X-ray Magnetic Circular Dichroism Measurements Research Articles

Correlation of Interface Interdiffusion and Skyrmionic Phases.

Magnetic skyrmions are prime candidates for the next generation of spintronic devices. Skyrmions and other topological magnetic structures are known to be stabilized by the Dzyaloshinskii-Moriya interaction (DMI) that occurs when the inversion symmetry is broken in thin films. Here, we show by first-principles calculations and atomistic spin dynamics simulations that metastable skyrmionic states can also be found in nominally symmetric multilayered systems. We demonstrate that this is correlated with the large enhancement of the DMI strength due to the presence of local defects. In particular, we find that metastable skyrmions can occur in Pd/Co/Pd multilayers without external magnetic fields and can be stable even near room temperature conditions. Our theoretical findings corroborate with magnetic force microscopy images and X-ray magnetic circular dichroism measurements and highlight the possibility of tuning the intensity of DMI by using interdiffusion at thin film interfaces.

Ferromagnetism induced by hybridization of Fe 3d orbitals with ligand InSb bands in the n -type ferromagnetic semiconductor (In,Fe)Sb

Fe-doped III-V ferromagnetic semiconductor (FMS) (In,Fe)Sb is a promising material for spintronic device applications because of the n-type carrier conduction and the ferromagnetism with high Curie temperature (TC > 300 K). To clarify the mechanism of the high-TC ferromagnetism, we have investigated the electronic structure and magnetic properties of an (In,Fe)Sb thin film by performing x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at the Fe L2,3 edges. The magnetic-field dependence of the XMCD spectra reveals that there are ferromagnetic-like Fe and paramagnetic-like Fe components in the (In,Fe)Sb thin film. The XAS and XMCD spectra of the ferromagnetic-like and paramagnetic-like Fe components resemble those of other Fe-doped FMSs and extrinsic oxides, respectively. The finite value of the ratio between the orbital and spin magnetic moments estimated by applying the XMCD sum rules indicates that the valence state of the Fe ions substituting for the In sites in (In,Fe)Sb is not purely ionic Fe3+, but intermediate between Fe3+ and Fe2+. The qualitative correspondence between the magnetic-field dependence of the visible-light magnetic circular dichroism intensity and that of the XMCD intensity demonstrates that the Zeeman splitting of the InSb band is proportional to the net magnetization of the doped Fe. These results suggest that the ferromagnetism of (In,Fe)Sb originates from the Fe 3d orbitals hybridized with the host InSb bands.

Signatures of room-temperature magnetic glassiness in zinc ferrite epitaxial thin films

Zinc ferrite (${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$) epitaxial thin films were grown by reactive magnetron sputtering on ${\mathrm{MgAl}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ and ${\mathrm{Al}}_{\text{2}}{\mathrm{O}}_{\text{3}}$ substrates varying a range of preparation parameters. The resulting structural and magnetic properties were investigated using a range of experimental techniques confirming epitaxial growth of ${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ with the nominal stoichiometric composition and long-range magnetic order at and above room temperature. The main preparation parameter influencing the temperature ${T}_{f}$ of the bifurcation between $M(T)$ curves under field-cooled and zero-field-cooled conditions was found to be the growth rate of the films, while growth temperature or the Ar:${\mathrm{O}}_{2}$ ratio did not systematically influence ${T}_{f}$. Furthermore ${T}_{f}$ was found to be systematically higher for ${\mathrm{MgAl}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ as substrate and ${T}_{f}$ extends to above room temperature. While in some samples ${T}_{f}$ seems to be more likely correlated with superparamagnetism, the highest ${T}_{f}$ occurs in ${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ epitaxial films where experimental signatures of magnetic glassiness can be found. Element-selective x-ray magnetic circular dichroism measurements aim at associating the magnetic glassiness with the occurrence of a different valence state and lattice site incorporation of Fe pointing to a complex interplay of various competing magnetic interactions in ${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$.

