SPring-8 Seminar (第175回)
副題/演題 | Ferromagnetic Semiconductors with high Curie temperature and unusual magnetic properties - the case of Gd-doped GaN |
---|---|
開催期間 | 2008年02月06日 |
開催場所 | 上坪講堂 |
主催 | 財団法人高輝度光科学研究センター(JASRI) |
形式 | |
分野 | 物質科学 |
概要 |
日時: 2008年2月6日(水)15:00~ 場所: 上坪講堂 Speaker : Dr. Klaus H. Ploog Affiliate : Paul Drude Institute for Solid State Electronics Title : Ferromagnetic Semiconductors with high Curie temperature and unusual magnetic properties - the case of Gd-doped GaN Abstract : We have recently observed room-temperature ferromagnetism in Gd-doped semi-insulating GaN films grown on SiC(0001) by molecular beam epitaxy. In addition to the high Curie temperature of >800 K, our measurements have revealed an unexpectedly high magnetic moment per Gd atom and a magnetic anisotropy with the hard axis along the [0001] growth direction and an easy plane parallel to the GaN surface. The temperature dependence of the magnetic properties showed the existence of two ferromagnetic phases with different order temperature. The coexistence of two ferromagnetic phases can be explained within the framework of our phenomenological model which assumes a large polarization of the GaN matrix by the Gd atoms. We also found that the saturation magnetization shows a dependence on the orientation of the magnetic field, which may result from the anisotropy of the polarization induced in the GaN matrix by internal and external magnetic field. It is finally important to note that ferromagnetic GaN films with high Curie temperature can also be produced by Gd-focussed ion beam implantation into as-grown GaN. The observed magnetic moment per Gd atom became even higher in as-implanted samples, and the measured saturation magnetization of as-implanted GaN could be reduced by thermal annealing at 800 C. This finding points to the important role which defects may play as "mediators" in the exchange coupling between the Gd atoms. In addition to the Gd-doped GaN films described here, room-temperature ferromagnetism has also been observed in Co-doped ZnO and anatase TiO(2). In these rather disordered wide-gap semiconductors the standard indirect exchange mechanisms in the absence of free carriers are too short range to overcome the percolation threshold and establish a long-range magnetic order. Intrinsic or extrinsic defects may thus play the part of "mediators" in the inter-impurity exchange coupling. 担当者: 高橋正光(PHS 3866) |
問い合わせ先 |
JASRI 研究調整部 研究業務課 SPring-8セミナー事務局
垣口 伸二、濱中裕子 0791-58-0839 0791-58-0988 spring8_seminar@spring8.or.jp |