Magnetic Phase Transitions in Mn_3MC (M = Zn, Ga) and Orbital Magnetic Moments

(i)同步辐射实验研究为了研究Mn_3ZnC和Mn_3GaC钙钛矿磁相变的电子态，我们利用SPring-8 BL 39 XU开发的螺旋度调制技术进行了X射线磁圆二色性（XMCD）实验。在研究中，我们注意到Mn，Zn和Ga的K边，它们可以灵敏地反映相变引起的电子态的一些变化。特别是，已经系统地记录了XMCD对温度和磁场的依赖性。观察到Mn_3ZnC和Mn_3GaC中Mn K边XMCD随温度的急剧变化，并分别用二级和一级跃迁进行了讨论。我们的结论是，所观察到的行为是密切相关的相变引起的结构畸变，和轨道磁矩与磁结构转变。(ii)仪的研制 ...更多信息 高压下的实验对于高压低温条件下的XMCD实验，我们设计了一套将金刚石压砧和制冷机结合起来的装置，并将其安装在BL 39 XU上。该装置通过各种测试进行了改进，例如，冷却温度、高压运行、稳定性和振动。我们成功地在高压下对Fe_4N、Fe和Ni的K边进行了室温下的XMCD测量。同时，我们还对DyCo_2中Co K边的低温高压实验进行了研究。(iii)高压下Mn_3GaC中Ga的K边XMCD在300 K下成功地观察到了大于5GPa的In Mn_3GaC中Ga的K边XMCD，这表明在300 K下虽然是顺磁性的，但由于压力的作用，Ga的K边XMCD是铁磁性的。这首次给出了Ga原子磁极化的证据。系统的研究是非常必要的。(iv)研究成果的展示在2001年7月26日至31日在赤穗举行的第11届X射线吸收精细结构国际会议（XAFS-XI）上，我们以受邀演讲和海报展示的形式展示了研究成果。该海报被选为6个最佳海报奖之一。高压下Fe_4N中的XMCD方法研究成果发表在《核仪器》杂志上。方法.少

(i) Experimental Researches using Synchrotron RadiationTo study electronic states on magnetic phase transitions in Mn_3ZnC and Mn_3GaC perovskites, we have carried out X-ray magnetic circular dichroism (XMCD) experiment using the helicity-modulation technique developed at SPring-8 BL39XU. In the research, we paid our attention to Mn, Zn and Ga K-edges, which could sensitively reflect some modification in electronic states resulting from the phase transitions. In particular, dependences of XMCD on temperature and magnetic field have been systematically recorded. As a result drastic change in Mn K-edge XMCD in Mn_3ZnC and Mn_3GaC with temperature has been observed and discussed in terms of second-order and first-order transition, respectively. We have concluded that the observed behaviors are closely related to structural distortion induced by the phase transitions, and that orbital magnetic moments are associated with the magnetic structural transition.(ii) Development of Apparatus for … More the Experiments under High PressureFor the XMCD experiments under the conditions of high pressure and low temperature, we designed an apparatus combined a diamond-anvil cell with a refrigerator and installed it on BL39XU. This apparatus was improved through the various tests, e.g., cooling temperature, operation for high pressure, stability, and vibration. We succeeded in XMCD measurement under high pressure at K-edge in Fe_4N, Fe, and Ni at room temperature. And, we aimed for the experiment under high pressure at low temperature of Co K-edge in DyCo_2.(iii) Ga K-Edge XMCD in Mn_3GaC under High PressureIn Mn_3GaC Ga K-edge XMCD above 5 GPa has been successfully observed at 300K, which shows that ferromagnetic state is induced by the applied pressure, even though paramagnetism at 300K. This gives for the first time an evidence of Ga atom magnetically polarized. The systematic study is highly desired.(iv) Presentations of Research ResultsIn the 11-th International Conference on X-ray absorption fine structure (XAFS-XI), which was held at Ako, July 26-31 2001, we presented the results as an invited talk and a poster presentation. The poster was selected as one of the 6 best-poster awards. For the XMCD in Fe_4N under high pressure, methodological achievement was published to the journal of Nucl. Instrum. Methods. Less