Magnetic transitions induced by pressure and magnetic field in a two-orbital [formula omitted]-electron model in cubic and tetragonal lattices

Abstract

We investigate the onset and evolution of under the simultaneous application of pressure and magnetic field of distinct itinerant Néel states using the underscreened Anderson Lattice Model (UALM) which has been proposed to describe 5f-electron systems. The model is composed by two narrow f-bands (of either α or β character) that hybridize with a wide d-band and local 5f-electron interactions. We consider both cubic and tetragonal lattices. The Néel order parameters ϕβ and ϕα are assumed to be fixed by an Ising anisotropy. The applied magnetic field hz is parallel to the anisotropy axis. It has been assumed that the variation of the band width W is sensitive to pressure. In the absence of a magnetic field, the increase of W takes the system from the phase AF1 to another phase AF2. The phase AF1 occurs when ϕβ>ϕα>0 while in the AF2 phase the gaps satisfy ϕα>ϕβ>0. In the presence of a magnetic field hz, the phase AF2 is quickly suppressed and reappears again at intermediate values of the magnetic field while it is predominant at higher magnetic fields. The analysis of the partial density of states close to the phase transition between the phases AF1 and AF2, allows a better understanding the mechanism responsible whereby the transition is induced by an increase in the magnetic field. As an important general result, we found that the magnetic field hz favours the phase AF2 while the phase AF1 is suppressed. For the tetragonal lattice, the phase AF2 is even more favored when hz and c/a increases concomitantly, where c and a are the lattice parameters.