Epitaxial hcp Cobalt films with pronounced c-axis texture have been prepared by pulsed lased deposition (PLD) either directly onto Al2O3 (0001) single crystal substrates or with an intermediate Ruthenium buffer layer. The crystal structure and epitaxial growth relation was studied by XRD, pole figure measurements and reciprocal space mapping. Detailed VSM analysis shows that the perpendicular anisotropy of these highly textured Co films reaches the magnetocrystalline anisotropy of hcp-Co single crystal material. Films were prepared with thickness t of 20 nm < t < 100 nm to study the crossover from in-plane magnetization to out-of-plane magnetization in detail. The analysis of the periodic domain pattern observed by magnetic force microscopy allows to determine the critical minimum thickness below which the domains adopt a pure in-plane orientation. Above the critical thickness the width of the stripe domains is evaluated as a function of the film thickness and compared with domain theory. Especially the discrepancies at smallest film thicknesses show that the system is in an intermediate state between in-plane and out-of-plane domains, which is not described by existing analytical domain models.
The structures of epitaxial ultrathin Co2FeAl/MgO(001) heterostructures relating to the interface-induced perpendicular magnetic anisotropy (PMA) were investigated using scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray magnetic circular dichroism. We found that Al atoms from the Co2FeAl layer significantly interdiffuse into MgO, forming an Al-deficient Co-Fe-Al/Mg-Al-O structure near the Co2FeAl/MgO interface. This atomic replacement may play an additional role for enhancing PMA, which is consistent with the observed large perpendicular orbital magneti…
We investigated perpendicular magnetic anisotropy (PMA) and related properties of epitaxial Fe (0.7 nm)/MgAl2O4(001) heterostructures prepared by electron-beam evaporation. Using an optimized structure, we obtained a large PMA energy ~1 MJ/m3 at room temperature, comparable to that in ultrathin-Fe/MgO(001) heterostructures. Both the PMA energy and saturation magnetization show weak temperature dependence, ensuring wide working temperature in application. The effective magnetic damping constant of the 0.7 nm Fe layer was ~0.02 using time-resolved magneto-optical Kerr effect. This study demonstr…
A perpendicularly magnetized ferromagnetic layer is an important building block for recent/future highdensity spintronic memory applications. This paper reports on the fabrication of perpendicularly magnetized Ni / Pt superlattices and the characterization of their structures and magnetic properties. The optimization of film growth conditions allowed us to grow epitaxial Ni / Pt (001) superlattices on SrTiO$_{3}$ (001) single crystal substrates. We investigated their structural parameters and magnetic properties as a function of the Ni layer thickness, and obtained a high uniaxial magnetic ani…
Graphene is attractive for spintronics due to its long spin life time and high mobility. So far only thick and polycrystalline slabs have been used as ferromagnetic electrodes. We report the growth of flat, epitaxial ultrathin Co films on graphene. These display perpendicular magnetic anisotropy in the thickness range 0.5-1nm, which is confirmed by theory. PMA, epitaxy and ultrathin thickness bring new perspectives for graphene-based spintronic devices such as the zero-field control of an arbitrary magnetization direction, band matching between electrodes and graphene, and interface effects su…
Cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films are prepared on gadolinium gallium garnet (GGG) substrate with pulsed laser deposition (PLD). It is observed that the films grown on GGG(111) substrate exhibit perpendicular magnetic anisotropy (PMA) as compared to films grown on GGG(100) substrate. The developed PMA is confirmed from magneto-optical Kerr effect, bulk magnetization and ferromagnetic resonance measurements. Further, the magnetic bubble domains are observed in the films exhibiting PMA. The observations are explained in terms of the growth direction of Ce:YIG fi…
(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001) substrates by ion beam sputtering in order to determine the effect that the crystalline orientation of the NiO antiferromagnetic layer has on the magnetization curve of the NiFe ferromagnetic layer. Simple models predict no exchange anisotropy for the (001)-oriented surface, which in its bulk termination is magnetically compensated. Nonetheless exchange anisotropy is present in the epitaxial films, although it is approximately half as large as in polycrystalline films that were grown simultaneously. Experiments show that d…
We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a-c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a-c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence ma…
