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Perpendicularly magnetized films exhibiting small saturation magnetizations ( M s ) are essential for spin-transfer-torque magnetoresistive random access memories (MRAMs). In this study, the intermetallic compound (Mn–Cr)AlGe with a Cu2Sb crystal structure was investigated as a material exhibiting low M s (∼ 300 kA/m) and high-perpendicular magnetic anisotropy energy ( K u ). The layer thickness dependence of K u and effects of Mg-insertion layers at the top and bottom (Mn–Cr)AlGe|MgO interfaces were studied for film samples fabricated onto thermally oxidized silicon substrates to realize high K u values in the thickness range of a few nanometers. The values of K u were approximately 7 × 10 5 and 2 × 10 5 J/m3 at room temperature for 5 and 3 nm-thick (Mn–Cr)AlGe films, respectively, with an optimum annealing temperature of 400 °C and Mg-insertion thicknesses of 1.4 and 3.0 nm for the top and bottom interfaces, respectively. The Mg insertions were relatively thick compared with results of similar studies of the insertion effect on magnetic tunnel junctions. Cross-sectional transmission electron microscope images revealed that the Mg-insertion layers acted as barriers to the interdiffusion of Al atoms as well as oxidization from the MgO layers. The K u at a few-nanometer thicknesses was comparable to or higher than those reported for perpendicularly magnetized CoFeB films, which are conventionally used in MRAMs, whereas the M s value was one third or smaller than those of the CoFeB films. The developed (Mn–Cr)AlGe films are promising materials because of their magnetic properties and their compatibility to the silicon process in film fabrication. [ABSTRACT FROM AUTHOR]

Magnetic thin films showing high perpendicular magnetic anisotropy, Ku, and low saturation magnetization, Ms, are essential for realizing a small switching current in spintronic devices utilizing the current induced magnetization switching phenomena. The Cu2Sb-type MnAlGe intermetallic compound is a material showing uniaxial magnetocrystalline anisotropy with a relatively low Ms, which is attractive for spintronic application. In this study, the layer thickness dependence of Ku was investigated in poly-crystalline MnAlGe films, and the MgO template effect is discussed to achieve perpendicularly magnetized films in a few-nanometer thickness range. Experimental results suggested that the (001)-texture for the perpendicular magnetization was promoted by the MgO(001) template through the solid-phase epitaxy growth by annealing, which is similar with that in conventionally used CoFeB|MgO layered samples. Ku of about 2 × 106 erg/cm3 was achieved in a 5 nm-thick MnAlGe film using MgO buffer and capping exhibiting a low Ms value of approximately 200 emu/cm3 at room temperature. Although the magnitude of Ku is still in a moderate range, the low Ms is a promising feature for spintronic application. [ABSTRACT FROM AUTHOR]

A perpendicularly magnetized film is essentially important for spintronics applications, such as spin-transfer-torque type magnetoresistive random access memories, STT-MRAMs, and large perpendicular anisotropy energy, K u , with small saturation magnetization, M s , is required for reducing the critical current for the STT induced magnetization switching phenomenon. In this study, an equiatomic intermetallic compound, MnGaGe, was investigated in epitaxially grown film samples. Perpendicularly magnetized films with an M s value of about 260 emu/cm3 at 300 K were fabricated onto MgO (100) single crystal substrates. The maximum value of K u was 8.1 × 106 erg/cm3 at room temperature. Microstructure analysis using a scanning transmission electron microscope atomically revealed the Cu2Sb type crystal structure in the film sample. First principles calculations were also carried out to discuss the electronic structure. Using the analysis of the projected density of states for 3d-orbitals, the hybridization of the 3d-orbitals was suggested as a possible factor for promoting magnetocrystalline anisotropy. The MnGaGe film with the large K u and relatively small M s would be potentially used for spintronics applications. [ABSTRACT FROM AUTHOR]

