Strong In-plane Magnetic Anisotropy Research Articles

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.

Perpendicular magnetic anisotropy induced by antiferromagnetic Mn-Pd alloy films: Dual effects of exchange and spin-orbit coupling

Ferromagnetic (FM) films with perpendicular magnetic anisotropy (PMA) are crucial building blocks of state-of-the-art perpendicular magnetic devices. This study investigated the effects of triggering PMA in FM thin films by applying ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-based antiferromagnetic (AFM) thin films with strong AFM exchange coupling from Mn and high spin-orbit coupling from Pd atoms. Our results reveal that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films can trigger PMA in Co/Ni films with weak in-plane magnetic anisotropy at room temperature through either ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-facilitated interfacial perpendicular crystalline anisotropy (spin-orbit coupling, $x \ensuremath{\ge}10%$) or incorporation of them with antiferromagnet-induced exchange coupling ($x \ensuremath{\le}10%$). In Co/Fe films with strong in-plane magnetic anisotropy, Mn-rich ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films ($x \ensuremath{\le}10%$) can induce stable PMA at low temperatures through concurrently enhanced spin-orbit coupling and antiferromagnet-induced exchange coupling across the AFM--FM interface. Our research clarifies the dual effects of exchange and spin-orbit coupling in ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films, which trigger the PMA of adjacent FM films. This indicates that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films are promising candidates for achieving controllable PMA.

Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic Co/Fe films with strong in-plane magnetic anisotropy

Ferromagnetic (FM) films with higher magnetic moment density typically exhibit sizable in-plane magnetic anisotropy as a result of strong dipolar interactions, which hinder their application in state-of-the-art perpendicularly based magnetic devices. This study reports the effects of triggering the perpendicular magnetic anisotropy (PMA) of a Co/Fe film with strong in-plane magnetic anisotropy through nearby antiferromagnetic (AFM) fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ and face-centered tetragonal (e-fct) Mn films. Our results demonstrate that fcc ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ films with a three-dimensional quadratic AFM spin structure can trigger robust PMA in a Co/Fe film through collinearlike AFM-FM exchange coupling at room temperature. Furthermore, by incorporating a monolayered ${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ film into the Mn-Co interface or by reducing the temperature, PMA can also be triggered in a Co/Fe film by using e-fct Mn films with an in-plane-oriented AFM spin structure at room or low temperature through noncollinear exchange coupling across the AFM-FM interface. Our results clarify the exchange-coupling mechanisms, characteristic behaviors, and critical conditions for increasing control over antiferromagnet-induced PMA in FM films with high magnetic moment density but strong in-plane magnetic anisotropy, which is helpful for the development of next-generation perpendicularly based spintronic devices.

Interfacial spin-orbit torques and magnetic anisotropy in WSe2/permalloy bilayers

Transition metal dichalcogenides (TMDs) are promising materials for efficient generation of current-induced spin-orbit torques (SOTs) on an adjacent ferromagnetic layer. Numerous effects, both interfacial and bulk, have been put forward to explain the different torques previously observed. Thus far, however, there is no clear consensus on the microscopic origin underlying the SOTs observed in these TMD/ferromagnet bilayers. To shine light on the microscopic mechanisms at play, here we perform thickness dependent SOT measurements on the semiconducting WSe2/permalloy bilayer with various WSe2 layer thickness, down to the monolayer limit. We observe a large out-of-plane field-like torque with spin-torque conductivities up to . For some devices, we also observe a smaller in-plane antidamping-like torque, with spin-torque conductivities up to , comparable to other TMD-based systems. Both torques show no clear dependence on the WSe2 thickness, as expected for a Rashba system. Unexpectedly, we observe a strong in-plane magnetic anisotropy—up to about erg cm−3—induced in permalloy by the underlying hexagonal WSe2 crystal. Using scanning transmission electron microscopy, we confirm that the easy axis of the magnetic anisotropy is aligned to the armchair direction of the WSe2. Our results indicate a strong interplay between the ferromagnet and TMD, and unveil the nature of the SOTs in TMD-based devices. These findings open new avenues for possible methods for optimizing the torques and the interaction with interfaced magnets, important for future non-volatile magnetic devices for data processing and storage.