Evolution of Compensated Magnetism and Spin-Torque Switching in Ferrimagnetic Fe1−xTbx

Compensated ferrimagnets (FIMs) made of rare-earth transition-metal compounds have stimulated increasing interest for enabling fast spin dynamics. Taking $\mathrm{Fe}$-$\mathrm{Tb}$ compounds as an example, substantial efforts have been made on the study of compensated magnetism and its potential spintronic applications. Current-induced spin-orbit torque (SOT) switching and its evolution with compensated ferrimagnetism in these compounds, however, remain to be systematically explored, which motivates the present study. By combining magnetometry and anomalous Hall effect measurements, a compositional magnetization compensation point (${x}_{c}$ = 0.25) is determined for ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}$ films of a fixed thickness of 6.5 nm. The antiferromagnetic coupling between $\mathrm{Fe}$ and $\mathrm{Tb}$ sublattices is directly revealed by conducting element-specific x-ray magnetic circular dichroism measurements. The evolution of SOT switching as a function of $\mathrm{Tb}$ concentration (x) in $\mathrm{Pt}/{\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}/\mathrm{Ta}$ multilayers is subsequently investigated. An enhanced SOT efficiency (approximately 3 times) is obtained at ${x}_{c}$ = 0.25. By conducting an endurance test, reliable SOT switching is revealed for over ${10}^{4}$ cycles. Our work suggests that compensated FIMs of composition ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}$ could be implemented for realizing efficient and stable spin-orbitronic performances.

Magnetic phase diagram mapping in Fe1−xRhx composition-spread thin films

We have fabricated high-quality polycrystalline Fe1−xRhx composition-spread thin films by cosputtering Fe and Rh, and investigated their structural and magnetic transformations as a systematic function of composition. With increasing Rh concentration, Fe1−xRhx thin film undergoes from an α׳ phase to a disordered γ phase and also shows a magnetic transition from a ferromagnetic phase to a paramagnetic phase. Vibrating-sample magnetometry and x-ray magnetic circular dichroism measurements show an antiferromagnetic-ferromagnetic transition in the range of 0.52 < x < 0.58 in the Fe1−xRhx composition gradient at room temperature. Based on our structural and magnetic property mapping, we construct a thin-film phase diagram of Fe1-xRhx. Compared to reported results in bulk alloys, the antiferromagnetic-ferromagnetic transition in the Fe1−xRhx thin films was found to occur at slightly higher Rh concentrations, while the boundary between the pure γ phase and the α׳/γ mixed phase region is shifted to the lower concentration Rh.

Ferrimagnetic-ferromagnetic phase transition in Au-doped Mn4N epitaxial films confirmed by x-ray magnetic circular dichroism

The antiperovskite ferrimagnet Mn4N has perpendicular magnetic anisotropy and small spontaneous magnetization, both of which are favorable properties for current induced domain wall motion. Previously we have investigated the magnetic structure of 3d-element-doped Mn4N thin films and demonstrated ultrafast domain wall velocities reaching 3000 m s−1 in the vicinity of the magnetic compensation composition of Ni-doped Mn4N at the current density of j = 1.2 × 1012 A m−2 at room temperature (RT). In this study, we investigate the effect of Au doping on the magnetic structure of Mn4N films, and present a composition ratio-dependent sign reversal of the anomalous Hall effect at RT. X-ray magnetic circular dichroism measurement revealed that the magnetic moment of the face-centered Mn atoms of Mn4−xAuxN reversed between x = 0.1 and 0.2, and became parallel to that of the corner-site Mn atoms for x = 0.2 and 0.3. This result suggests that the ferrimagnetic-ferromagnetic phase transition occurred in Au-doped Mn4N epitaxial films as in the In-doped Mn4N epitaxial films.

Intrinsically strained hexagonal Sr0.6Ba0.4MnO3 oxygen partial pressure dependent texturing and weak ferromagnetic behavior

We have probed the effect of intrinsic strain on the structural and magnetic properties of magneto-electric hexagonal Sr0.6Ba0.4MnO3 (SBMO) thin film grown by pulsed laser deposition on LaAlO3 (110) substrate by varying oxygen partial pressure (OPP). While the grown films show hexagonal structure with varying OPP, transition from oriented to polycrystalline growth is observed with increase in OPP. Raman spectroscopy confirms the P63/mmc symmetry of grown films along with the indication of distortion of octahedral. Magnetization measurements reveal room temperature weak ferromagnetic behavior in the thin films, which is in contrast to antiferromagnetic nature of its bulk counterpart. X-ray magnetic circular dichroism measurement confirms weak ferromagnetic behavior with contribution from unquenched orbital magnetic moment.