We demonstrate strain-tuning of magnetocrystalline anisotropy over a range of more than one thousand Gauss in epitaxial Y3Fe5O12 films of excellent crystalline quality grown on lattice-mismatched Y3Al5O12 substrates. Ferromagnetic resonance (FMR) measurements reveal a linear dependence of both out-of-plane and in-plane uniaxial anisotropy on the strain-induced tetragonal distortion of Y3Fe5O12. Importantly, we find the spin mixing conductance G_r determined from inverse spin Hall effect and FMR linewidth broadening remains large: G_r = 3.33 x 10^14 Ohm^-1m^-2 in Pt/Y3Fe5O12/Y3Al5O12 heterostru…
Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the central interests in spintronics applications. Here we report a giant Gilbert damping anisotropy in epitaxial Co$_{50}$Fe$_{50}$ thin film with a maximum-minimum damping ratio of 400 \%, determined by broadband spin-torque as well as inductive ferromagnetic resonance. We conclude that the origin of this damping anisotropy is the variation of the spin orbit coupling for different magnetization orientations in the cubic lattice, which is further corroborate from the magnitude of the anisotropic magnetoresistance in Co$_…
Temperature dependent magnetometry and transport measurements on epitaxial Fe3O4 films grown on BaTiO3(100) single crystals by molecular beam epitaxy show a series of discontinuities, that are due to changes in the magnetic anisotropy induced by strain in the different crystal phases of BaTiO3. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO3 at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magn…
Epitaxial self-assembled quantum dots (SAQDs) represent an important step in the advancement of semiconductor fabrication at the nanoscale that will allow breakthroughs in electronics and optoelectronics. In these applications, order is a key factor. Here, the role of crystal anisotropy in promoting order during early stages of SAQD formation is studied through a linear analysis of a commonly used surface evolution model. Elastic anisotropy is used a specific example. It is found that there are two relevant and predictable correlation lengths. One of them is related to crystal anisotropy and i…
MnxGa films with high perpendicular anisotropy, coercivity and energy product have great application potential in ultrahigh-density perpendicular recording, permanent magnets, spin-transfer-torque memory and oscillators, magneto-resistance sensors and ferromagnetic metal/semiconductor heterostructure devices. Here we present a comprehensive diagram of effective magnetism-tailoring of perpendicularly magnetized MnxGa films grown on III-V semiconductor GaAs by using molecular-beam epitaxy for the first time, by systematically investigating the wide-range composition and detailed post-growth anne…
We show tunable strain-induced perpendicular magnetic anisotropy (PMA) over a wide range of thicknesses in epitaxial ferrimagnetic insulator Eu3Fe5O12 (EuIG) and Tb3Fe5O12 (TbIG) thin films grown by pulsed-laser deposition on Gd3Ga5O12 with (001) and (111) orientations, respectively. The PMA field is determined by measuring the induced anomalous Hall loops in Pt deposited on the garnet films. Due to positive magnetostriction constants, compressive in-plane strain induces a PMA field as large as 32.9 kOe for 4 nm thick EuIG and 66.7 kOe for 5 nm thick TbIG at 300 K, and relaxes extremely slowly…
We show that the magnetic anisotropy in spinel-structure CoCr$_2$O$_4$ thin films exhibits a strain dependence in which compressive strain induces an out-of-plane magnetic easy axis and tensile strain an in-plane easy axis, exactly opposite to the behavior reported for the related compound CoFe$_2$O$_4$. We use density functional theory calculations within the LSDA+U approximation to reproduce and explain the observed behavior. Using second-order perturbation theory, we analyse the anisotropy tensor of the Co$^{2+}$ ions in both octahedral and tetrahedral coordination, allowing us to extend ou…
Single-crystal Heusler atomic-scale superlattices that have been predicted to exhibit perpendicular magnetic anisotropy and half-metallicity have been successfully grown by molecular beam epitaxy. Superlattices consisting of full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers with high cobalt or high iron concentrations for samples grown near room temperature on GaAs (001). Superlattice structures grown with an exce…
We report the magnetotransport properties of ferromagnet (FM)/antiferromagnet (AFM) Fe$_2$CrSi/Ru$_2$MnGe epitaxial bilayers using current-in-plane configurations. Above the critical thickness of the Ru$_2$MnGe layer to induce exchange bias, symmetric and asymmetric curves were observed in response to the direction of FM magnetocrystalline anisotropy. Because each magnetoresistance curve showed full and partial AFM rotation, the magnetoresistance curves imply the impact of the Fe$_2$CrSi magnetocrystalline anisotropy to govern the AFM rotation. The maximum magnitude of the angular-dependent re…
