Itinerant electrons and local moments in high and low magnetic fields: theoretical analysis of metamagnetism and paramagnetic susceptibility

Starting from a periodic Anderson Hamiltonian in the presence of an applied magnetic field, we present a model of the field-induced metamagnetism. Equations of motion for the magnetization and spin-fluctuation amplitudes are derived using Heisenberg's equation. A non-linear equation is set up, which connects the applied field (h) with magnetization (m). Spin fluctuation and magnetization dampings are considered phenomenologically. Metamagnetism is shown to be driven by the transverse part of the applied field and strong electron correlations are found to be important in the high field state. The low-field paramagnetic susceptibility is also analyzed for an itinerant electron system in the presence of conduction electron moment and localized moment (c-1) hybridization. In the process we derive an expression for the spin susceptibility of an itinerant electron system and express it as a sum of exchange enhanced Pauli spin susceptibility and a part which is written as a product of the electron paramagnetic resonance (EPR) shift and the Curie-Weiss susceptibility. The EPR shift is very much similar to the Knight shift, if a contact interaction for the c-1 hybridization is assumed. The agreement with experimental observation in CeRu2Si2 is good on qualitative grounds. (C) 2003 Elsevier B.V. All rights reserved.