Magnetic properties of Pr bulk and clusters determined using density functional theory calculations

Lanthanide-based nanostructures have the potential to meet the current miniaturization demands of advanced devices such as magnetic memories with ultrahigh-storage densities. However, many questions about their fundamental properties remain unaddressed even for bulk and small nanostructures. From the application and scientific point of view, it is crucial to determine their structural stability, magnetic coupling, and magnetic anisotropy, as well as to identify the best structure that can simultaneously consider these properties. With the help of experimental measurements on Pr bulk and clusters, we quantitatively calculated the spin and orbital magnetic moments by using the density functional theory (DFT) method, where spin-orbit coupling (SOC) and non-collinearity are included self-consistently. We found that Pr bulk is in a singlet state with the atomic magnetic moments anti-ferromagnetically coupled along the in-plane direction, and it shows strong in-plane magnetic anisotropy. Obeying Hunds rule of negative values, the orbital magnetic moment remarkably contributes to total moments in the bulk and cluster phases. However, they cannot determine the experimental oscillation of cluster magnetism. The oscillation behavior, as a function of cluster size, as well as the enhanced magnetic moment with increasing temperature, can be interpreted as the anti-ferromagnetic coupling between atomic magnetic moments. Giant magnetic anisotropy energy of several hundreds of meV has been derived in both Pr bulk and clusters, which is an order of magnitude larger than the transition metal counterparts.

Tetragonal distortion induced perpendicular magnetic anisotropy in (Fe0.5Ni0.5)xRh1−x alloy thin films

We investigated the structural and magnetic properties of (Fe0.5Ni0.5)xRh1−x alloy thin films grown on MgO (100) substrate. The crystal lattice parameters of the alloy are tailored via the tetragonal distortion from the substrate by varying the composition. The change in the lattice parameters and compositions allowed us to control the magnetic properties as well. For thin films with a higher concentration of ferromagnetic content exhibit strong in-plane magnetic anisotropy. Perpendicular magnetic anisotropy (PMA) was observed around 40% of FeNi. We show that the main contribution to the PMA around 40% FeNi is originated from the tetragonal distortion in the crystal, via first-principles calculations.

Atomic-Scale Mechanism of Grain Boundary Effects on the Magnetic and Transport Properties of Fe3O4 Bicrystal Films.

In strongly correlated materials, change of the local lattice configuration is expected to tune or even generate new properties otherwise in the ideal bulk materials. For highly spin-polarized materials, the spin-dependent transport is sensitive to the local magnetic structure. Here, the artificial grain boundaries (GBs) with different tilt angles are produced in Fe3O4 films using SrTiO3 bicrystal substrates. The saturation magnetization of Fe3O4 bicrystal films is enhanced. The detailed atomic structural results combining with density functional theory calculations reveal that the elongated FeA-O bond length at GBs resulting in the reduction of charge transfer reduces the FeA magnetic moments, which enhances the total magnetic moments of Fe3O4. The in-plane rotation of the Fe3O4 lattice on bicrystal substrates alters the magnetization processes. Especially, the Fe3O4 bicrystal film with a tilt angle of 22.6° shows strong in-plane magnetic anisotropy due to the zigzag GBs. The altered magnetic anisotropy of Fe3O4 bicrystal films enhances the anisotropic magnetoresistance. The findings reveal the mechanism of GBs on the magnetic and transport properties and manifest that the strategy of utilizing GBs can tune the physical properties in highly spin-polarized materials.

Néel-type antiferromagnetic order and magnetic field–temperature phase diagram in the spin- 12 rare-earth honeycomb compound YbCl3

Most of the searches for Kitaev materials deal with $4d/5d$ magnets with spin-orbit-coupled $J=1/2$ local moments such as iridates and $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$. Here we propose the monoclinic ${\mathrm{YbCl}}_{3}$ with a ${\mathrm{Yb}}^{3+}$ honeycomb lattice for the exploration of Kitaev physics. We perform thermodynamic, $ac$ susceptibility, angle-dependent magnetic torque, and neutron diffraction measurements on ${\mathrm{YbCl}}_{3}$ single crystal. We find that the ${\mathrm{Yb}}^{3+}$ ion exhibits a Kramers doublet ground state that gives rise to an effective spin ${J}_{\text{eff}}=1/2$ local moment. The compound exhibits short-range magnetic order below 1.20 K, followed by a long-range N\'eel-type antiferromagnetic order at 0.60 K, below which the ordered ${\mathrm{Yb}}^{3+}$ spins lie in the $ac$ plane with an angle of 16(11)${}^{\ensuremath{\circ}}$ away from the $a$ axis. These orders can be suppressed by in-plane and out-of-plane magnetic fields at around 6 and 10 T, respectively. Moreover, the N\'eel temperature varies nonmonotonically under the out-of-plane magnetic fields, suggesting a reduced spin dimensionality. Together with the strong in-plane magnetic anisotropy and the reduced order moment 0.8(1) ${\ensuremath{\mu}}_{B}$ at 0.25 K, all indicate that ${\mathrm{YbCl}}_{3}$ could be a two-dimensional spin system to proximate the Kitaev physics.