We present results on growth of large area epitaxial ReS2 thin film both on c plane sapphire substrate and MoS2 template by pulsed laser deposition (PLD). Films tend to grow with (0001) ReS2 perpendicular to (0001) Al2O3 and (0001) ReS2 perpendicular to (0001) MoS2 parallel to (0001) Al2O3 at deposition temperature below 300 deg C. Films are polycrystalline grown at temperature above 300 deg C. The smoothness and quality of the films are significantly improved when grown on MoS2 template compared to sapphire substrate. The results show that PLD is suitable to grow ReS2 epitaxial thin film over…
Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is a key technology for achieving energy-efficiency electronic devices with ultralow power consumption. Here, we report the first demonstration of the VCMA effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an effective voltage control on switching fields for the CFA free layer. A large VCMA coefficient of 108 (139) fJ/Vm for the CFA film was ach…
The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers grown by molecular beam epitaxy is studied by means of superconducting quantum interference device (SQUID) magnetometry as well as by ferromagnetic resonance (FMR) and magnetooptical effects. Experimental results are described considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude of cubic and uniaxial anisotropy constants is found to be proportional to the fourth and second power of saturation magnetization, respectively. Similarly to the case of (001) samples, the spin reorientation transitio…
We present a systematic study on the influence of epitaxial strain and hole concentration on the magnetic anisotropy in (Ga,Mn)As at 4.2 K. The strain was gradually varied over a wide range from tensile to compressive by growing a series of (Ga,Mn)As layers with 5% Mn on relaxed graded (In,Ga)As/GaAs templates with different In concentration. The hole density, the Curie temperature, and the relaxed lattice constant of the as-grown and annealed (Ga,Mn)As layers turned out to be essentially unaffected by the strain. Angle-dependent magnetotransport measurements performed at different magnetic fi…
Perpendicular magnetic anisotropy (PMA) energy up to $K_{\mathrm{u}}=6.1\pm0.8$ MJ m$^{-3}$ is demonstrated in this study by inducing large lattice-distortion exceeding 3% at room temperature in epitaxially distorted cobalt ferrite Co$ _{x} $Fe$ _{3-x} $O$ _{4} $ (x = 0.72) (001) thin films. Although the thin film materials include no rare-earth elements or noble metals, the observed $ K_{u} $ is larger than that of the neodymium-iron-boron compounds for high-performance permanent magnets. The large PMA is attributed to the significantly enhanced magneto-elastic effects, which are pronounced i…
We report the current-perpendicular-to-plane giant magnetoresistance of a spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu spacer layer despite the large lattice mismatch between Cu and CMS. The highest MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room …
For the magnetic shape memory effect, knowledge about the interaction between martensitic and magnetic domain structure is essential. In the case of Ni-Mn-Ga bulk material and foils, a staircase-like magnetic domain structure with 90°- and 180°-domain walls is known for modulated martensite. In the present paper we show that the magnetic domain pattern of thin epitaxial films is fundamentally different. Here we analyze epitaxial Ni-Mn-Ga films by atomic and magnetic force microscopy to investigate the correlation between the twinned martensitic variants and the magnetic stripe domains. The obs…
Strain engineering is a powerful mean for tuning the various functionalities of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials such as NdFeO3 (NFO) are of prime interest because of their intriguing magnetic properties as well as their technological potential applications especially as thin films. Here, using a large set of complementary and advanced techniques, we show that NFO epitaxial thin films, successfully grown by pulsed laser deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical thickness tc of 54 nm, associated with the occurrence of…
Perpendicular magnetic anisotropy was found to be highly sensitive to the nominal thickness and morphology of laterally heterogeneous CoPd films in the vicinity of the metal insulator transition. We used the effect to tune the anisotropy by the width of lithographically patterned stripes with non-uniform cross-sectional thickness profiles. The phenomenon and the method can be suitable to control the local anisotropy of spintronic logic circuitry elements by their shape and lateral dimensions.