Effects of metallic Mg insertion on tunnel magnetoresistance (TMR) effect were investigated in D022-Mn2.4Ga/Mg/MgO/CoFe magnetic tunnel junctions (MTJs). The thickness of Mg (dMg) was varied from 0 to 1.4 nm. TMR ratio exhibited maximum value of 22% with the dMg = 0.4 nm and a negative value of 14% with the dMg = 1.4 nm at 10 K. The dependence of resistance area products (R × A) on the dMg showed similar trend compared with those of what reported in conventional CoFeB-MgO based MTJs. Bias voltage dependences of differential conductance (dI/dV) and TMR ratio exhibited asymmetry with respect to the zero-bias. The difference of the zero-bias anomaly in the dI/dV spectra was also discussed, and an indication of reducing the inelastic tunneling process was found, implying the improvement of barrier/magnetic-layer interfaces by the Mg insertion. Considering a theoretical work done by Wang et al. [Phys. Rev. B 82, 054405 (2010)], the inversion of the sign and the asymmetric bias voltage dependence of TMR ratio were inferred to be attributed to the minority spin tunneling via a quantum well state in the thin metallic Mg layer between Mn2.4Ga and MgO. [ABSTRACT FROM AUTHOR]

We have investigated the exchange constant A (exchange stiffness D) and the magnetic anisotropy of Co2MnAlxSi1-x (CMAS) Heusler compounds as a function of the film composition. In case of Co2MnSi, A was found to be 23.5 pJ/m (D=5.86 meV nm2). Furthermore, A decreased with an increase in the Al content x. In the case of Co2MnAl, it was found to be 4.8 pJ/m (D=1.90 meV nm2). Finally, the cubic anisotropy constant K1 of CMAS films was found to be small (below 10 kJ/m3) and did not exhibit simple dependence on x. [ABSTRACT FROM AUTHOR]

Cu2Sb-type intermetallic compound, MnAlGe, is known to exhibit uniaxial magnetocrystalline anisotropy and relatively small saturation magnetization, which is suitable for spintronic application, e.g. spin-transfer phenomena requiring small critical current density. Ge-concentration dependence of the crystal structures, saturation magnetization, Ms, and perpendicular magnetic anisotropy, Ku was investigated for MnAlGe films prepared onto silicon substrates with a thermally oxidized amorphous layer. For the stoichiometric and Ge-rich samples, the films exhibited (001)-texture with perpendicular magnetization. The maximum values of Ms and Ku were 270 emu/cm3 and 4.8 × 106 erg/cm3, respectively, which were comparable values with those reported for bulk and epitaxially grown films in literatures. [ABSTRACT FROM AUTHOR]

Highlights • B2-Ni 2 MnAl/Fe showed the exchange bias shifts at low temperature. • The sign reversal of the exchange bias was observed due to the training effect. • The blocking temperature increased with the grain size controlled by annealing. • The largest exchange bias shift was 100 Oe at 10 K. • The highest blocking temperature was 200 K. Abstract The annealing effects on the exchange bias properties in antiferromagnetic Heusler alloy Ni 2 MnAl/Fe bilayers were investigated. Exchange bias shifts were observed at low temperatures. The sign reversal of the exchange bias shift was observed below the blocking temperature probably due to the training effect. The exchange bias shift showed a peak for the annealing temperature dependence, on the other hand, the blocking temperature increased with the annealing temperature, which closely correlates with the crystallographic grain size of the antiferromagnetic Ni 2 MnAl layer. [ABSTRACT FROM AUTHOR]

Highlights • Temperature dependence was investigated for Heusler CPP-GMR with ultra-thin inserts. • Anomalous temperature dependence was observed in Fe-insert junctions. • Mg-insert is proposed as a good diffusion barrier for the layered structure. Abstract Current-perpendicular-to-plane, CPP, giant magnetoresistance, GMR junctions attract interests for application of sensor devices, such as read head element of hard disk drives. Temperature dependence of the CPP-GMR effects was investigated, in this study, for junctions consisting of the half-metallic Heusler alloy, Co 2 (Fe-Mn)Si, electrodes and an L1 2 -type Ag 3 Mg spacer with the ultra-thin interface layers, Fe or Mg. For the Fe insert junctions, MR ratio exhibited local maximum at a temperature ranging from 50 K to 250 K which depends on the insertion thickness. The reason is unclear for the anomalous temperature dependence of the Fe junctions, however, a possibility is reduction of the Curie temperature for the Fe insert at the ultra-thin regime. On the other hand, MR ratios monotonically increased with decreasing the temperature for the Mg insert junctions, for which MR ratio of about 100% was observed at 10 K. Ratios of MR at 300 K to the low temperature are almost independent of the insertion thickness. Considering a fact that the shapes of MR curves nearly unchanged by the temperature change, it is suggested that the Mg insert works as a diffusion barrier at the Co 2 (Fe-Mn)Si/Ag 3 Mg interfaces. [ABSTRACT FROM AUTHOR]

