBE. Furthermore, 57Fe isotope sensitive nuclear resonance scattering measurement provides insight into the depth-resolved magnetic information due to the modified surface topography. We also demonstrate that thermal annealing can reversibly tune the surface reconstruction and induced UMA. The feasibility of the IBE technique by adequately selecting IBE parameters for surface structure modification has been highlighted apart from conventional tailoring of the morphology for the tuning of UMA and introduces a new dimension to our understanding of self-assembled surface morphology evolution by IBE.

Realization of logic operations via spin–orbit torque driven perpendicular magnetization switching in a heavy metal/ferrimagnet bilayer

Programmable and non-volatile spin-based logic devices have attracted significant interest for use in logic circuits. Realization of logic operations via spin–orbit torque (SOT) driven magnetization switching could be a crucial step in the direction of building logic-in-memory architectures. In this work, we demonstrate experimentally, the realization of four logic operations in a heavy metal/ferrimagnet bilayer structure via SOT switching. We also propose a general scheme for choosing input parameters to achieve programmable logic operations. The bulk and tunable perpendicular magnetic anisotropy and relatively lower saturation magnetization in ferrimagnets are found to make them more energy efficient in performing logic operations, as compared to conventional ferromagnets. Thus, ferrimagnets are promising candidates for use in logic-in-memory architectures, leading to the realization of user-friendly spin logic devices in the future.

Enhanced magnetic anisotropy of iridium dimers on antisite defects of two-dimensional transition-metal dichalcogenides.

The combination of transition-metal (TM) elements with two-dimensional (2D) transition-metal dichalcogenides (TMDs) provides an effective route to realizing a 2D controllable magnetic order, leading to significant applications in multifunctional nanospintronics. However, in most TM atoms@TMDs nanostructures, it is challenging for the magnetic anisotropy energy (MAE) to exceed 30 meV when affected by the crystal field. Hence, the stronger magnetic anisotropy of TMDs has yet to be developed. Here, utilizing first-principle calculations based on density functional theory (DFT), a feasible method to enhance the MAEs of TMDs via configurating iridium dimers (Ir2) on 2D traditional and Janus TMDs with antisite defects is reported. Calculations revealed that 28 of the 54 configurations considered possessed structure-dependent MAEs of >60 meV per Ir2 in the out-of-plane direction, suggesting the potential for applications at room temperature. We also showed the ability to tune the MAE further massively by applying a biaxial strain as well as the surface asymmetric polarization reversal of Janus-type substrates. This approach led to changes to >80 meV per Ir2. This work provides a novel strategy to achieve tunable large magnetic anisotropy in 2D TMDs. It also extends the functionality of antisite-defective TMDs, thereby providing theoretical support for the development of magnetic nanodevices.

Enhancing Interfacial Ferromagnetism and Magnetic Anisotropy of CaRuO3/SrTiO3 Superlattices via Substrate Orientation.

Artificial oxide heterostructures have provided promising platforms for the exploration of emergent quantum phases with extraordinary properties. One of the most interesting phenomena is the interfacial magnetism formed between two non-magnetic compounds. Here, a robust ferromagnetic phase emerged at the (111)-oriented heterointerface between paramagnetic CaRuO3 and diamagnetic SrTiO3 is reported. The Curie temperature is as high as ≈155K and the saturation magnetization is as large as ≈1.3µB per formula unit for the (111)-CaRuO3/SrTiO3 superlattices, which are obviously superior to those of the (001)-oriented counterparts and are comparable to the typical itinerant ferromagnet SrRuO3. A strong in-plane magnetic anisotropy with six-fold symmetry is further revealed by the anisotropic magnetoresistance measurements, presenting a large in-plane anisotropic field of 3.0-3.6T. More importantly, the magnetic easy axis of the (111)-oriented superlattices can be effectively tuned from 〈 1〉 to 〈 〉 directions by increasing the layer thickness of SrTiO3. The findings demonstrate a feasible approach to enhance the interface coupling effect by varying the stacking orientation of oxide heterostructures. The tunable magnetic anisotropy also shows potential applications in low-power-consumption or exchange spring devices.