In this work we are investigating the effect of strain in ultrathin Mn-Ga thin films on the magnetic properties at room temperature. Two different Mn-Ga compositions of which one is furthermore doped with Co were grown on Cr buffered MgO (001) substrates. Films with a thickness below 12nm are highly strained and it was observed that the ratio c/a vs. thickness is depending on composition. Using c/a as an order parameter the PMA is shown to be drastically reduced with increasing strain. These findings should be considered when generalizing and downscaling results obtained from films >20nm. Furt…
We investigate the magnetization reversal in Fe/MgO(001) films with fourfold in-plane magnetic anisotropy and an additional uniaxial anisotropy whose orientation and strength are tuned using different growth geometries and post growth treatments. The previously adopted mechanism of 180^{o} domain wall nucleation clearly fails to explain the observed 180^{o} magnetization reversal. A new reversal mechanism with two successive domain wall nucleations consistently predicts the switching fields for all field orientations. Our results are relevant for a correct interpretation of magnetization rever…
Magnetic properties of nanometer thick Co films intercalated at the graphene/Ir(111) interface are investigated using spin-polarized low-energy electron microscopy (SPLEEM) and Auger electron spectroscopy. We show that the graphene top layer promotes perpendicular magnetic anisotropy in the Co film underneath, even for relatively thick intercalated deposits. The magnetic anisotropy energy is significantly larger for the graphene/Co interface than for the free Co surface. Hybridization of the graphene and Co electron orbitals is believed to be at the origin of the observed perpendicular magneti…
We report perpendicular magnetic anisotropy in the ferromagnetic Heusler alloy Co$_2$MnGa in a MgO/Co$_2$MnGa/Pd trilayer stack for Co$_2$MnGa thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin reorientation transition from perpendicular to in-plane magnetic anisotropy which we study through the anomalous Hall effect. From the temperature dependence of the anomalous Hall effect, we observe the expected scaling of $ρ_{xy}^{AHE}$ with $ρ_{xx}$, suggesting the intrinsic and side-jump mechanisms are largely responsible for the anomalous Hall effect in this material.
We observe magnetic domain structures of MgO/CoFeB with a perpendicular magnetic easy axis under an electric field. The domain structure shows a maze pattern with electric-field dependent isotropic period. We find that the electric-field modulation of the period is explained by considering the electric-field modulation of the exchange stiffness constant in addition to the known magnetic anisotropy modulation.