Transport properties were investigated for epitaxial films of superconductor NbN and half-metallic Heusler alloy Co 2 MnSi under high magnetic fields up to 17 T. The superconducting transition temperature T c of NbN/Co 2 MnSi/Au trilayer films was determined to be 16.1 K in the absence of magnetic field. Temperature dependence of the resistivity ρ ( T ) was measured in both magnetic fields parallel and perpendicular to the surface of NbN/Co 2 MnSi/Au trilayer films. The activation energy U 0 ( H ) for vortex motion of the trilayer films in both magnetic fields was well fitted above 5 T by the similar model with the exponents in the field dependence of the pinning force density. From the resistivity ρ ( T ) measurements under high magnetic fields, the upper critical field H c 2 ( 0 ) at 0 K was also deduced to be μ 0 H c 2 ∥ ( 0 ) = 23.2 T for the parallel magnetic filed and μ 0 H c 2 ⊥ ( 0 ) = 15.8 T for the perpendicular magnetic field, respectively. The experimental results under magnetic fields revealed the superconductivity of the NbN layer was affected by the interplay between the superconducting NbN layer and the half-metallic Co 2 MnSi layer. [ABSTRACT FROM AUTHOR]

Buffer layer dependence of tunnel magnetoresistance (TMR) effects was investigated in Co2Fe0.4Mn0.6Si (CFMS)/MgO/Co50Fe50 magnetic tunnel junctions (MTJs). Pd, Ru and Cr were selected for the buffer layer materials, and MTJs with three different CFMS thicknesses (30, 5, and 0.8 nm) were fabricated. A maximum TMR ratio of 136% was observed in the Ru buffer layer sample with a 30-nm-thick CFMS layer. TMR ratios drastically degraded for the CFMS thickness of 0.8 nm, and the values were 26% for Cr buffer layer and less than 1% for Pd and Ru buffer layers. From the annealing temperature dependence of the TMR ratios, amounts of interdiffusion and effects from the lattice mismatch were discussed. [ABSTRACT FROM AUTHOR]

Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effects are of interest in a possible application of magnetic sensor elements, such as read-head of hard disk drives. To improve the junction performance, the interface tailoring effects were investigated for the Heulser alloy, Co2Fe0.4Mn0.6Si (CFMS), based CPP-GMR junctions with an L12-Ag3Mg ordered alloy spacer. Ultra-thin Fe or Mg inserts were utilized for the CFMS/Ag3Mg interfaces, and CPP-GMR at low bias current density, J and the J dependence were evaluated for the junctions. Although, at low bias J, MR ratio decreased with increasing the inserts thickness, the device output at high bias J exhibited quite weak dependence on the insert thickness. The output voltages of the order of 4 mV were obtained for the junctions regardless of the insert at an optimal bias J for each. The critical current density Jc was evaluated by the shape of MR curves depending on J. Jc increased with the insert thicknesses up to 0.45 nm. The enhancement of Jc suggests that spin-transfer-torque effect may reduce in the junctions with inserts, which enables a reduction of noise and can be an advantage for device applications. [ABSTRACT FROM AUTHOR]

Buffer-layer dependences of dead-layer thickness, saturation magnetization ( M\mathrm {s}) , and interface magnetic anisotropy ( K\mathrm {s}) were systematically investigated for Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy ultrathin films with Pd, Ru, and Cr buffer layers. Perpendicular magnetization was only achieved in 0.6 and 0.8 nm-thick CFMS ultrathin films deposited on Pd buffer layer and annealed at 400 °C. At the optimum annealing temperature of 400 °C, K\mathrm {{s}} of 1.2 erg/cm2 was obtained for the Pd buffer layer, which was 3–6 times larger than those for Ru and Cr buffer layers. The difference in K\mathrm {{s}} probably originates from the interdiffusion and different crystallized compounds at the interface between Pd (Ru, Cr) and CFMS layers. [ABSTRACT FROM AUTHOR]