Pressure-induced charge orders and their postulated coupling to magnetism in hexagonal multiferroic LuFe2O4

Hexagonal LuFe2O4 is a promising charge order (CO) driven multiferroic material with high charge and spin-ordering temperatures. The coexisting charge and spin orders on Fe3+/Fe2+ sites result in magnetoelectric behaviors, but the coupling mechanism between the charge and spin orders remains elusive. Here, by tuning external pressure, we reveal three charge-ordered phases with suggested correlation to magnetic orders in LuFe2O4: (i) a centrosymmetric incommensurate three-dimensional CO with ferrimagnetism, (ii) a non-centrosymmetric incommensurate quasi-two-dimensional CO with ferrimagnetism, and (iii) a centrosymmetric commensurate CO with antiferromagnetism. Experimental in situ single-crystal X-ray diffraction and X-ray magnetic circular dichroism measurements combined with density functional theory calculations suggest that the charge density redistribution caused by pressure-induced compression in the frustrated double-layer [Fe2O4] cluster is responsible for the correlated spin-charge phase transitions. The pressure-enhanced effective Coulomb interactions among Fe-Fe bonds drive the frustrated (1/3, 1/3) CO to a less frustrated (1/4, 1/4) CO, which induces the ferrimagnetic to antiferromagnetic transition. Our results not only elucidate the coupling mechanism among charge, spin, and lattice degrees of freedom in LuFe2O4, but also provide a new way to tune the spin-charge orders in a highly controlled manner.

Oxygen vacancies at the origin of pinned moments in oxide interfaces: The example of tetragonal CuO/SrTiO3

Obtaining an accurate theoretical description of the emergent phenomena in oxide heterostructures is a major challenge. Recently, intriguing paramagnetic spin and pinned orbital moments have been discovered by x-ray magnetic circular dichroism measurements at the Cu ${L}_{2,3}$ edge of a tetragonal $\mathrm{CuO}/{\mathrm{SrTiO}}_{3}$ heterostructure. Using first-principles calculations, we propose a scenario that explains both types of moments, based on the formation of oxygen vacancies in the ${\mathrm{TiO}}_{2}$ interface layer. We show the emergence of a paramagnetic two-dimensional electron gas hosted in the interface CuO layer. It is invisible at the Ti ${L}_{2,3}$ edge since the valence of the Ti atoms remains unchanged. Strong structural distortions breaking both the local and global fourfold rotation ${C}_{4}$ symmetries at the interface lead to the in-plane pinning of the Cu orbital moment close to the vacancy. Our results, and in particular the pinning of the orbital moment, may have implications for other systems, especially monoxide/dioxide interfaces with similar metal-oxygen bond length and weak spin-orbit coupling.

Appearance of Ferromagnetism in Pt(100) Ultrathin Films Originated from Quantum-well States

Ferromagnetism was observed in a Pt(100) ultrathin film deposited on a SrTiO3(100) substrate. The ferromagnetism, which appears in films with thicknesses of 2.2-4.4 nm, periodically changes with a period of approximately 1 nm (5-6 monolayers) depending on the film thickness. This is consistent with the period derived from the quantum-well states formed in the thin film. X-ray magnetic circular dichroism measurements show the evidence of appearance of intrinsic ferromagnetism in Pt(100) ultra-thin film. In addition, present results suggest a possibility that the orbital magnetic moment of pure Pt is much smaller than that of the Pt/ferromagnetic multilayer system. These results will provide a potential new mechanism for origin of the large magnetic anisotropy in Pt components.

X-ray Absorption Spectroscopy Study of Thickness Effects on the Structural and Magnetic Properties of Pr2-δNi1-xMn1+xO6-y Double Perovskite Thin Films.

