Metamagnetism and thermodynamical properties in modulated systems: modelisation and application to PrNi 2Si 2

Abstract

A periodic field model taking into account explicitly the crystal field anisotropy is presented, in order to describe the thermodynamical properties and the magnetization process of incommensurate modulated magnetic systems. An application is made to the tetragonal PrNi 2Si 2 compound, where the crystal field and exchange parameters have been unambiguously determined, from a careful joint analysis of specific heat, magnetization, magnetic susceptibility and inelastic neutron scattering experiments. The ground state is a nonmagnetic singlet well isolated from another singlet and a magnetic doublet as the first two excited states. The existence of an amplitude modulated magnetic structure persisting from T N = 20 K down to 0 K is then well explained. It is shown that the periodic field model does not require any additional parameter to account quantitatively very well for the observed properties in the modulated ordered phase, in particular the variation of the specific heat and the metamagnetic process along the [001] easy magnetization direction.