Research of High-Field Magnetization in Transuranium Neptunium Compounds

我们测量了NpRhGa_5和NpO_2以及相关化合物UO_2的高场磁化强度。在此基础上，推出了价格昂贵、难以购买的新型瞬态存储器设备Sigma 90，并开发了相应的测试系统。利用该测量系统可以获得高质量的磁化数据。通过测量高场磁化强度与温度的关系，得到了NpRhGa_5的磁相图。根据这一结果，在变磁一级相变时，约1 μ_B/Np的大磁矩（磁各向异性为[110]）转变为约0.5 μ_B/Np的小磁矩（无磁各向异性）。低温态的基态用Kiss和Kuramoto的四极相互作用理论表示。这意味着该系统可以用局域矩5 f电子模型来解释。另一方面，我们测量了5 f电子的de Haas-van Alphen振荡，结果表明5 f电子是巡游的。这些结果表明，该化合物的磁性不能用简单的定域或巡游f电子模型来解释。NpO_2的磁化强度在T_N以下始终呈线性。这一结果表明5 f电子之间的反铁磁相互作用非常强。这些成果在国际会议上得到了体现，如SCES 05（维也纳）、Handai论坛（河内）、ICM 2006（京都）和RHMF 2006（仙台）。这些结果也将在联合警察处会议上得到介绍。

We measured high-field magnetization in NpRhGa_5 and NpO_2 and related compound, UO_2. The New transient memory equipment 'Sigma90' was introduced, which was too expensive to buy with this foundation, and developed the related measurement systems by this foundation. Then high-quality magnetization data can be obtained with this new measurement system. The magnetic phase diagram of NpRhGa_5 is obtained by the measurement of the temperature dependence of the high-field magnetization. According to this results, the large magnetic moment of about 1 μ_B/Np with magnetic anisotropy of [110] changes to the small magnetic moment of about 0.5 μ_B/Np with no magnetic anisotropy at the metamagnetic first order transition. The ground state of low temperature state is represented by the theory of Kiss and Kuramoto with the quadrupolar interaction. This means that the system can be explained by the local moment 5f-electron model. On the other hand, the de Haas-van Alphen oscillations are measured and this results shows the 5f-electron is itinerant. These results shows that the magnetism of this compound cannot be explained by the simple localized or itinerant f-electron model. The magnetization of NpO_2 shows always linear below T_N.. This result shows the antiferromagnetic interaction between 5f-electrons is very strong. These results are represented in the international conferences, SCES05 (Vienna ), Handai forum (Hanoi), ICM2006 (Kyoto) and RHMF2006 (Sendai). These results also be represented in the JPS meetings.