Abstract

We investigate the onset and evolution of under the simultaneous application of pressure and magnetic field of distinct itinerant Neel 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 alpha or beta character) that hybridize with a wide d-band and local 5f-electron interactions. We consider both cubic and tetragonal lattices. The Neel order parameters Phi(beta) and Phi(alpha) 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 AF(1) to another phase AF(2). The phase AF(1) occurs when Phi(beta) > Phi(alpha) > 0 while in the AF(2) phase the gaps satisfy Phi(alpha) > Phi(beta) > 0. In the presence of a magnetic field h(z), the phase AF(2) 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 AF(1) and AF(2), 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 AF(2 )while the phase AF(1) is suppressed. For the tetragonal lattice, the phase AF(2) is even more favored when h(z )and c/a increases concomitantly, where c and a are the lattice parameters.