An unusual crystallographic orientation of hexagonal Ru with a 4-fold symmetry emerging in epitaxial MgO/Ru/Co2FeAl/MgO heterostructures is reported, in which an approximately Ru(02-23) growth attributes to the lattice matching among MgO, Ru, and Co2FeAl. Perpendicular magnetic anisotropy of the Co2FeAl/MgO interface is substantially enhanced as compared with those with a Cr(001) layer. The MTJs incorporating this structure gave rise to the largest tunnel magnetoresistance for perpendicular MTJs using low damping Heusler alloys. The 4-fold-symmetry hexagonal Ru arises from an epitaxial growth …
Rare earth free alloys are in focus of permanent magnet research since the accessibility of the elements needed for nowadays conventional magnets is limited. Tetragonally strained iron-cobalt (Fe-Co) has attracted large interest as promising candidate due to theoretical calculations. In experiments, however, the applied strain quickly relaxes with increasing film thickness and hampers stabilization of a strong magnetocrystalline anisotropy. In our study we show that already 2 at% of carbon substantially reduce the lattice relaxation leading to the formation of a spontaneously strained phase wi…
The use of epitaxial layers for domain wall-based spintronic applications is often hampered by the presence of pinning sites. Here, we show that when depositing Mn4N(10 nm) epitaxial films, the replacement of MgO(001) by SrTiO3(001) substrates allows minimizing the misfit, and to obtain an improved crystalline quality, a sharper switching, a full remanence, a high anisotropy and remarkable millimeter-sized magnetic domains, with straight and smooth domain walls. In a context of rising interest for current-induced domain wall motion in rare
CuMnAs with perpendicular magnetic anisotropy is proposed as an active material for antiferromagnetic memory. Information can be stored in the antiferromagnetic domain state, while writing and readout can rely on the existence of the surface magnetization. It is predicted, based on first-principles calculations, that easy-axis anisotropy can be achieved in bulk CuMnAs by substituting a few percent of As atoms by Ge, Si, Al, or B. This effect is attributed to the changing occupation of certain electronic bands near the Fermi level induced by the hole doping. The calculated temperature dependenc…
The authors demonstrated that L21-ordered full-Heusler Co2FeSi (CFS) alloy film with thickness of 100 nm were formed by facing targets sputtering (FTS) method at a substrate temperature TS = 300 deg C. Degrees of L21- and B2- order for the film were 0.37, and 0.96, respectively. Furthermore, full-Heusler CFS alloy thin films with perpendicular magnetic anisotropy (PMA) induced by MgO-interface magnetic anisotropy were successfully formed by the FTS method. The CFS/MgO stacking layers showed PMA when dCFS was 0.6 nm <= dCFS <= 1.0 nm. The PMA in these structures resulted from the CFS/MgO interf…
We present a study of the dynamic magnetic properties of TiN-buffered epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series annealed at different temperatures are prepared and the magnetic damping is measured, a lowest value of $α=2.18\times 10^{-3}$ is obtained. The perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also characterized. The evolution of the interfacial perpendicular anisotropy constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and compared with the widely used CoFeB/MgO interface. A large volume contribution to the per…
Understanding the magnetic anisotropy at ferromagnetic metal/oxide interface is a fundamental and intriguing subject. Here we propose an approach to manipulate the strength of perpendicular magnetic anisotropy (PMA) by varying MgO thickness in the MgO/CoFeB/Ta thin films. We identify that the PMA at the MgO/CoFeB interface is tuned by the crystalline structure of bulk MgO layer and decreases dramatically due to the onset of crystalline MgO forming with the increase of MgO thickness. Our work opens an avenue to manipulate the magnetic anisotropy by the modification of the ferromagnetic metal/ox…
The tunability of Ar+ ion irradiation of Co/Pd multilayers has been employed to create depth-dependent perpendicular anisotropy gradients. By adjusting the Ar+ kinetic energy and fluence, the depth and lateral density of the local structural modification are controlled. First-order reversal curve analysis through X-ray magnetic circular dichroism and conventional magnetometry studies show that the local structural damage weakens the perpendicular anisotropy near the surface, leading to a magnetization tilting towards the in-plane direction. The ion irradiation method is complementary to, and m…
We investigate magnetic anisotropy and magnetization reversal mechanism in chromium telluride thin films grown by molecular beam epitaxy. We report existence of strong perpendicular anisotropy in these thin films, along with a relatively strong second order anisotropy contribution. The angular variation of the switching field observed from the magnetoresistance measurement is explained quantitatively using a one-dimensional defect model. The model reveals the relative roles of nucleation and pinning in the magnetization reversal, depending on the applied field orientation. Micromagnetic simula…