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) heterostructures were fabricated using half-metallic Co2Fe0.4Mn0.6Si (CFMS) ferromagnetic electrodes and dual Ag-Mg spacers. The magnetic properties and (001)-epitaxial growth of the CFMS films were investigated in the whole CPP-GMR stacks. A large intrinsic CPP-GMR ratio of 73% (observed CPP-GMR value: 63%) at room temperature was achieved in the nanopatterned CPP-GMR junctions. The change in resistance-area product (ΔRA) value of the junctions was enhanced to 27 mΩ.μm². The large CPP-GMR effect in the dual-type CPP-GMR heterostructures could be attributed to their enhanced interfacial spin asymmetry scattering owing to the increased CFMS/Ag-Mg interfaces. The temperature dependence of the CPP-GMR effect was also studied, and a local maximum CPPGMR ratio of 175% with a ΔRA value of 47 mΩ.μm2 was observed at low temperatures. This work indicates that the dual-type CPP-GMR devices made up of CFMS electrodes and Ag-Mg spacers could be promising for future spintronic applications. [ABSTRACT FROM AUTHOR]

Film thickness, composition, and buffer layer dependences of perpendicular magnetic anisotropy (PMA) were investigated for ultrathin Co2FexMn1−xSi Heusler alloy films. The perpendicular magnetization was achieved when the thickness of the Co2MnSi on the Pd buffer layer was 0.6 and 0.8 nm. For Co2FeSi, only a 0.6 nm thick film exhibited perpendicular magnetization. Effective uniaxial magnetic anisotropy energy (K \(_{\rm u}^{\rm eff}\) ) was 1– \(2\,\times \, 10^{6}\) erg/cm \(^{3}\) . From the buffer layer dependence, it was revealed that perpendicular magnetization of Co2FeSi films was not achieved for a MgO or Cr buffer layer. These results imply that contributions from the Pd/Heusler alloy interface plays an important role in the PMA of ultrathin Co2FexMn1−xSi Heusler alloy films. [ABSTRACT FROM AUTHOR]

Superconducting properties were investigated in epitaxially layered films consisting of superconductor NbN and half-metallic Heusler alloy Co2MnSi (CMS). Temperature dependence of the electrical resistivity ρ(T) was measured by applying perpendicular magnetic fields to the surface of NbN/CMS films. With the increase of the CMS thickness dCMS, the upper critical field μ0Hc2 decreased monotonically, but the superconducting transition temperature Tc had the minimum of 10.1 K at dCMS ≈ 5 nm. The Tc behavior was in qualitative agreement with the theory of the π-coupling. The pair-breaking parameter δ determined by the superconducting fluctuation theory took the maximum at dCMS = 3 ∼ 5 nm, which would be related to the minimum of Tc. The experimental results reveal that the superconductivity of the NbN layer in NbN/CMS films is affected by the interplay between the superconducting NbN layer and the half-metallic CMS layer. [ABSTRACT FROM AUTHOR]

The anisotropic magnetoresistance (AMR) effect was investigated in epitaxially grown cobalt-based Heusler thin films of Co2(Fe–Mn)Si, Co2(Fe–Mn)(Al–Si) (CFMAS), and Co2(Fe–Mn)Al. Films were successfully fabricated onto MgO (100) single crystal substrate with an L21 ordering. The signs of the AMR ratio were negative for all the samples in this paper, which implies a possibility of half-metallic electronic structure. The maximum value of AMR ratio for the CFMAS film was −0.19% at 10 K, which is comparable with the earlier works on half-metallic Heusler alloys thin films. Our results propose that the CFMAS is also a good candidate for the spintronic devices, such as giant MR junctions. [ABSTRACT FROM AUTHOR]

Heusler alloys are a material class exhibiting various magnetic properties, including antiferromagnetism. A typical application of antiferromagnets is exchange bias that is a shift of the magnetization curve observed in a layered structure consisting of antiferromagnetic and ferromagnetic films. In this study, a layered sample consisting of a Heusler alloy, Mn 2 VAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered Mn 2 VAl is known as a ferrimagnet, with an optimum fabrication condition for the Mn 2 VAl layer, the Mn 2 VAl/Fe layered structure exhibits exchange bias. The appearance of the antiferromagnetic property in the Mn 2 VAl is remarkable; however, the details have been unclear. To clarify the microscopic aspects on the crystal structures and magnetic moments around the Mn 2 VAl/Fe interface, cross-sectional scanning transmission electron microscope (STEM) observation, and synchrotron soft X-ray magnetic circular dichroism (XMCD) measurements were employed. The high-angle annular dark-field STEM images demonstrated clusters of Mn 2 VAl with the L2 1 phase distributed only around the interface to the Fe layer in the sample showing the exchange bias. Furthermore, antiferromagnetic coupling between the Mn- and Fe-moments were observed in element-specific hysteresis loops measured using the XMCD. The locally ordered L2 1 phase and antiferromagnetic Mn-moments in the Mn 2 VAl were suggested as important factors for the exchange bias. [ABSTRACT FROM AUTHOR]

