Metastable fcc Fe-Rh Alloys and the Fe-Rh Phase Diagram

Single-phase metastable fcc Fe-Rh alloys have been obtained by rapid quenching from the liquid state over a wider range of compositions than formerly reported. Lattice spacings and Mössbauer spectra of Fe57 of these alloys have been measured at room temperature. Both lattice parameters and isomer shifts are found to vary smoothly with rhodium concentration. These experimental findings suggest the existence of a continuous gamma field at high temperatures. A tentative phase diagram based on the results of the present investigation is proposed

Electronic structure investigation of GdNi using X-ray absorption, magnetic circular dichroism and hard x-ray photoemission spectroscopy

GdNi is a ferrimagnetic material with a Curie temperature Tc = 69 K which exhibits a large magnetocaloric effect, making it useful for magnetic refrigerator applications. We investigate the electronic structure of GdNi by carrying out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at T = 25 K in the ferrimagnetic phase. We analyze the Gd M$_{4,5}$-edge ($3d$ - $4f$) and Ni L$_{2,3}$-edge ($2p$ - $3d$) spectra using atomic multiplet and cluster model calculations, respectively. The atomic multiplet calculation for Gd M$_{4,5}$-edge XAS indicates that Gd is trivalent in GdNi, consistent with localized $4f$ states. On the other hand, a model cluster calculation for Ni L$_{2,3}$-edge XAS shows that Ni is effectively divalent in GdNi and strongly hybridized with nearest neighbour Gd states, resulting in a $d$-electron count of 8.57. The Gd M$_{4,5}$-edge XMCD spectrum is consistent with a ground state configuration of S = 7/2 and L=0. The Ni L$_{2,3}$-edge XMCD results indicate that the antiferromagnetically aligned Ni moments exhibit a small but finite magnetic moment ( $m_{tot}$ $\sim$ 0.12 $\mu_B$ ) with the ratio $m_{o}/m_{s}$ $\sim$ 0.11. Valence band hard x-ray photoemission spectroscopy shows Ni $3d$ features at the Fermi level, confirming a partially filled $3d$ band, while the Gd $4f$ states are at high binding energies away from the Fermi level. The results indicate that the Ni $3d$ band is not fully occupied and contradicts the charge-transfer model for rare-earth based alloys. The obtained electronic parameters indicate that GdNi is a strongly correlated charge transfer metal with the Ni on-site Coulomb energy being much larger than the effective charge-transfer energy between the Ni $3d$ and Gd $4f$ states.Comment: 9 pages, 6 figures, text and figures revise

Anisotropic superconductivity mediated by phonons in layered compounds with weak screening effect

Anisotropic pairing interactions mediated by phonons are examined in layer systems. It is shown that the screening effects become weaker when the layer spacing increases. Then the anisotropic components of the pairing interactions increase with the screening length since the momentum dependence changes. As a result, various types of anisotropic superconductivity occur depending on the parameter region. For example, p-wave superconductivity occurs when the short-range part of Coulomb repulsion is strong and the layer spacing is large. Two kinds of inter-layer pairing may occur when the layer spacing is not too large. Although the phonon contribution to the d-wave pairing interaction is weaker than the p-wave interaction, it increases with the layer spacing. Relevance of the present results to organic superconductors, high-T_c cuprates, and Sr_2RuO_4 is discussed.Comment: 8 pages, 5 figures, (Latex, revtex.sty, epsf.sty

CaCu3Ru4O12: a high-kondo-temperature transition-metal oxide

遷移金属酸化物の近藤効果を初めて実証 --電子相関物性の設計・探索の新たなプラットホームを開拓--. 京都大学プレスリリース. 2022-01-31.Open access publication funded by the Max Planck Society.We present a comprehensive study of CaCu₃Ru₄O₁₂ using bulk sensitive hard and soft x-ray spectroscopy combined with local-density approximation + dynamical mean-field theory (DMFT) calculations. Correlation effects on both the Cu and Ru ions can be observed. From the Cu 2p core-level spectra, we deduce the presence of magnetic Cu²⁺ ions hybridized with a reservoir of itinerant electrons. The strong photon energy dependence of the valence band allows us to disentangle the Ru, Cu, and O contributions and, thus, to optimize the DMFT calculations. The calculated spin and charge susceptibilities show that the transition metal oxide CaCu₃Ru₄O₁₂ must be classified as a Kondo system and that the Kondo temperature is in the range of 500–1000 K

Electronic structure investigation of GdNi using x-ray absorption, magnetic circular dichroism, and hard x-ray photoemission spectroscopy

GdNi is a ferrimagnetic material with a Curie temperature TC=69 K which exhibits a large magnetocaloric effect, making it useful for magnetic refrigerator applications. We investigate the electronic structure of GdNi by carrying out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at T=25 K in the ferrimagnetic phase. We analyze the Gd M4,5-edge (3d-4f) and Ni L2,3-edge (2p-3d) spectra using atomic multiplet and cluster model calculations, respectively. The atomic multiplet calculation for Gd M4,5-edge XAS indicates that Gd is trivalent in GdNi, consistent with localized 4f states. On the other hand, a model cluster calculation for Ni L2,3-edge XAS shows that Ni is effectively divalent in GdNi and strongly hybridized with nearest-neighbor Gd states, resulting in a d-electron count of 8.57. The Gd M4,5-edge XMCD spectrum is consistent with a ground-state configuration of S=7/2 and L=0. The Ni L2,3-edge XMCD results indicate that the antiferromagnetically aligned Ni moments exhibit a small but finite total magnetic moment (mtot∼0.12μB) with the ratio mo/ms∼0.11. Valence band hard x-ray photoemission spectroscopy shows Ni 3d features at the Fermi level, confirming a partially filled 3d band, while the Gd 4f states are at high binding energies away from the Fermi level. The results indicate that the Ni 3d band is not fully occupied and contradicts the charge-transfer model for rare-earth based alloys. The obtained electronic parameters indicate that GdNi is a strongly correlated charge-transfer metal with the Ni on-site Coulomb energy being much larger than the effective charge-transfer energy between the Ni 3d and Gd 4f states

Erratum: Significantly enhanced giant Rashba splitting in a thin film of binary alloy (New Journal of Physics (2015) 083015)

10.1088/1367-2630/17/9/099502New Journal of Physics1799950

Significantly enhanced giant Rashba splitting in a thin film of binary alloy

10.1088/1367-2630/17/8/083015New Journal of Physics1788301

Polarization dependent hard X-ray photoemission experiments for solids: Efficiency and limits for unraveling the orbital character of the valence band

We have investigated the efficiency and limits of polarization dependent hard X-ray photoelectron spectroscopy (HAXPES) in order to establish how well this method can be used to unravel quantitatively the contributions of the orbitals forming the valence band of solids. By rotating the energy analyzer rather than the polarization vector of the light using a phase retarder, we obtained the advantage that the full polarization of the light is available for the investigation. Using NiO, ZnO, and Cu2O as examples for solid state materials, we established that the polarization dependence is much larger than in photoemission experiments utilizing ultra-violet or soft X-ray light. Yet we also have discovered that the polarization dependence is less than complete on the basis of atomic calculations, strongly suggesting that the trajectories of the outgoing electrons are affected by appreciable side-scattering processes even at these high kinetic energies. We have found in our experiment that these can be effectively described as a directional spread of +/- 18 degrees of the photoelectrons. This knowledge allows us to identify, for example, reliably the Ni 3d spectral weight of the NiO valence band and at the same time to demonstrate the importance of the Ni 4s for the chemical stability of the compound. (C) 2014 Elsevier B.V. All rights reserved