STUDY OF STRONGLY CORRELATED SYSTEMS: HEAVY FERMIONS AND ITINERANT FERROMAGNETS

Abstract

This thesis is devoted to the study of electronic and magnetic properties of strongly correlated systems like transition metal & their compounds (d-electron itinerant ferromagnets) and rare-earth, actinides & their compounds (f-electron systems e.g. Heavy Fermions). In these systems the U/D ratio is very large, where U is the intra-site Coulomb repulsion and D is the width of the d-band or f-band. Heavy Fermion (HF) systems are the inter-metallic compounds containing rare-earth and actinides such as UBe13, UPt3, U2Zn17, CeCu2Si2, CeCu6, CeAl3, CeRu2Si2, YbA113, YbCuAl, YbCu2Si2, NpBe13, NpSn3, etc. exhibit interesting physical phenomenon, such as valence fluctuation, charge fluctuation, extremely high value of electron effective mass, very high electronic specific heat (large y), anomalous transport behavior, etc. Large value of y has been attributed to strongly correlated f-electrons of the rare-earth and actinides. It has been shown, experimentally, by many workers, that above a characteristic temperature T*, these systems show magnetic susceptibility explained by Curie-Weiss law and Pauli-like behavior of magnetic susceptibility at very low temperatures. In addition some HF systems show antiferromagnetic order and superconducting order at low temperatures. During last two decades it is well established that periodic Anderson model (PAM) can very well explain various properties of HF systems.