Epitaxial thin films of Mn3-xCoxGa were grown on MgO by magnetron co-sputtering with different Co content. Dependent on the Co content tetragonal or cubic structures are obtained. The composition dependence of saturation magnetization MS and uniaxial magnetic anisotropy Ku in the epitaxial films were investigated. A high magnetic anisotropy Ku of 1.2 MJ m-3 was achieved for the Mn2.6Co0.3Ga1.1 film with low magnetic moment of 0.84 μB. The valence band spectra of the films were investigated mainly by hard x-ray photoelectron spectroscopy. The evidence of sharp states in the cubic case, which are smeared out in the tetragonal case, proof the existence of a van Hove singularity that causes a band Jahn-Teller effect accompanied by a tetragonal distortion. These differences are in well agreement to the ab-initio calculations of the electronic structure. [ABSTRACT FROM AUTHOR]

The composition dependence of the tunnel magnetoresistance (TMR) effect in Mn-Ga/MgO/CoFe magnetic tunnel junctions (MTJs) for Mn54Ga46, Mn62Ga38, and Mn71Ga29 (at. %) electrodes was investigated. An MTJ with a Mn62Ga38 electrode showed a maximum TMR ratio of 23% at 10 K and high annealing endurance up to 375 °C. The bias voltage dependence of the TMR ratio was distinct among MTJs with different Mn-Ga compositions. Here, we discuss this dependence on the basis of the difference in the Δ1 band dispersions for Mn-Ga alloys calculated by first principles. [ABSTRACT FROM AUTHOR]

Epitaxially grown Mn2VAl films were fabricated on MgO (001) single crystalline substrates by using a sputtering technique. The resulting Mn2VAl films with substrate temperatures of Ts=500 and 600 °C showed an L21-ordered structure. The saturation magnetization was 150 emu/cm3 at 300 K for a sample with Ts=600 °C. Ferrimagnetic coupling between the Mn and V magnetic moments in the L21-Mn2VAl film was clearly demonstrated by soft x-ray magnetic circular dichroism. In previous studies, this coupling was found only in polycrystalline bulk samples examined by nuclear magnetic resonance. [ABSTRACT FROM AUTHOR]

Transport properties in magnetic tunnel junctions (MTJs) with Co2FexMn1-xSi (CFMS, x=0–1.0)/Al–O/Co75Fe25 structure and Gilbert damping constant in the epitaxial CFMS films were investigated. The tunnel magnetoresistance ratio is as high as 75% in MTJs with x=0.6 at room temperature. The Gilbert damping constant is minimal at x=0.4. Relations between half-metallicity and the Gilbert damping constant in CFMS films were examined, revealing that the damping constant is small in half-metallic CFMS films. [ABSTRACT FROM AUTHOR]

• Overview for the study on Heusler alloy based CPP-GMR was presented. • Spin asymmetry coefficients of L1 2 -Ag 3 Mg spacer junctions were quantitatively discussed. A half-metal is an ideal spin source to realize extremely large magnetoresistance effects because of the completely spin-polarized density of states at the Fermi level, and Heusler alloy is a material class for which several compositions are known to exhibit half-metallic properties. Current perpendicular-to-plane (CPP) giant magnetoresistance (GMR) effect is a resistance change that depends upon the relative angle of the magnetization vectors in magnetic layers separated by thin non-magnetic layer(s), which can be utilized for magnetic sensor applications. Over the last decade, the resistance change of CPP-GMR has been found to enhance greatly when using half-metallic Heusler alloys. In this article, the history of Heusler alloy based CPP-GMR is briefly reviewed, including the authors' recent results on the analysis of the spin asymmetry coefficients based on the Valet-Fert model. Finally, the degradation of half-metallic spin polarization at interfaces is discussed and a future prospect is described. [ABSTRACT FROM AUTHOR]