The Fe/MgO interface is an essential ingredient in spintronics as it shows giant tunneling magnetoresistance and strong perpendicular magnetic anisotropy (PMA). A recent study demonstrated that the insertion of an ultra-thin LiF layer between the Fe and MgO layers enhances PMA significantly. In this study, we perform x-ray magnetic circular dichroism measurements on Fe/LiF/MgO multilayers to reveal the origin of the PMA enhancement. We find that the LiF insertion increases the orbital-magnetic-moment anisotropy and thus the magnetic anisotropy energy. We attribute the origin of this orbital-ma…
We investigate in this paper the origin of perpendicular anisotropy in Co (1.6 nm)/Pt (3.0 nm) bilayers grown on alumina and annealed up to 650$^{\circ}$C. Above 350$^{\circ}$C, all layers exhibit perpendicular anisotropy. Then coercive fields increase linearly with annealing temperature following two different rates: 0.05 T/100$^{\circ}$C below 550$^{\circ}$C and 0.8 T/100$^{\circ}$C above. By making careful structural characterizations using x-ray diffraction and transmission electron microscopy, we demonstrate the presence of short range correlation of L1$_{1}$ type below 550$^{\circ}$C whe…
We present experimental control of the magnetic anisotropy in a gadolinium iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by simply changing the sample temperature. The magnetic hysteresis loops obtained by SQUID magnetometry measurements unambiguously reveal a change of the magnetically easy axis from out-of-plane to in-plane depending on the sample temperature. Additionally, we confirm these findings by the use of temperature dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to determine the effective magnetization, we utilize the intrinsic adva…
We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer. The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room temperature which increases to 14.7% at 4.2K. The layers show clear separate switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in the NiMnSb layer leads to different switching characteristics depending on the direction in which the magnetic field is applied, an effect which can be used for sensor applications.
Very high magnetic anisotropies have been theoretically predicted for strained Fe-Co(-X) and indeed several experiments on epitaxial thin films seemed to confirm strain induced anisotropy enhancement. This study presents a critical analysis of the different contributions to perpendicular anisotropy: volume, interface and surface anisotropies. Tracing these contributions, thickness series of single layer films as well as multilayers with Au-Cu buffers/interlayers of different lattice parameters have been prepared. The analysis of their magnetic anisotropy reveals a negligible influence of the l…
We report perpendicular magnetic anisotropy (PMA) in the half-metallic ferromagnetic Heusler alloy Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS) in a MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2 nm, with a magnetic anisotropy energy density of $K_U = 1.5\times 10^6$ erg/cm$^3$ for t$_{\tiny \textrm{CFMS}} = 1.5$ nm. Both the MgO and Pd layer are necessary to induce the PMA. We measure a tunable anomalous Hall effect, where its sign and magnitude vary with both the CFMS and Pd thickness.
We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO bilayers in contact with W, Ta, IrMn and Ti which has been suggested as the spin-orbit-torque-related underlayers. The saturation magnetization of the CoFeB depends on the underlayer materials due to formation of a dead-layer, affecting PMA strength of each film. The x-ray magnetic circular dichroism measurement reveals that the interfacial intermixing suppresses only the perpendicular orbital moment of Fe, while the intermixing simultaneously suppresses both the perpendicular and in-plane orbital moments of Co.
We investigated electronic structure and magnetic anisotropy in the Fe/MgO interface of magnetic metal and dielectric insulator under the Cr layer of small electronegativity, by means of the first-principles density functional approach. The result indicates that the interface resonance state gets occupied unlike a typical rigid band picture as the number of Fe layers decreases, finding large perpendicular anisotropies in the oscillating behavior for thickness dependence. We discuss scenarios of the two dimensional van Hove singularity associated with flat band dispersions, and also the accurac…
Co /CoO/Co polycrystalline film was grown on Si (001) substrate and magnetic properties have been investigated using in-situ magneto-optic Kerr effect during growth of the sample. Magnetic anisotropy with easy axis perpendicular to the film surface has been observed in top Co layer, whereas bottom layer was found to be soft with in-plane magnetization without any influence of top layer. Ex-situ in-plane and out-of-plane diffraction measurements revealed that the growth of Co on oxidized interface takes place with preferential orientation of c-axis perpendicular to the film plane, which results…