Modulating above-room-temperature magnetism in Ga-implanted Fe5GeTe2 van der Waals magnets

The creation of van der Waals (vdW) ferromagnets with tunable Curie temperature (TC) and magnetic anisotropy is essential in developing vdW magnet-based devices. Here, we report an effective and reliable method for modulating the magnetic properties of vdW Fe5GeTe2 by site-specific Ga+ implantation. In this study, we report an easy axis in the ab-plane for bulk Fe5GeTe2 (TC = 310 K) and an axis out of the plane for thin Fe5GeTe2 flakes (TC = 290 K). Combining element-resolved photoemission electron microscopy and spatially resolved magneto-optic Kerr microscopy, we find that the implantation of a tiny amount of 10−3 Ga+·Å−3 in Fe5GeTe2 greatly enhances the TC from 290 to 360 K and switches the magnetic easy axis from the out-of-plane c axis to the ab-plane. The room-temperature x-ray magnetic circular dichroism signal is enhanced from 0% to 9% at an implantation level of 10−2 Ga+·Å−3. These results provide new opportunities for tailoring the magnetic properties of vdW materials beyond room temperature.

Manipulation of perpendicular magnetic anisotropy and spin–orbit torque switching behavior in ferrimagnetic D022-Mn3Ga based multilayers

Perpendicularly magnetized ferrimagnets have shown potential application in nonvolatile, high-density, and ultrafast spintronic devices. Achieving this requires tuning the material performance of ultrathin ferrimagnetic films. Here, we present an experimental demonstration of tunable perpendicular magnetic anisotropy (PMA) and spin–orbit torque (SOT) switching behavior in a ferrimagnetic Heusler alloy D022-Mn3Ga based multilayers by introducing lattice-matching underlayers. It is found that the highly (001) orientated crystalline structure is well maintained, whereas coercivity, anisotropy field, and PMA constant rely heavily on the specific underlayer. Owing to the strong out-of-plane exchange coupling, the PMA constant of Co2MnSi/D022-Mn3Ga is significantly enhanced by four times and reaches 12.1 Merg/cm3. Moreover, the SOT measurements suggest that Fe/D022-Mn3Ga and Co2MnSi/D022-Mn3Ga exhibit analog and abrupt switching dynamics, respectively. This contrasting SOT switching behavior is attributed to different magnetization switching mechanisms, verified by the direct imaging of the nanoscale magnetic domain. These results provide a deep insight into the manipulation of not only fundamental magnetic properties but also SOT switching of ferrimagnetic Heusler alloys.

Tunable magnetic anisotropy, half-metallicity and tunneling magnetoresistance effect of 2D CrI3 in CrI3/MnGeX3 (X = Se, Te) heterostructures under normal compressive strain

The induction of half-metallicity and tunable magnetic anisotropy of CrI3 monolayers remains challenging and unstable. In this study, we demonstrate that half-metallic CrI3 can be induced in a CrI3/MnGeX3(X = Se, Te) heterostructure. Normal compressive (NC) strain can effectively control the half-metallic band gap and spin-polarized electronic transport of CrI3 in CrI3/MnGeSe3. At 6% strain, the half-metallic band gap and equilibrium tunneling magneto-resistance (TMR) increases by 25% and 220%. The results of band structure, force theorem, charge density and work function calculations show that CrI3 in CrI3/MnGeSe3 loses electrons to form a hole-conducting half-metal with in-plane easy magnetization axis, while CrI3 gains electrons in CrI3/MnGeTe3 to form an electron-conducting half-metal with out-of-plane easy magnetization axis. Heterointerfacial half-metallicity in CrI3 is intrinsic without any external physical modification, and the NC strain of a two-dimensional structure can easily be realized experimentally, paving the way for further research of spintronic devices.

