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

UGe_2中铁磁性与超导性共存的现象引起了许多科学家的关注。在铁磁相中观察到的超磁性已与超导机制密切相关。本项目的目的是利用磁性康普顿散射技术在原子尺度上理解超磁性。我们在常压下对铁磁UGe_2进行了磁康普顿散射实验，在32 K的超磁转变温度范围内没有发现自旋矩的异常。结合文献中已有的磁化数据，我们成功地分离了自旋矩和轨道矩。在10 ~ 60 K温度范围内，轨道矩与自旋矩之比（L/S）几乎是恒定的，L/S=-0.2 ~ -2.3。然而，在磁康普顿散射的线形（磁康普顿剖面）中，我们发现了跨超磁跃迁的显著变化。为了解释磁性康普顿谱变化的原因，我们拟合了不同磁量子数(m)的U-5f轨道的原子谱。本文拟合的L/S预测值与上述实验值吻合较好，表明本文模型拟合的有效性。拟合结果表明，观测到的磁康普顿谱的变化是由m=1和m=2轨道态的权值变化引起的，表明与Ge p态的杂化有很强的波动。此外，我们还进行了1.0 GPa的高压测量。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.