Metamagnetism of Cerium Compounds

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Some of the heavy electron compounds show a metamagnetic behavior. In heavy electron states magnetic moments of f-electrons are quenched. We expect that the process where the quenched magnetic moments revive as the external field is increased leads to the metamagnetism. The purpose of the present project is to study this phenomena in cerium compounds both from experimental and theoretical points of view.Experimentally we have studied the metamagnetism by magnetization, magnetoresistance, and de Haas van Alphen effect. We have succeeded to make good single crystals of CeCu_2. One of the characteristic features of the metamagnetism of this material is that the metamagnetic behavior occurs when the magnetic field is applied along the easy axis at around 20 kOe. The metamagnetic behavior is also observed as a sharp drop in the magnetoresistance. Fermi surfaces of antiferromagnetic Kondo materials, CeB_6, CeCu_2, CeIn_3 are determined by the dHvA experiments. Except for the folding effects … More in the antiferromagnetic phase, the Fermi surfaces do not change at the metamagnetic transition.From theoretical point of view a key question is how the magnetic moments are quenched in the heavy electron state. The fact that the metamagnetism occurs in the field in the easy axis, as observed in CeCu_2, supports the idea that the metamagnetism originates from a many body quenching of the magnetic moments rather than a crystalline field effect (spin flip process). To address the question, we have studied the one-dimensional periodic Anderson model and the one-dimensional Kondo lattice by the exact numerical diagonalization. Here we summarize the results for the Kondo lattice. Nature of the ground state changes as a function of density of conduction electrons : it changes from a ferromagnetic state at low density to a singlet with strong antiferromagnetic correlations at the half-filling. It has become clear that main mechanism which quenches the f-spins is mutual antiferromagnetic correlations rather that the Kondo screening. Less