Meta-magnetism in Uranium-base Ferromagnetic Superconductors by Magnetic Compton Scattering

UGe_2的铁磁性与超导性共存现象引起了许多科学家的关注。在铁磁相中观察到的亚磁性与超导电性机制有关，已经得到了深入的研究。本项目的目的是利用磁康普顿散射技术在原子尺度上理解亚磁性，我们在常压下对铁磁UGe_2进行了磁康普顿散射实验，在亚磁性转变温度32 K范围内没有发现自旋磁矩的异常。结合已有的磁化强度数据，我们成功地分离了自旋和轨道矩。在10 ~ 60 K温度范围内，轨道矩与自旋矩之比（L/S）几乎为常数，L/S=-0.2 ~-2.3。然而，在磁康普顿散射的线形（磁康普顿轮廓）中，我们发现了在亚磁跃迁中的显著变化，为了解释磁康普顿轮廓变化的原因，我们拟合了不同磁量子数（m）的U-5 f轨道的原子轮廓。拟合结果表明，磁康普顿分布的变化是由m=1和m=2轨道态的权重变化引起的，说明与Ge p态的杂化有很强的涨落。我们在1.0 GPa下进行了高压测量。数据处理正在进行中。

Coexistence of ferromagnetism with superconductivity in UGe_2 has drawn much attention form many research scientists. The meta-magnetism observed in the ferromagnetic phase has been intensively studied in connection with the mechanism of the superconductivity. The aim of this project is to understand the meta-magnetism in an atomic-scale level by using the magnetic Compton scattering technique.We have carried out magnetic Compton scattering experiments on ferromagnetic UGe_2 at ambient pressure and have not find any anomalies in spin moment across the meta-magnetic transition temperature of 32 K. By combining with the magnetization data available in literatures, we have successfully separated the spin and orbital moments. The ratio of orbital moment to spin moment (L/S) is determined to be almost constanat, L/S=-0.2〜-2.3,over the temperature range between 10 K and 60 K. In the line-shape of magnetic Compton scattering (magnetic Compton profile), however, we have found significant changes across the meta-magnetic transition.In order to explain the origin of the changes observed in magnetic Compton profiles, we have fit atomic profiles of U-5f orbitals with different magnetic quantum number (m). The value of L/S predicted by the present fit is in good agreement with the above-mentioned, experimental values, showing the validity of the present model fitting.The fitting results show that the observed changes in the magnetic Compton profiles are caused by the changes of the weight of the m=1 and m=2 orbital states, suggesting strong fluctuation in the hybridization with Ge p states.In addition, we have performed high-pressure measurements at 1.0 GPa. The data-processing is in progress.