de Haas-van Alphen Effect in the Heavy Fermion Compound with Amplitude-Modulated Magnetic Structure

(1)LaNi_2Al_5的德哈斯-范艾芬效应和费米面的研究：通过磁阻和德哈斯-范艾芬测量来研究LaNi_2AI_5的费米面性质，LaNi_2AI_5是磁致密近藤化合物CeNi_2AI_5的参考材料。在角分辨dHvA测量中观察到了频率从1.25x10^6到101x10^6 Oe的13个分支，并且磁阻显示了开放轨道的存在。 FLAPW能带结构计算得到的费米面很好地解释了这一结果。(2)磁致密近藤化合物CeNi_2AI_5的德哈斯-范阿尔芬效应和费米面研究：在低至40 mK的温度下，在具有不相称磁结构的CeNi_2AI_5中进行了德哈斯-范艾芬(dHvA)效应实验。磁转变场与温度的复杂相图已完成。在较高场区域 II、III 和 IV 中观察到的 dHvA 频率的许多分支，可以通过从非磁性参考样品 LaNi_2AI_5 的理论费米面预测的分支来更好地理解，而不是通过将 4f 电子视为流动的 CeNi_2AI_5 中的理论费米面来理解。最低场I区观察到的分支与LaNi_2AI_5或CeNi_2AI_5中的理论预测分析不清晰，在IV区观察到具有大回旋质量的电子； eta 分支为 12.4 m_0，zeta 分支为 11.2 m_0，theta 分支为 9.6 m_0。由于与磁性相关的自旋分裂，观察到一些对的平行分支，并获得交换能DELTA E； β 分支中的 DELTA E=12.9 meV，δ 分支中的 7.8 meV。讨论了费米面与磁结构之间的关系。

(1) Studies of de Haas-van Aiphen Effect and Fermi Surfaces of LaNi_2Al_5 :Magnetoresistance and de Haas-van Alphen measurements have been performed to investigate Fermi-surface property of LaNi_2AI_5, which is a reference material of a magnetic dense-Kondo compound CeNi_2AI_5. Thirteen branches with the frequencies from 1.25x10^6 to 101 x10^6 Oe have been observed in the angular-resolved dHvA measurements, and the magnetoresistance shows the existence of open orbits. The results are well explained by the Fermi surfaces obtainedfrom an FLAPW band-structure calculation.(2) Studies of de Haas-van Alphen Effect and Fermi Surfaces of Magnetic Dense-Kondo Compound CeNi_2AI_5 :The experiments of de Haas-van Aiphen (dHvA) effect have been carried out at temperatures down to 40 mK in CeNi_2AI_5 with an incommensurate magnetic structure. A complex phase diagram of the magnetic transition field versus temperature is completed. Many branches of the dHvA frequencies observed in the higher-field regions, II, Ill and IV, have been understood by the branches predicted from the theoretical Fermi surfaces of nonmagnetic reference-sample LaNi_2AI_5 better rather than the theoretical ones in CeNi_2AI_5 with 4f electrons treated as itinerant. Branches observed in the lowest field region I are not clearly analyzed with the theoretical prediction in LaNi_2AI_5 or CeNi_2AI_5, The electrons with heavy cyclotron mass are observed in the region IV ; 12.4 m_0 in eta branch, 11.2 m_0 in zeta branch and 9.6 m_0 in theta branch. Some pairs of parallel branches are observed due to the spin-splitting related to the magnetism, and the exchange energy DELTA E is obtained ; DELTA E=12.9 meV in beta branch and 7.8 meV in delta branch. The relations between the Fermi surfaces and the magnetic structure are discussed.