Tunable Magnetic and Optical Anisotropy in ZrO2‐Co Vertically Aligned Nanocomposites

AbstractMetamaterials have gained great research interest in recent years owing to their potential for property tunability, multifunctionality, and property coupling. As a new group of self‐assembled thin films, vertically aligned nanocomposite (VAN)‐based hybrid metamaterials have been demonstrated with significant anisotropic physical properties and a broad range of property tailorability, such as optical anisotropy, magnetic anisotropy, hyperbolic dispersion, and enhanced second harmonic generation properties. Herein, self‐assembled ZrO2‐Co nanocomposite films, with high epitaxial quality and ultra‐fine vertically aligned Co nanopillars (with an average diameter of ≈2 nm) embedded in a ZrO2 matrix, are fabricated using a pulsed laser deposition (PLD) method. The Co pillar density can be effectively tuned by varying the Co concentration in the target, which results in tunable optical properties and magnetic properties. Specifically, a high saturation magnetization of 100 emu cm−3, strong out‐of‐plane magnetic anisotropy and tailorable magnetization properties are achieved via tuning the Co nanopillar density. Coupled with hyperbolic dispersion of dielectric constant from 950 to 1500 nm in wavelength, plasmonic Co metal nanopillars, and the unique dielectric ZrO2 matrix, this new nanoscale hybrid metamaterial shows great potential for future integrated optical and magnetic device designs.

Second-harmonic signature of chiral spin structures in W/Pt/Co heterostructures with tunable magnetic anisotropy

Second-harmonic Hall voltage (SHV) measurement method has been widely used to characterize the strengths of spin–orbit torques (SOTs) in heavy metal/ferromagnet thin films saturated in the single-domain regime. Here, we show that the magnetic anisotropy of a W/Pt/Co trilayer can be robustly tuned from in-plane to out-of-plane by varying W, Pt, or Co thicknesses. Moreover, in samples with easy-cone anisotropy, SHV measurements exhibit anomalous ‘humps’ in the multidomain regime accessed by applying a nearly out-of-plane external magnetic field. These hump features can only be explained as a result of the formation of Néel-type domain walls, efficiently driven by nevertheless small SOTs in this double heavy metal heterostructure with canceling spin Hall angles.

Tuning the Magnetic Anisotropy of Co–N‐Doped Graphene

Large magnetic anisotropy energy and out‐of‐plane easy magnetization direction are beneficial for the application of 2D ferromagnetism. Although the robust room‐temperature ferromagnetism is reported in Co–N‐doped graphene [Nat. Commun. 2021, 12, 1854], its magnetic anisotropy and easy axis of magnetization are still unclear. Herein, the magnetic anisotropy of CoN4–graphene and CoN3–graphene is systematically studied. The CoN4–graphene has an in‐plane easy magnetization direction, while the easy magnetization direction of CoN3–graphene is out‐of‐plane. The magnetic anisotropy energy can be tuned by injecting charge or applying strain. Especially, for CoN3–graphene, both charge injection and tensile strain can tune the easy magnetization direction from out‐of‐plane to in‐plane. The tunable magnetic anisotropy may promote the application of Co–N‐doped graphene in spintronic devices.

Large Tunable Perpendicular Magnetic Anisotropy in Ultrathin Co -Based Ferromagnetic Films Induced by Antiferromagnetic δ−Mn

We report on the observation of large and tunable perpendicular magnetic anisotropy (PMA) in $\mathrm{Co}$-based ferromagnetic (FM) films induced by an antiferromagnetic (AFM) $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Mn}$ layer. The perpendicular anisotropic energy of the bilayers can be manipulated by varying the thickness of the $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Mn}$ layer and the maximum reaches 2.41 \ifmmode\times\else\texttimes\fi{} ${10}^{7}$ erg/cm${}^{3}$. The coercivity of bilayers is also effectively regulated over a broad range from 0.02 to 7.09 T. We demonstrate that this large PMA originates from strong interfacial exchange coupling and the AFM anisotropic energy. In addition, the antisymmetric longitudinal magnetoresistance occurs in the bilayers in the absence of asymmetric geometry or magnetic field. These results enrich our understanding of AFM-induced large PMA in an AFM/FM bilayer system and provide a promising bilayer structure for exploring high-density magnetic memory devices.