We demonstrate that the spin-Seebeck effect can be used to estimate the volume of edge domains formed in a giant magnetoresistive (GMR) device. The thermal gradient induced by Joule heating can be harnessed by the addition of a ferromagnetically insulating channel of Fe2O3 on the sides of the GMR pillar. This generates a spin wave in Fe2O3, which couples with the free-layer edge magnetization and controls the reversal of the ferromagnetic layers in one direction only, increasing the current density from (1.1 ± 0.1) × 107 A/cm2 to (7.0 ± 0.5) × 10 7 A/cm2. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be 10%–15% by spin-transfer torque. [ABSTRACT FROM AUTHOR]

We investigated the spin polarization P of Co-based Heusler alloy Co2FeSi by epitaxial contact Andreev reflection (ECAR) spectroscopy using epitaxially grown superconductor NbN and Heusler alloy Co2FeSi layered devices. Ferromagnetic Co2FeSi possesses the highest Curie temperature (TC ≈ 1100 K) and the largest spontaneous magnetic moment (ps ≈ 6 μB) in the class of Heusler alloys. The ECAR measurements revealed that the P value of Co2FeSi was 54 ± 2% with a finite barrier parameter Z, indicating that an intrinsic P value in ECAR spectroscopy would exceed reported values in point-contact Andreev reflection spectroscopy. We therefore established not only the epitaxial integration of ferromagnetic Co2FeSi with superconductor NbN on an MgO substrate but also the fabrication and evaluation techniques of their ECAR devices. This highly versatile superconducting spintronic system enables fundamental superconducting spintronic studies, and it is also a candidate for practical superconducting spintronic devices. [ABSTRACT FROM AUTHOR]

We report on the large anomalous Hall effect (AHE) and its structural-order dependence for epitaxial Co2MnGa topological semimetal films fabricated by a sputtering method. The structural orders of the films were systematically changed from B2 to L21 upon tuning the film growth temperature. It was found that the AHE was dramatically enhanced when the Co2MnGa films contained the L21-ordered phase. A large anomalous Hall angle of ∼12.6% at 10 K (∼11% at 300 K) was achieved at maximum. The dependence of anomalous Hall conductivity on longitudinal conductivity suggests that the intrinsic contribution plays a major role in the AHE. Thus, the enhanced AHE with the L21 order is attributed to the improvement of topological electronic structures in the L21-ordered Co2MnGa films. This scenario also allows us to explain the structural-order dependence of magnetoresistance. [ABSTRACT FROM AUTHOR]

• FeCo-BaF 2 granular films were prepared on glass substrates by tandem sputtering. • A huge Faraday rotation angle of −2.3 deg./μm was obtained in the FeCo-BaF 2 film. • m orb / m spin eff values were evaluated as 0.43 for Fe and 0.24 for Co using XMCD. • The giant Faraday effect is attributed to the enhancement of m orb. FeCo-insulator fluoride nanogranular films belong to an excellent material group that exhibits a huge Faraday effect, which is several times larger than those of conventional materials, in the optical communication wavelength band (1310 ∼ 1550 nm). In this study, FeCo-BaF 2 granular films were prepared on glass substrates by a tandem sputtering method. The Faraday effect was measured and a huge Faraday rotation angle of −2.3 deg./μm was observed for the wavelength of 1550 nm. The ratio of orbital magnetic moment to effective spin magnetic moment (m orb / m spin eff) was evaluated by x-ray magnetic circular dichroism (XMCD) measurements, and was found to be 0.43 for Fe and 0.24 for Co. The obtained values are several times larger than those of Fe-Co bulk samples. The elemental selectivity of the XMCD measurements reveals that Fe has a larger m orb / m spin eff value than that of Co. Such an increase in m orb is attributed to the reduction of the symmetry at the interface between FeCo and BaF 2 in the granular film, and is thought to be the origin of the giant Faraday effect in FeCo-fluoride granular films. [ABSTRACT FROM AUTHOR]

We model the charge, spin, and heat currents in ferromagnetic metaljnormal metaljnormal metal trilayer structures in the two current model, taking into account bulk and interface thermoelectric properties as well as Joule heating. The results include the temperature distribution as well as resistance-current curves that reproduce the observed shifted parabolic characteristics. Thin tunneling barriers can enhance the apparent Peltier cooling. The model agrees with the experimental results for wide multilayer pillars, but the giant effects observed for diameters ≲100 nm are still under discussion. [ABSTRACT FROM AUTHOR]