High energy product FexPt100-x thin films (x = 60–66) prepared by rapid thermal annealing

Magnetic properties of sputtered FexPt100-x (x = 60–66) thin films via rapid thermal annealing (RTA) are studied. The structural results show that FexPt100-x films through RTA at Ta above 400 °C exhibit (00L) texture. (00L) texture is considered to result from L10 phase and L12 phase. All studied FexPt100-x films through RTA at Ta = 300–600 °C exhibit strong in-plane magnetic anisotropy with well-squared M-H curve and good permanent magnetic properties. Fine microstructure with small size of grain here gives arise to high Mr and good squareness of demagnetization curve. Magnetic force microscopy shows a fine interaction domain. Strong exchange coupling effect between grains due to fine microstructure results in high remanence and therefore (BH)max. As a result, high coercivity of 5.7 kOe and a maximum (BH)max of 26.0 MGOe are achieved. The results of this study reveal that Fe-rich FexPt100-x thin films (x = 60–66) through RTA is a cost-effective and simple method to obtain high energy product, which could be useful for related applications.

Magnetic anisotropy and magnetostrictive properties of sputtered Tb–Dy–Fe–Co thin films

Tb–Dy–Fe–Co thin films grown on Si $$\left\langle {100} \right\rangle$$ substrates at different substrate temperatures viz., room temperature, 300, 400 and 500 °C were investigated for structural, microstructural, magnetic and magnetostrictive properties. Grazing incidence X-ray diffraction studies showed presence of amorphous structure for the as-deposited film. Structural studies further indicated formation of (Tb,Dy)2(Fe,Co)17 and Fe–Co phases for the films grown at higher substrate temperatures. Magnetization measurements displayed presence of strong in-plane magnetic anisotropy for all the films. In addition to this, formation of out-of-plane magnetic anisotropy co-existing with in-plane magnetic anisotropy was noticed for the films grown at higher substrate temperatures. Accordingly, magnetic force microscopy studies indicated a strong out-of-plane magnetic contrast for the films grown at higher substrate temperatures. The magnetostriction estimated from tip deflection measurement was found to be negligibly small for the film grown at intermediate temperature viz., 300 °C. However, with subsequent increase in substrate temperatures the magnetostriction was found to increase. The presence of strong out-of-plane magnetic anisotropy co-existing with in-plane components was found to be detrimental for the development of magnetostriction.

Magnetostriction and Magnetic Microscopy Studies in Fe-Co-Si-B Thin Films

This paper reports the effect of substrate temperature on the magnetostrictive behavior of sputtered Fe-Co-Si-B thin films. Magnetostriction measurements carried out by measuring the tip deflection in thin film cantilevers were found to increase with increase in substrate temperatures. To understand the variation of magnetostriction with substrate temperature, detailed structural, microstructural, magnetization and domain imaging studies were carried out. Magnetization studies indicated presence of strong in-plane magnetic anisotropy for all the films. The change in the in-plane coercivity with increase in substrate temperature was correlated with grain size and surface roughness effects. Angular dependent magnetic hysteresis and domain imaging studies carried out using longitudinal Magneto-optic Kerr microscopy displayed presence of strong in-plane uniaxial anisotropy for the as deposited film. Upon increase in substrate temperature, in-plane anisotropic nature was found to gradually change towards isotropic nature owing to the enhancement in crystallization and relaxation of stresses. The magnetization reversal along the in-plane easy axis and hard axis of magnetization was found to be dominated by domain wall motion and through a combination of coherent rotation, domain wall motion & rotation respectively. The increase in the magnetostriction with substrate temperature was correlated with the strong interplay between the crystallization, grain size and magnetic anisotropy.