In this work, we report a systematic study of the influence of film thickness on the structural and magnetic properties of epitaxial thin films of Pr2-δNi1-xMn1+xO6-y (PNMO) double perovskite grown on top of two different (001)-SrTiO3 and (001)-LaAlO3 substrates by RF magnetron sputtering. A strong dependence of the structural and magnetic properties on the film thickness is found. The ferromagnetic transition temperature (TC) and saturation magnetization (Ms) are found to decrease when reducing the film thickness. In our case, the thinnest films show a loss of ferromagnetism at the film-substrate interface. In addition, the electronic structure of some characteristic PNMO samples is deeply analyzed using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements and compared with theoretical simulations. Our results show that the oxidation states of Ni and Mn ions are stabilized as Ni2+ and Mn4+, thus the ferromagnetism is mainly due to Ni2+-O-Mn4+ superexchange interactions, even in samples with poor ferromagnetic properties. XMCD results also make evident large variations on the spin and orbital contributions to the magnetic moment as the film's thickness decreases.

Origin of enhanced interfacial perpendicular magnetic anisotropy in LiF-inserted Fe/MgO interface

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-magnetic-moment-anisotropy enhancement to the stronger electron localization and electron-electron correlation or the better interface quality with fewer defects.

Magnetic structure of 3d-element doped Mn4N films confirmed by X-ray magnetic circular dichroism – Conditions for magnetic compensation

We investigated the magnetic structure of Mn4N epitaxial films doped with 3d elements and discussed conditions under which magnetization compensation (MC) occurs in these films at room temperature. Three examples are discussed here: Co-doped Mn4N, Fe-doped Mn4N, and Cr-doped Mn4N epitaxial films grown on SrTiO3(001) substrates. Mn4N is a ferrimagnet with an antiperovskite structure composed of two sublattices with their magnetizations aligned antiparallel to each other: Mn atoms at corner sites, Mn(I) atoms; and Mn atoms at face-centered sites, Mn(II) atoms. In a previous study, X-ray magnetic circular dichroism (XMCD) measurements revealed that Co atoms preferentially replaced Mn(I) atoms with their magnetic moments aligned antiparallel to those of Mn(I) atoms, and that the MC occurred at two Co compositions in Mn4−xCoxN epitaxial films (x ≤ 1.3) at room temperature (RT). At x > 1.3, however, there was no MC composition at RT. In contrast, no such preferential occupations sites were observed for Fe in Mn4−yFeyN (y ≤ 1.2) or Cr in Mn4−zCrzN (z ≤ 1.5) epitaxial films, and the MC did not occur in these films at RT. As for Mn4−yFeyN epitaxial films, XMCD measurements indicated that Fe atoms substituted for not only Mn(I) but also Mn(II) atoms even when the Fe composition was small (y < 1). Similar results were obtained for Cr atoms in Mn4−zCrzN epitaxial films. On the basis of these results, we reached a conclusion that the difference in site selectivity has a strong impact on the presence or absence of the MC point in Mn4N.

Sunlight-induced tri-state spin memory in photovoltaic/ferromagnetic heterostructure

The advanced spintronic devices demand a new routine of manipulating spin states effectively with low power consumption, fast switching, and non-volatility. Here, a photovoltaic heterojunction structure of (Cu, Ta)/Co40Fe40B20/(Ta, Cu) on a p-n junction Si wafer is proposed. The saturation magnetizations (Ms) tunability under sunlight illumination is decreased by ∼5–8 %. The first principle calculations reveal that the insert Cu or Ta layer promoted the photoelectron transmission, leading to a larger Ms tunability. Moreover, the Ta layer also generates a barrier between the p-n junction and CoFeB to keep the photoelectrons in the CoFeB layer, creating a non-volatility and sunlight/electrical dual-regulated tri-state magnetization change. Element-resolved X-ray magnetic circular dichroism (XMCD) measurement is also performed to determine the diminished intrinsic magnetism and corresponding non-volatility during sunlight illumination. These fundings explore a new method of magnetic modulation further to expand the non-volatile, low-power sunlight-driven spintronics.

Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films

Epitaxially strained SrRuO3 films have been a model system for understanding the magnetic anisotropy in metallic oxides. In this paper, we investigate the anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties using high-quality epitaxially strained (compressive and tensile) SrRuO3 films grown by machine-learning-assisted molecular beam epitaxy. The element-specific magnetic properties and the hybridization between the Ru 4d and O 2p orbitals were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements. The magnetization curves for the Ru 4d and O 2p magnetic moments are identical, irrespective of the strain type, indicating the strong magnetic coupling between the Ru and O ions. The electronic structure and the orbital magnetic moment relative to the spin magnetic moment are isotropic despite the perpendicular and in-plane magnetic anisotropy in the compressive-strained and tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a negligibly small contribution to the magnetic anisotropy. This result contradicts Bruno model, where magnetic anisotropy arises from the difference in the orbital magnetic moment between the perpendicular and in-plane directions. Contributions of strain-induced electric quadrupole moments to the magnetic anisotropy are discussed, too.

Electronic structure and magnetic anisotropy transition in Mn3−xCoxGa Heusler films investigated with soft x-ray spectroscopy

Employing soft x-ray magnetic circular dichroism (XMCD) and soft x-ray absorption spectroscopy (XAS), we have investigated electronic structures and spin configurations of Co-substituted ${\mathrm{Mn}}_{3}\mathrm{Ga}$ (${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$) Heusler films, which are promising spintronic materials exhibiting perpendicular magnetic anisotropy (PMA). Co $2p$ XAS and XMCD measurements, combined with the charge-transfer multiplet analysis, show that the substituted Co ions in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ consist of mainly ferromagnetic metallic Co clusters and a small amount of divalent Co ions with disordered magnetic moments. Mn $2p$ XAS and XMCD measurements show that Mn ions at both the octahedral and tetrahedral sites in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ are nearly divalent with weak covalent-bonding nature, reflecting non-Jahn-Teller ions, and that the magnetic moments of Mn ions are polarized along the ordered magnetic moments of the substituted Co ions. Angle-dependent Co $2p$ XMCD data of ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ agree with the weak magnetic anisotropy transition from PMA to in-plane magnetic anisotropy (IMA) with increasing $x$. Spin and orbital magnetic moments of Co ions are estimated by using the sum-rule analysis, which reveal negligible Co-content and polar-angle dependencies of the Co orbital to spin magnetic moment ratio. This work reveals that the PMA-to-IMA magnetic transition in ${\mathrm{Mn}}_{3\ensuremath{-}x}{\mathrm{Co}}_{x}\mathrm{Ga}$ is determined mainly by ferromagnetic metallic Co clusters.

Spin canting of Ni/CoO/Fe films grown on curved MgO(0 0 1) substrate

Using element-resolved x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) measurements, we determined the spin orientations of Ni, CoO and Fe films in Ni/CoO/Fe films grown on a curved MgO(001) substrate. We find that the vicinal surface of MgO(001) substrate results in a spin canting towards out-of-plane direction in the Ni and CoO films as a result of the interfacial coupling. The Ni spin canting angle increases monotonically with the vicinal angle in the studied range of 0–17° and the CoO spin canting angle increases more rapidly towards saturation only at a few degrees of the vicinal angle. The uniaxial magnetic anisotropy induced in the Ni layer by the Ni/CoO interfacial coupling is quantitatively determined and is shown to increase monotonically with the vicinal angle. Our result provides a new pathway for tailoring the spin orientation by modifying the substrate surface symmetry in combining with the ferromagnetic/antiferromagnetic interfacial interaction in thin-film based spintronic devices.

X-ray spectroscopy for the magnetic study of the van der Waals ferromagnet CrSiTe3 in the few- and monolayer limit

The study of magnetic order in few- and monolayer van der Waals materials poses a challenge to the most commonly employed magnetic characterization techniques as they normally lack magnetic sensitivity and/or lateral resolution enabling their thickness-dependent probing. Here we demonstrate the usefulness of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements, carried out at the Cr and Te M 5 edges, for the study of the ferromagnetic semiconductor CrSiTe3 (CST) in the form of single- and few-layer flakes. By scanning the sample under the incident x-ray beam, a map of the exfoliated system was obtained, which reproduced the optical micrographs showing the detailed distribution and thicknesses of the flakes. In this way, XAS/XMCD was performed at selected sample areas, revealing the thickness-resolved spectroscopic and magnetic properties of the flakes, such as the spin and orbital magnetic moments. The spin moment, in line with the saturation field, is decreasing with film thickness, revealing a single-domain and out-of-plane magnetization for the thinnest films. For CST, the electronic properties are governed by the strong covalent bond between the Cr 3d(e g ) and Te 5p states, giving rise to a superexchange scenario. We observed a gradually increasing ratio of orbital to spin moment for thinner flakes, which could be due to a further increase of the covalent mixing. Hysteresis loops were recorded at the Cr L 3 edge, showing an open loop for 10 down to ∼3 layers, while the bulk shows a wasp-waist shaped loop. With the transition temperature from the soft to the hard ferromagnetic state decreasing with thickness, the monolayer shows a narrowed, closed loop at 10 K, suggesting its transition temperature 10 K. Our study demonstrates the unique capabilities of XAS/XMCD for the study of few-layer van der Waals magnets, highlighting the interplay between electron correlation and ferromagnetism in CST.

