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

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(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