Magnetic state in iron hydride under pressure studied by X-ray magnetic circular dichroism at the Fe K-edge
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1262-W04-02
Magnetic state in iron hydride under pressure studied by X-ray magnetic circular dichroism at the Fe K-edge N. Ishimatsu1, Y. Matsushima1, H. Maruyama1, T. Tsumuraya2,*, T. Oguchi2, N. Kawamura3, M. Mizumaki3, T. Matsuoka3, and K. Takemura4 1
Gradate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 7398526, Japan 2 Gradate School of Advanced Science of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530, Japan 3 Japan Synchrotron Research Institute/SPring-8, 1-1-1, Kouto, Sayo, 679-5198, Japan 4 National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan *present address: Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208-3112, USA ABSTRACT In order to study magnetic states in Fe-hydride under pressure, X-ray magnetic circular dichroism (XMCD) at the Fe K-edge has been measured up to 27.5 GPa. As a result, hydrogenation from bcc-Fe to dhcp-FeH occurs within a narrow region of 3.2-3.8 GPa, which is clearly observed by the dichroic profile in dhcp-FeH differing from that in bcc-Fe. Influence of H atoms on Fe 3d and 4p electronic states is discussed using the pressure-dependent XMCD and the first-principles calculation. INTRODUCTION Metal hydrogen system has recently attracted scientific and technological interests because of its increasing demand for hydrogen storage materials. Insertion of hydrogen atoms leads to volume expansion of the host metal and/or structural transition, which results in the drastic changes in brittleness, electric resistivity, optical transparency, and so on [1]. In the case of 3d ferromagnetic transition metals, Fe, Co and Ni, hydrogenation also gives rise to some changes in their magnetic properties [2,3]. Influence of the hydrogenation on the electronic and magnetic structure has an important role for these phenomena. Hydrogen solubility of the 3d transition metals is significantly low at atmospheric pressures; however, the hydrogenation further proceeds under the order of GPa hydrogen pressures. In the case of iron, bcc-Fe is rapidly hydrogenated to ferromagnetic FeH in H2 fluid under pressure higher than 3.5 GPa.[4] FeH takes a double hcp (dhcp) structure (space group: P63mmc), in which Fe atoms occupy 2a and 2c sites whereas H atoms occupy 4f site [5]. It has been predicted that H atoms are slightly displaced towards Fe at 2a site from the center position [2,3]. Mössbauer spectroscopy has revealed two different hyperfine fields, indicating that Fe atoms carry different magnitude of magnetic moment [6]. These magnetic properties contrast with the non-magnetic state in hcp Fe observed under pressures higher than 14 GPa [7]. To study the magnetic property in FeH, it is crucial to understand the modification of the electronic structure due to the hydrogenation and stability of the ferromagnetism under pressure. For this purpose, X-ray magnetic circular dichroism (XMCD) is a powerful spectroscopic technique because it enables us to probe magnetically polarized electronic states wi
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