Pressure-induced Phonon Softenings and the Structural and Magnetic Transitions in CrO$_{2}$

TL;DR

This study investigates pressure-induced structural and magnetic transitions in CrO₂, revealing phonon softening and phase changes at specific pressures, including a newly identified transition at 88.8 GPa.

Contribution

It provides detailed insights into the pressure-driven structural and magnetic phase transitions of CrO₂, including phonon behavior and the discovery of a new high-pressure phase.

Findings

First transition at ~10 GPa from tetragonal to orthorhombic structure.

Preservation of half-metallicity in the orthorhombic phase.

Second transition at ≥61.1 GPa from ferromagnetic to nonmagnetic phase.

Abstract

To investigate the pressure-induced structural transitions of chromium dioxide (CrO$_{2}$), phonon dispersions and total energy band structures are calculated as a function of pressure. The first structural transition has been confirmed at P$\approx$ 10 GPa from the ground state tetragonal CrO$_{2}$ (t-CrO$_{2}$) of rutile type to orthorhombic CrO$_{2}$ (o-CrO$_{2}$) of CaCl$_{2}$ type. The half-metallic property is found to be preserved in o-CrO$_{2}$. The softening of Raman-active B$_{1g}$ phonon mode, which is responsible for this structural transition, is demonstrated. The second structural transition is found to occur for P$\geq$ 61.1 GPa from ferromagnetic (FM) o-CrO$_{2}$ to nonmagnetic (NM) monoclinic CrO$_{2}$ (m-CrO$_{2}$) of MoO$_{2}$ type, which is related to the softening mode at {\bf q} = R(1/2,0,1/2). The third structural transition has been newly identified at P= 88.8 GPa from m-CrO$_{2}$ to cubic CrO$_{2}$ of CaF$_{2}$ type that is a FM insulator.