Ferromagnet/heavy metal (FM/HM) multilayer thin films with $C_{2v}$ symmetry have the potential to host antiskyrmions and other chiral spin textures via an anisotropic Dzyaloshinkii-Moriya interaction (DMI). Here, we present a candidate material system that also has a strong uniaxial magnetocrystalline anisotropy aligned in the plane of the film. This system is based on a new Co/Pt epitaxial relationship, which is the central focus of this work: hexagonal closed-packed Co$(10\bar{1}0)[0001]$ $\parallel$ face-centered cubic Pt$(110)[001]$. We characterized the crystal structure and magnetic pro…
High perpendicular magnetic anisotropy (PMA), a property needed for nanoscale spintronic applications, is rare in oxide conductors. We report the observation of a PMA up to 0.23 MJ/m3 in modestly strained epitaxial NiCo2O4 (NCO) films which are room-temperature ferrimagnetic conductors. Spin-lattice coupling manifested as magnetoelastic effect was found as the origin of the PMA. The in-plane xx-yy states of Co on tetrahedral sites play crucial role in the magnetic anisotropy and spin-lattice coupling with an energy scale of 1 meV/f.u. The elucidation of the microscopic origin paves a way for e…
Recently, perpendicular magnetic anisotropy (PMA) and its voltage control (VC) was demonstrated for Cr/Fe/MgO (Physical Review Applied 5, 044006 (2016)). In this study, we shed a light on the origin of large voltage-induced anisotropy change in Cr/Fe/MgO. Analysis of the chemical structure of Cr/Fe/MgO revealed the existence of Cr atoms in the proximity of the Fe/MgO interface, which can affect both magnetic anisotropy (MA) and its VC. We showed that PMA and its VC can be enhanced by controlled Cr doping at the Fe/MgO interface. For Cr/Fe (5.9 Å)/Cr (0.7 Å)/MgO with an effective PMA of 0.8 MJ/…
We report the compositional and temperature dependence of magnetic compensation in amorphous GdFeCo films. Magnetic compensation is attributed to the competition between antiferromagnetic coupling of rare-earth with transition-metal (TM) ions and ferromagnetic interaction between the TM ions. The low-Gd region from 20 to 34 at. % was found to exhibit compensation phenomena characterized by a low saturation magnetization and perpendicular magnetic anisotropy (PMA) near the compensation temperature. Compensation temperature was not observed in previously unreported high-Gd region from 52 to 59 a…
Domain structures in CoFeB-MgO thin films with a perpendicular easy magnetization axis were observed by magneto-optic Kerr-effect microscopy at various temperatures. The domain wall surface energy was obtained by analyzing the spatial period of the stripe domains and fitting established domain models to the period. In combination with SQUID measurements of magnetization and anisotropy energy, this leads to an estimate of the exchange stiffness and domain wall width in these films. These parameters are essential for determining whether domain walls will form in patterned structures and devices …
Multilayers of Co90Fe10/Pd with different bilayer thicknesses, have been deposited by dc-magnetron sputtering on thermally oxidized Si wafers. Transmission electron microscopy showed that the highly textured crystalline films had columnar structure, while scanning transmission electron microscopy and atomic force microscopy respectively indicated some layer waviness and surface roughness. The magnetic domain structure and perpendicular magnetic anisotropy (PMA) of the Co90Fe10/Pd multilayers were investigated by off-axis electron holography and magnetic force microscopy. The Co90Fe10 layer thi…
We carried out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy and investigated cation valence states and spin and orbital magnetic moments in the inverse-spinel ferrimagnet Ni$_{1-x}$Co$_{2+y}$O$_{4-z}$ (NCO) epitaxial films with the perpendicular magnetic anisotropy. We show that the oxygen pressure P$_{O2}$ during the film growth by pulsed laser deposition influences not only the cation stoichiometry (site-occupation) but also the cation valence state. Our XAS results show that the Ni in the O$_{h}$-site is in the intermediate valence state betw…
We have prepared the dilute magnetic semiconductor (DMS) InMnAs with different Mn concentrations by ion implantation and pulsed laser melting. The Curie temperature of the In1-xMnxAs epilayer depends on the Mn concentration x, reaching 82 K for x=0.105. The substitution of Mn ions at the Indium sites induces a compressive strain perpendicular to the InMnAs layer and a tensile strain along the in-plane direction. This gives rise to a large perpendicular magnetic anisotropy, which is often needed for the demonstration of electrical control of magnetization and for spin-transfer-torque induced ma…