Two dimensional Janus RuXY (X, Y = Br, Cl, F, I, X ≠ Y) monolayers: ferromagnetic semiconductors with spontaneous valley polarization and tunable magnetic anisotropy.

Two-dimensional (2D) ferromagnetic (FM) materials with valley polarization are highly desirable for use in valleytronic devices. The 2D Janus materials have fascinating physical properties due to their asymmetrical structures. In this work, the electronic structure and magnetic properties of Janus RuXY (X, Y = Br, Cl, F, I, X ≠ Y) monolayers are systematically studied using first-principles calculations. RuBrCl, RuBrF, and RuClF monolayers are all FM semiconductors. The valley polarization is present in the band structure and this is determined by the spin orbit coupling (SOC). The valley splitting energy of the RuClF monolayer is as large as 204 meV, with a perpendicular magnetic anisotropy (PMA) energy of 1.918 mJ m-2 and a Curie temperature of 316 K. Therefore, spontaneous valley polarization at room temperature will be seen in the RuClF monolayer. The Curie temperature of the RuBrF monolayer is higher than that of the RuClF, but the magnetic anisotropy energy (MAE) is in-plane magnetic anisotropy (IMA). The valley splitting energy of the RuBrCl monolayer is higher and the PMA energy is lower than that of the RuClF monolayer. The Curie temperature was only 197 K. The valley polarization was modulated in the RuXY monolayers at different biaxial strains, during which the semiconductor properties are still maintained. The PMA of the RuClF and RuBrCl monolayers is enhanced by the biaxial compressive strains, which are mainly attributed to the variation of the (dyz, d2z) orbital matrix elements of the Ru atoms. The MAE of the RuBrF monolayer is tuned from IMA into PMA at a biaxial strain of -6%. These results show an example of a 2D Janus ferrovalley material.

Tunable electronic band structure and magnetic anisotropy in two-dimensional Dirac half-metal MnBr3 by external stimulus: strain, magnetization direction, and interlayer coupling.

Advancing technology and growing interdisciplinary fields create the need for new materials that simultaneously possess several significant physics qualities to meet human demands. Dirac half-metals with massless fermions hold great promise in spintronic devices and optoelectronic devices associated with nontrivial band topologies. In this work, we predict that a MnBr3 monolayer will be an intrinsic Dirac half-metal based on first-principles calculations. The lattice dynamics and thermodynamic stabilities were demonstrated by calculating the phonon spectra and performing molecular dynamics simulations. One property of a MnBr3 monolayer is that facile magnetization of its in-plane can be accomplished. A change in the magnetization direction significantly modifies the electronic band structure. When considering the spin-orbit coupling effect, the Dirac cone around the Fermi level in the spin-up channel opens a gap of 35 meV, which becomes a topological nontrivial insulator with a Chern number of -1. The Chern number sign and the chiral edge current can be tuned by changing the magnetization direction. The electronic band structure and magnetic anisotropy energy can be further modulated by applying biaxial and uniaxial strain, as well as introducing interlayer coupling in the bilayer. The unique performance of MnBr3 will broaden the utilization of two-dimensional magnetism in widespread application.

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.

Influence of surface roughness on magnetic properties of CoTbNi ternary alloy films

Rare earth-transition metal (RE-TM) amorphous alloys films with promising tunable perpendicular magnetic anisotropy are projected to be exploited for magnetic recording media and spintronic applications. Here variation of magnetic property of thin films of Co0·63Tb0·11Ni0.26, Co0·41Tb0·14Ni0.45 and Co0·32Tb0·08Ni0.60 ternary alloy fabricated on Si-substrate using dc magnetron sputtering at room temperature were studied. The x-ray diffraction pattern data confirms the amorphous nature of these alloy films. The average surface roughness (Sa and Ra) of the films is found to vary significantly with Ni content of the films. The room temperature field dependent magnetization measurement shows the room temperature ferromagnetism. The saturation magnetization and coercivity of the M-H curves are found to vary with Ni content as well as surface roughness of the films. However, the nature of variation of saturation magnetization and coercive field is in accordance with variation of surface roughness, indicating that film surface roughness play a vital role in tuning the magnetic properties of these thin films. Such tunable magnetic properties of these amorphous films make them good candidate for magnetic storage media applications.

