Magnetic transitions induced by pressure and magnetic field in a two-orbital $5f$-electron model in cubic and tetragonal lattices

TL;DR

This study explores how pressure and magnetic fields influence magnetic phase transitions in a two-orbital 5f-electron model on cubic and tetragonal lattices, revealing that magnetic field favors the AF2 phase and pressure induces phase changes.

Contribution

It introduces a detailed analysis of pressure and magnetic field effects on Nél states in a two-orbital 5f-electron model, highlighting the conditions favoring different magnetic phases.

Findings

Magnetic field suppresses the AF1 phase and promotes the AF2 phase.

Pressure increases lead to transitions from AF1 to AF2 phases.

Tetragonal lattice favors AF2 phase more when magnetic field and c/a ratio increase.

Abstract

We investigate the onset and evolution of under the simultaneous application of pressure and magnetic field of distinct itinerant N\'eel 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 N\'eel order parameters $\phi^{\beta}$ and $\phi^{\alpha}$ are assumed to be fixed by an Ising anisotropy. The applied magnetic field $h_z$ 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 a important general result, we found that the magnetic field $h_z$ 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.