Epitaxial integration of CoFe2O4 thin films on Si (001) surfaces using TiN buffer layers

Epitaxial cobalt ferrite thin films with strong in-plane magnetic anisotropy have been grown on Si (001) substrates using a TiN buffer layer. The epitaxial films have been grown by ion beam sputtering using either metallic, CoFe2, or ceramic, CoFe2O4, targets. X-ray diffraction (XRD) and Rutherford spectrometry (RBS) in random and channeling configuration have been used to determine the epitaxial relationship CoFe2O4 [100]/TiN [100]/Si [100]. Mössbauer spectroscopy, in combination with XRD and RBS, has been used to determine the composition and structure of the cobalt ferrite thin films. The TiN buffer layer induces a compressive strain in the cobalt ferrite thin films giving rise to an in-plane magnetic anisotropy. The degree of in-plane anisotropy depends on the lattice mismatch between CoFe2O4 and TiN, which is larger for CoFe2O4 thin films grown on the reactive sputtering process with ceramic targets.

Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2

Ferromagnetic van der Waals (vdW) materials are in demand for spintronic devices with all-two-dimensional-materials heterostructures. Here, we demonstrate mechanical exfoliation of magnetic-atom-intercalated transition metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such intercalated materials were thought difficult to exfoliate. Magnetotransport in exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering below its Curie temperature TC ~ 110 K as well as strong in-plane magnetic anisotropy; these are identical to its bulk properties. Further, van der Waals heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing possible spin injection and detection with these exfoliatable ferromagnetic materials through the vdW junction.

Magnetic behaviour of as-deposited and rapid thermal annealed Pr-Fe thin films

In the present work structure, microstructure and magnetic behaviour of e-beam evaporated Pr-Fe thin films was investigated in as-deposited and rapid thermal annealed conditions. The films were deposited on Si 〈100〉 substrates at room temperature. Structural studies carried out employing X-ray diffraction indicated that the as-deposited films were completely amorphous in nature. Upon rapid thermal annealing, presence of Fe phase could be observed from the X-ray diffraction patterns. Field emission gun scanning electron microscopy studies confirmed the presence of Fe nano-crystalline grains surrounded by amorphous Pr-Fe matrix with the number of nucleation sites increasing with increasing annealing temperature. Magnetization studies showed weak ferromagnetic behaviour for the as-deposited films whereas rapid thermal annealed films exhibited strong in-plane magnetic anisotropy owing to the presence of Fe nano-crystalline grains. Saturation magnetization estimated from the in-plane magnetization curves was found to increase with increasing annealing temperature up to 450°C although with further increase in annealing temperature to 550°C it decreased. A minimum coercivity of about 1.6kA/m was observed for the Pr-Fe film annealed at 450°C. Magnetostriction measurements indicated increase in magnetostriction with increasing annealing temperature up to 450°C. A maximum magnetostriction of about 100μ-strains was achieved for the film annealed at 450°C.

Magnetization and anomalous Hall effect in SiO2/Fe/SiO2 trilayers

SiO2/Fe/SiO2 sandwich structure films fabricated by sputtering were studied by varying the Fe layer thickness (tFe). The structural and microstructural studies on the samples showed that the Fe layer has grown in nanocrystalline form with (1 1 0) texture and that the two SiO2 layers are amorphous. Magnetic measurements performed with the applied field in in-plane and perpendicular direction to the film plane confirmed that the samples are soft ferromagnetic having strong in-plane magnetic anisotropy. The temperature dependence of magnetization shows complex behavior with the coexistence of both ferromagnetic and superparamagnetic properties. The transport properties of the samples as studied through Hall effect measurements show anomalous Hall effect (AHE). An enhancement of about 14 times in the saturation anomalous Hall resistance () was observed upon reducing the tFe from 300 to 50 Å. The maximum value of = 2.3 Ω observed for tFe = 50 Å sample is about 4 orders of magnitude larger than that reported for bulk Fe. When compared with the single Fe film, a maximum increase of about 56% in the was observed in sandwiched Fe (50 Å) film. Scaling law suggests that the Rs follows the longitudinal resistivity (ρ) as, , suggesting side jump as the dominant mechanism of the AHE. A maximum enhancement of about 156% in the sensitivity S was observed.