In order to enhance the magnetoresistance (MR) of perpendicular magnetic tunnel junctions (pMTJs) based on MnGa alloys, a single ferromagnetic layer such as Fe and Co was previously inserted between MnGa and MgO barrier. In this study, to further enhance the spin-filter effect, we introduced a Fe/Co bilayer as an interlayer in the MnGa/MgO interface. Compared to the single Co interlayer, an apparent MR ratio enhancement was obtained when Fe layer thickness was around 0.3 nm for pMTJs with MnGa compositions of Mn57Ga43, Mn62Ga38, and Mn70Ga30, and the maximum MR ratio reaches 50% at room temperature. In addition, inverted magnetoresistance loops were observed due to the antiparallel alignment of the magnetic moments of Co and MnGa layers separated by the thin Fe layer. [ABSTRACT FROM AUTHOR]

The perpendicular magnetic anisotropy (PMA) of cobalt (0.5-1.8 nm) films capped separately by pentacene (Pc), fullerene (C60), and 8-hydroxyquinoline-aluminum (Alq3) are investigated. For all three series, the thickness of Co is around 0.7 nm for maximum out-of-plane coercivity. It is found that the coercivity of C60-capped films is nearly equal to that for Alq3-capped samples, although both are smaller than for Pc-capped films. The different interface effects of Co/molecules are discussed to explain this observation. This work highlights the PMA of ferromagnetic metal, which can be markedly infected depending on the nature of organic molecule. [ABSTRACT FROM AUTHOR]

Organic spin valve devices with Co/Al2O3/8-hydroxyquinoline-aluminum (Alq3)/Co sandwich structure were fabricated and studied. Spin transport properties in the devices were investigated by measuring the current-voltage behavior and magnetoresistance (MR) at low temperature. With Al2O3 insertion, the relatively larger and positive MR ratio was observed with maximum value of around 19% at 5 K. The MR ratio was reduced with increasing temperature and finally disappeared above 80 K. In the case of devices without Al2O3 inserted layer, we have not observed MR at measured temperature. The role of Al2O3 inserted layer, spin transport mechanism, and the decrease of MR with increasing temperature in the organic spin valve were discussed. [ABSTRACT FROM AUTHOR]

The magnetic films of Co with Si/SiO2/Pt/Co/molecule structure were fabricated and their structural properties and magnetic anisotropy were investigated by varying both Co (0.5-1.8 nm) thickness and molecular capping layers of 5,6,11,12-tetraphenylnaphthacene (rubrene) and copper phthalocyanine (CuPc), respectively. The crystal structures were characterized using x-ray diffraction (XRD) and the magnetization curves were measured using vibrating sample magnetometer with an applied field both in parallel and perpendicular to a film plane. It was found that the thickness of Co for the maximum perpendicular magnetic anisotropy (PMA) is around 0.7 nm for both group films. However, the estimated effective magnetic anisotropy energy for Co was 2.9 ± 0.3 × 106 erg/cc for rubrene-capped sample, which was smaller than the value of 4.9 ± 0.4 × 106 erg/cc for CuPc-capped sample. The XRD patterns showed the crystal structure of rubrene layer was of amorphous structure and CuPc layer was polycrystalline. The different interface effects of Co/CuPc and Co/rubrene were discussed to analyze the change of PMA. [ABSTRACT FROM AUTHOR]

Spectral ellipsometry is a useful technique allowing fast, nondestructive, and contactless characterization of thin films and constituent materials. In this Letter, we show that both the linear magneto-optic Kerr effect (LinMOKE, proportional to the magnetization M) and the quadratic MOKE (QMOKE, proportional to M 2 ) can be a useful extension of spectral ellipsometry and are able to sense the crystallographic ordering of Heusler compounds. This is demonstrated for the Heusler compound Co2MnSi, which has a crystallographic transition from a B2 to an L21 structure with increasing annealing temperature Ta. We investigated a set of Co2MnSi thin films deposited on MgO(001) substrates and annealed from 300 to 500 °C. The amplitude of LinMOKE and QMOKE spectra, detected in the extended visible spectral range of 0.8–5.5 eV, scales linearly with Ta, and this effect is pronounced at the resonant peaks of the QMOKE spectra below 2.0 eV. Furthermore, the spectra of the magneto-optic (MO) parameters, which fully describe the MO response of Co2MnSi up to the second order in M, are obtained depending on Ta. Finally, the spectra are compared with ab initio calculations of a purely L21-ordered Co2MnSi Heusler compound. [ABSTRACT FROM AUTHOR]