Magnetic properties of the (Mo2/3R1/3)2AlC (R=Ho,Dy) i−MAX phases studied by x-ray magnetic circular dichroism and neutron diffraction

We report on the magnetic properties of single crystals of Ho- and Dy-based ${({\mathrm{Mo}}_{2/3}{R}_{1/3})}_{2}\mathrm{AlC} i\text{\ensuremath{-}}\mathrm{MAX}$ phases. In these nanolamellar compounds, where planes of $R$ and Mo arranged in a skewed triangular lattice are separated by planes of Al and C, geometrical frustration and magnetic exchange interactions lead to complex magnetic properties. Temperature-dependent bulk magnetization, specific heat, and resistivity measurements reveal two magnetic phase transitions in Dy $i\text{\ensuremath{-}}\mathrm{MAX}$ (15 and 12 K) and only one in Ho $i\text{\ensuremath{-}}\mathrm{MAX}$ (8.5 K). Strong magnetic anisotropy and metamagnetic transitions with a step at $\frac{1}{3}$ of saturation moment along the crystal $a$ axis are observed in field-dependent bulk magnetization curves. X-ray magnetic circular dichroism measurements unveil induced moments on Mo and Al, and a quantitative estimation of the orbital and spin moments of Mo based on magneto-optical sum rules suggests an unusual interaction between the $R 4f$ and the Mo $4d$ magnetic moments. Magnetic structures are derived from neutron diffraction measurements, revealing a zero-field incommensurate amplitude modulated order in both compounds, followed by an antiferromagnetic equal-moments structure at lower temperature for Dy $i\text{\ensuremath{-}}\mathrm{MAX}$. The bulk magnetization $\frac{1}{3}$ step is found to be linked to the flip of one $R$ moment out of three within the planes. Detailed phase diagrams for Ho and Dy $i\text{\ensuremath{-}}\mathrm{MAX}$ are derived from these measurements.

Study on FeCr thin film for a spintronic material with negative spin polarization

Negative spin polarization materials generate a spin current whose spin direction is opposite to the magnetization direction. This characteristic is technologically important because it increases the freedom in the design of spintronic devices. In this paper, we studied FeCr from the viewpoints of band structure, atomic magnetic moments, and local atomic arrangement to explore its potentiality as a negative spin polarization material. First-principles calculations on the disordered FeCr alloy predicted a high negative spin polarization, which was attributed to the band matching of the minority spin. We experimentally fabricated Fe1-xCrx thin films in the Cr concentration (x) range from 0.2 to 0.4 by sputter deposition and demonstrated inverse magnetoresistance using current-perpendicular-to-plane giant magnetoresistance (GMR) devices, which provided evidence of negative spin polarization. The spin polarization of Fe0.7Cr0.3 estimated from the GMR device measurements was −0.28 and fell below the calculated value. Synchrotron X-ray magnetic circular dichroism measurements showed a ferrimagnetic configuration of the Fe and Cr magnetic moments. The Fe moment showed a large moment over a wide Cr concentration range, whereas the Cr moment decreased with the Cr concentration, which agreed with the calculation result. Synchrotron Mössbauer spectroscopy measurements indicated the inhomogeneity of the FeCr composition even in the as-deposited state. Fe-rich regions were formed after annealing, reflecting the phase separation nature of the Fe-Cr system. Inhomogeneity was not considered in the calculation and could be the origin of the smaller negative spin polarization observed in the experiment.