Tunable magnetic anisotropy in SrMnO3/SrRuO3 bilayers studied by angle and temperature dependence of magneto-transport

Tunability of magnetic anisotropy in perovskite oxides, such as in SrRuO3, is commonly achieved by controlling the octahedral distortion through strain. Here, we demonstrate that differences in the oxygen vacancies at the heterointerface of SrMnO3/SrRuO3 can also strongly influence the magnetocrystalline anisotropy in SrRuO3 despite being fully strained by the underlying substrate. Modification of the spin–orbit coupling strength by altering the hybridization of Ru-4d and O-2p orbitals in SrRuO3 leads to a clear evolution of the magnetocrystalline anisotropy from multiaxial to strongly out-of-plane, as manifested in the magneto-transport studies. Our results provide an alternative design strategy for their incorporation in practical spintronic devices for memory and computing applications and operation by spin–transfer and spin–orbit torques.

Engineering Periodic Dinuclear Lanthanide‐Directed Networks Featuring Tunable Energy Level Alignment and Magnetic Anisotropy by Metal Exchange (Small 22/2022)

Lanthanide Multinuclear Networks In article number 2107073, Sofia O. Parreiras, David Écija, and co-workers demonstrate the tuning of the electronic and magnetic properties of dinuclear lanthanide metal–organic networks by metal exchange while preserving the same structural architecture. The exchange between Er and Dy metallic centers leads to a shift in the energy level alignment and allows the tailoring of both the intensity and orientation of magnetic anisotropy.

Magnetic Anisotropy Control with Curie Temperature above 400 K in a van der Waals Ferromagnet for Spintronic Device.

The technological appeal of van der Waals ferromagnetic materials is the ability to control magnetism under external fields with desired thickness toward novel spintronic applications. For practically useful devices, ferromagnetism above room temperature or tunable magnetic anisotropy is highly demanded but remains challenging. To date, only a few layered materials exhibit unambiguous ferromagnetic ordering at room temperature via gating techniques or interface engineering. Here, it is demonstrated that the magnetic anisotropy control and dramatic modulation of Curie temperature (Tc ) up to 400 K are realized in layered Fe5 GeTe2 via the high-pressure diamond-anvil-cell technique. Magnetic phases manifesting with in-plane anisotropic, out-of-plane anisotropic and nearly isotropic magnetic states can be tuned in a controllable way, depicted by the phase diagram with a maximum Tc up to 360 K. Remarkably, the Tc can be gradually enhanced to above 400 K owing to the Fermi surface evolution during a pressure loading-deloading process. Such an observation sheds light on the understanding and control of emergent magnetic states in practical spintronic applications.

Engineering Periodic Dinuclear Lanthanide-Directed Networks Featuring Tunable Energy Level Alignment and Magnetic Anisotropy by Metal Exchange.

The design of lanthanide multinuclear networks is an emerging field of research due to the potential of such materials for nanomagnetism, spintronics, and quantum information. Therefore, controlling their electronic and magnetic properties is of paramount importance to tailor the envisioned functionalities. In this work, a multidisciplinary study is presented combining scanning tunneling microscopy, scanning tunneling spectroscopy, X-ray absorption spectroscopy, X-ray linear dichroism, X-ray magnetic circular dichroism, density functional theory, and multiplet calculations, about the supramolecular assembly, electronic and magnetic properties of periodic dinuclear 2D networks based on lanthanide-pyridyl interactions on Au(111). Er- and Dy-directed assemblies feature identical structural architectures stabilized by metal-organic coordination. Notably, despite exhibiting the same +3 oxidation state, there is a shift of the energy level alignment of the unoccupied molecular orbitals between Er- and Dy-directed networks. In addition, there is a reorientation of the easy axis of magnetization and an increment of the magnetic anisotropy when the metallic center is changed from Er to Dy. Thus, the results show that it is feasible to tune the energy level alignment and magnetic anisotropy of a lanthanide-based metal-organic architecture by metal exchange, while preserving the network design.