Quadratic magneto-optical Kerr effects (QMOKE) are investigated in epitaxial Co2MnSi thin films as a function of the post-deposition annealing temperature. We determine the amplitude of the QMOKE signal for different annealing temperatures, which provide various degrees of L21 crystal ordering, as manifested by X-ray diffraction. We observe that QMOKE is significantly present only when the L21 ordering phase is also present, and that the QMOKE signal increases with the higher degree of L21 ordering. Additionally, we notice that the linear magneto-optical Kerr effect (LMOKE) decreases with higher annealing temperature. A comparison of the linear and quadratic MOKE contributions shows the amplitudes are of similar magnitude. From these results, we conclude that the presence of QMOKE is linked to the higher degree of L21 ordering in Co2MnSi. [ABSTRACT FROM AUTHOR]

• Current-induced crystallisation is demonstrated in a junction with epitaxially-grown Heusler alloy after post-annealing. • This can be applied for a conventional memory and sensor to improve their interfaces, which can reduce the junction resistance to mimic brain potentiation. • By combining this potentiation functionality with the neuromorphic operation, realistic synaptic computation can be developed. Recent development in neuromorphic computation allows us to achieve low power and highly efficient calculations better than the conventional von Neumann computation. In order to achieve realistic synaptic operation, potentiation to add weighting to strengthen a selected artificial synapse. Such functionality can be achieved by reducing the electrical resistance of the artificial synapse. Recently, a ferromagnetic Heusler alloy used in a magnetoresistive junction has been demonstrated to crystallise via the layer-by-layer mode by introducing an electrical current pulse. In this study, we have extended the current-induced crystallisation to a junction with epitaxially-grown Heusler alloy after post-annealing for crystallisation. By combining this potentiation functionality with the neuromorphic operation, realistic synaptic computation can be developed. [ABSTRACT FROM AUTHOR]

In this Note, we present a dual-beam magneto-optical Kerr effect (MOKE) magnetometer for the study of quadratic MOKE in magnetic thin films. The two beams simultaneously probe the sample, located in the middle of a quadrupole magnet, at two angles of incidence (0° and 45°). This combination of two systems allows one to automatically and routinely perform measurements that are sensitive to the combined longitudinal and quadratic MOKE signals (45°), or the quadratic effect alone (0°). Orientation-dependent and automated quantitative analyses of the quadratic effect’s amplitude are also implemented. We present representative measurements on Heusler compound thin films to illustrate the newly combined capabilities of this instrument. [ABSTRACT FROM AUTHOR]

Structural and magnetic properties of MnAl thin films with different composition, growth temperature, and post-annealing temperature were investigated. The optimum condition for fabrication of L10-MnAl perpendicularly magnetized thin film deposited on Cr-buffered MgO single crystal substrate was revealed. The results of x ray diffraction indicated that the MnAl films annealed at proper temperature had a (001)-orientation and L10-ordered structure. The L10-ordered films were perpendicularly magnetized and had a large perpendicular anisotropy. In addition, low surface roughness was achieved. For the optimized fabrication condition, the saturation magnetization Ms of 600 emu/cm3 and perpendicular magnetic anisotropy Ku of 1.0 × 107 erg/cm3 was obtained using the Mn48Al52 target at deposition temperature of 200 °C and post-annealing temperature of 450 °C. [ABSTRACT FROM AUTHOR]

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. Large VCMA coefficients of 108 and 139 fJ/Vm for the CFA film were achieved at room temperature and 4 K, respectively. The interfacial stability in the heterostructure was confirmed by repeating measurements. Temperature dependences of both the interfacial PMA and the VCMA effect were also investigated. It is found that the temperature dependences follow power laws of the saturation magnetization with an exponent of ~2, where the latter is definitely weaker than that of conventional Ta/CoFeB/MgO. The significant VCMA effect observed in this work indicates that the Ru/CFA/MgO heterostructure could be one of the promising candidates for spintronic devices with voltage control. [ABSTRACT FROM AUTHOR]