Keisuke Ikeda

Electronic structure and magnetic properties of magnetically dead layers in epitaxial CoFe2O4/Al2O3/Si(111) films studied by x-ray magnetic circular dichroism

Epitaxial CoFe2O4/Al2O3 bilayers are expected to be highly efficient spin injectors into Si owing to the spin filter effect of CoFe2O4. To exploit the full potential of this system, understanding the microscopic origin of magnetically dead layers at the CoFe2O4/Al2O3 interface is necessary. In this paper, we study the crystallographic and electronic structures and the magnetic properties of CoFe2O4(111) layers with various thicknesses (thickness d = 1.4, 2.3, 4, and 11 nm) in the epitaxial CoFe2O4(111)/Al2O3(111)/Si(111) structures using soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) combined with cluster-model calculation. The magnetization of CoFe2O4 measured by XMCD gradually decreases with decreasing thickness d and finally a magnetically dead layer is clearly detected at d = 1.4 nm. The magnetically dead layer has frustration of magnetic interactions which is revealed from comparison between the magnetizations at 300 and 6 K. From analysis using configuration-interaction cluster-model calculation, the decrease of d leads to a decrease in the inverse-to-normal spinel structure ratio and also a decrease in the average valence of Fe at the octahedral sites. These results strongly indicate that the magnetically dead layer at the CoFe2O4/Al2O3 interface originates from various complex networks of superexchange interactions through the change in the crystallographic and electronic structures. Furthermore, from comparison of the magnetic properties between d = 1.4 and 2.3 nm, it is found that ferrimagnetic order of the magnetically dead layer at d = 1.4 nm is restored by the additional growth of the 0.9-nm-thick CoFe2O4 layer on it.

Anisotropic spin-density distribution and magnetic anisotropy of strained La 1−x Sr x MnO 3 thin films: angle-dependent x-ray magnetic circular dichroism

Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial strain from the substrate via strain-induced anisotropy in the orbital magnetic moment and that in the spatial distribution of spin-polarized electrons. However, the preferential orbital occupation in ferromagnetic metallic La1−xSrxMnO3 (LSMO) thin films studied by x-ray linear dichroism (XLD) has always been found out-of-plane for both tensile and compressive epitaxial strain and hence irrespective of the magnetic anisotropy. In order to resolve this mystery, we directly probed the preferential orbital occupation of spin-polarized electrons in LSMO thin films under strain by angle-dependent x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density distribution was found to be in-plane for the tensile strain and out-of-plane for the compressive strain, consistent with the observed magnetic anisotropy. The ubiquitous out-of-plane preferential orbital occupation seen by XLD is attributed to the occupation of both spin-up and spin-down out-of-plane orbitals in the surface magnetic dead layer.Magnetic anisotropy: spatial anisotropy of spin-polarized electrons probedEnabled by an angular dependent magneto-optical technique, the orbital states of spin-polarized electrons in La1-xSrxMnO3 thin films are directly probed. Goro Shibata from University of Tokyo and colleagues in Japan use an angular dependent x-ray magnetic circular dichroism (XMCD) technique to study the magnetic anisotropy of epitaxial La1−xSrxMnO3 (LSMO) thin films grown on SrTiO3 (STO) or LaAlO3 (LAO) substrate. The different substrates provide either tensile (STO) strain or compressive (LAO) strain. The strain modifies the orbital shapes of the spin-polarized electrons in LSMO layer, which can be directly probed by XMCD. The results show that the LSMO thin film under tensile (compressive) strain has in-plane (out-of-plane) spin-density distribution, which can be attributed to the preferential occupation of out-of-plane spin states at the surface. This helps to understand the strain controlled magnetic anisotropy in related materials.

Electronic states and possible origin of the orbital-glass state in a nearly metallic spinel cobalt vanadate: An x-ray magnetic circular dichroism study

We have investigated the orbital states of the orbital-glassy (short-range orbital ordered) spinel vanadate Co

Effects of cobalt substitution in L10 -(Fe,Co)Pt thin films

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Magnetic anisotropy of L10-ordered FePt thin films studied by Fe and Pt L2,3-edges x-ray magnetic circular dichroism

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High Mobility sub-60nm Gate Length Germanium-On-Insulator Channel pMOSFETs with Metal Source/Drain and TaN MIPS Gate

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Gate dielectric formation and MIS interface characterization on Ge

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Photoinduced valence transition in gold complexes Cs2Au2X6 (X=Cl and Br) probed by x-ray photoemission spectroscopy

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Systematic study of the electronic structure and the magnetic properties of a few-nm-thick epitaxial (Ni1-xCox)Fe2O4 (x = 0 - 1) layers grown on Al2O3(111)/Si(111) using soft X-ray magnetic circular dichroism: effects of cation distribution.

using x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and subsequent configuration-interaction cluster-model calculation. From the sign of the XMCD spectra, it was found that the spin magnetic moment of the Co ion is aligned parallel to the applied magnetic field and that of the V ion anti-parallel to it, consistent with neutron scattering studies. It was revealed that the excess Co ions at the octahedral site take the trivalent low-spin state, and induce a random potential to the V sublattice. The orbital magnetic moment of the V ion is small although finite, suggesting that the ordered orbitals mainly consists of real-number orbitals.

Magnetization process of the insulating ferromagnetic semiconductor (Al,Fe)Sb

We have studied the effect of cobalt substitution in