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

(I)利用同步辐射的实验研究为了研究Mn_3ZnC和Mn_3GaC钙钛矿中磁性相变的电子态，我们利用在Spring-8 BL39XU上发展的螺旋度调制技术进行了X射线磁性圆二色(XMCD)实验。在研究中，我们注意到了能灵敏地反映相变引起的电子态变化的Mn、Zn和Ga K边。特别是系统地记录了XMCD随温度和磁场的变化关系。观察到了Mn3ZnC和Mn3GaC中的MnK边XMCD随温度的急剧变化，并分别从二级相变和一级相变的角度进行了讨论。我们的结论是，观察到的行为与相变引起的结构扭曲密切相关，轨道磁矩与磁结构转变有关。(Ii)…装置的研制在高压低温条件下的XMCD实验中，我们设计了一种将金刚石压腔与电冰箱相结合的装置，并将其安装在BL39XU上。通过冷却温度、高压运行、稳定性和振动等多项试验，对该装置进行了改进。我们在室温下成功地测量了Fe_4N、Fe和Ni的K边高压XMCD。并针对DyCO_2中Co K边的低温高压实验进行了研究。(Iii)在300K下，在高压下观察到了Mn_3GaC中的Ga K边XMCD，高于5 GPaGa K边XMCD，这表明即使在300K下顺磁性的存在，也是由外加压力诱导的。这第一次给出了Ga原子磁极化的证据。在2001年7月26-31日在Ako举行的第11届X射线吸收精细结构国际会议(XAFS-XI)上，我们以应邀演讲和海报演示的形式介绍了研究结果。这张海报被选为6个最佳海报奖之一。对于高压下Fe_4N中的XMCD，方法学成果发表在《原子核》杂志上。Instrum。方法：研究方法。较少

(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