Magnetic properties and high frequency characteristics of FeCoN thin films

(Fe65Co35)N soft magnetic thin films were prepared by reactive RF magnetron sputtering with the sputtering power of 100 W on thermally oxidized Si substrate in various nitrogen partial pressures (PN2). A strong uniaxial in-plane magnetic anisotropy with the easy-axis coercive field as low as 1∼2 Oe was observed in films grown at PN2 in the range from 3.3% to 5.5%. The saturation magnetizations for those films were about 20 KG. Outside this range, almost isotropic magnetization curves were observed. Vector network analyzer and grounded coplanar waveguide were used to measure the ferromagnetic resonance (FMR) signals up to 25 GHz. The FMR signals were detected only in anisotropic films and their FMR frequencies were well fit to the Kittel formula. The obtained g-values and damping parameters at magnetic fields >20 kOe for films grown at PN2 of 3.3%, 4.8% and 5.5% were 1.96, 1.86, 1.92 and 0.0055, 0.0047, 0.0046, respectively. This low damping factor qualifies FeCoN thin films for high-frequency applications.

Anomalies in hysteresis properties of Fe20Ni80/Tb-Co films with unidirectional anisotropy

Specific features of magnetization process in permalloy soft magnetic layer exchange coupled to an amorphous ferrimagnetic Tb-Co layer with strong in-plane magnetic anisotropy were investigated. Anomalous large variations in coercivity Hc and unidirectional anisotropy field He versus temperature T and annealing temperature Ta dependencies were observed. The changes in Hc and He were shown to be reversible for temperature range 5–300K and irreversible for annealing temperatures 400–650K. A critical role of a nonmagnetic spacer in the Нс(Т) and Нe(Т) formation were demonstrated. In conclusion simple explanation based on an assumption of thermally-induced variation of the interlayer magnetic boundary position and interdiffusion process was proposed.

Enhancement of in-plane magnetic anisotropy in (111)-oriented Co0.8Fe2.2O4 thin film by deposition of PZT top layer

The CoFe2O4 and Co0.8Fe2.2O4 single layer (CFO) as well as PZT/CoFe2O4 and PZT/Co0.8Fe2.2O4 bilayer thin films were grown using the pulsed laser deposition technique on Pt(111)/Si substrates at 600 °C. All films had a perfect (111)-orientation and the degree of orientation of CFO films was improved by the deposition of a PZT top layer. Precision X-ray diffraction analysis (avoiding the shift of peaks due to sample misalignment) revealed that the CFO films on Pt(111)/Si substrate were under an out-of-plane contraction and the deposition of a PZT top layer led to the increase in the out-of-plane contraction. The (111)-oriented CFO single layer films had a strong in-plane magnetic anisotropy as a result of orientation as well as the stress-induced magnetic anisotropy. The magnetic properties of CFO film were altered by the deposition of a PZT top layer leading to the enhancement of in-plane magnetic anisotropy. The enhanced in-plane magnetic anisotropy was more detectable in PZT/Co0.8Fe2.2O4 rather than PZT/CoFe2O4 bilayer film, which could be expected from its higher magnetocrystalline as well as magnetostriction constants.

(111)-Oriented Co0.8Fe2.2O4+δ thin film grown by pulsed laser deposition: structural and magnetic properties

The perfect (111)-oriented Co0.8Fe2.2O4+δ thin films were grown on Pt(111)/Si substrate by pulsed laser deposition technique. Co0.8Fe2.2O4+δ film grown at oxygen pressure of 10 mTorr (optimum condition) has the highest (111)-orientation degree, the lowest surface roughness, uniformly compacted nanosize grain-feature structure (50–80 nm), and the highest magnetization. The Fe K-edge X-ray absorption near edge structure analyses revealed that, in Fe-doped CoFe2O4 film, the Fe also exists as Fe3+ (Co0.8Fe2.2O4+δ), which affects the lattice parameter as well as magnetic properties. The magnetic properties (saturation magnetization, coercivity, and squareness) of Co0.8Fe2.2O4+δ thin film are significantly higher than those of CoFe2O4 film. Moreover, the (111)-oriented Co0.8Fe2.2O4+δ thin film demonstrates strong in-plane magnetic anisotropy, which results from orientation, as well as the stress-induced magnetic anisotropy.

Strong in-plane magnetic anisotropy in (111)-oriented CoFe2O4 thin film

The perfect (111)-oriented CoFe2O4 thin films were grown on Pt(111)/Si substrate by pulsed laser deposition technique at substrate temperature of 600°C. The optimum oxygen pressure was found to be 10mTorr based on structural and magnetic properties. The film grown at 10mTorr has the highest (111)-orientation degree and magnetization. The films are under in-plane tensile stress due to the residual thermal strain which is thickness-dependent. It was found that the (111)-oriented CoFe2O4 thin film demonstrates the strong in-plane magnetic anisotropy which results from orientation as well as the stress-induced magnetic anisotropy.