Magnetic Phase Transitions fo Rare Earth Compounds Studied by the de Haas-van Alphen Effect

de Haas-van Alphen（dHvA）效应是确定费米面、回旋质量和传导电子散射寿命的最有效方法，我们生长了高纯度的稀土化合物单晶，并利用dHvA效应研究了稀土化合物的磁相变。我们发现了三种相变。实验结果如下：（1）反铁磁化合物的变磁转变我们研究了反铁磁化合物NdIn_3的dhvA效应。反铁磁态的费米面是由LaIn_3的费米面在大磁晶胞的基础上折叠成小布里渊区的能带过程构成的。(2)PrCu_2中基于四极矩的变磁相变我们发现，当磁场沿着正交结构的c轴方向时，PrCu_2中存在一种新的变磁相变。PrCu_2不是反铁磁化合物，而是Van-Vlec顺磁化合物，基态为4f能级。CeRu_2Si_2中4f电子的性质由巡游转变为定域CeRu_2Si_2在磁场沿着[001]方向作用时，在8 T下表现出变磁行为。我们详细地研究了在高达19 T的磁场和低于20 mK的温度下的dHvA实验，澄清了费米面。发现4f电子在性质上从巡游变为定域。

The de Haas-van Alphen (dHvA) effect is the most useful method to determine the Fermi surface, cyclotron mass and scattering lifetime of the conduction electron. We have grown high-purity single crystals and studied the magnetic phase transitions of the rare earth compound by the dhvA method. We have found three kinds of phase transitions. Experimental results are as follow ;(1) Metamagnetic transition in the antiferromagnetic compoundWe have studied the dhvA effect of the antiferromagnetic compound NdIn_3. The Fermi surface in the antiferromagnetic state is found to be constructed by the band folding procedure of the Fermi surface of LaIn_3 into the small Brillouin zone based on the large magnetic unit cell.(2) Metamagnetic transition based on the quadrupole moment in PrCu_2We have found a new type of metamagnetic transition in PrCu_2 when the field is directed along the c-axis of the orthorhombic structure. Here, PrCu_2 is not an antiferromagnetic compound but a Van-Vlec para-magnetic compound with the singlet ground state of the 4f level. This transition brings about the switching of the easy (a-axis) and hard (c-axis) axs in magnetization.Change of the 4f electron nature from itinerant to localized in CeRu_2Si_2The metamagnetic behavior is found at 8T in CeRu_2Si_2 when the field is directed along the [001] direction in the tetragonal structure. We have studied in detail the dHvA experiments in fields up to 19T and at temperatures down to 20mK and clarified the Fermi surface. the 4f-electron is found to be changed in nature from itinerant to localized.