Phonon dispersions and structural transitions of CrO$_{2}$ under high pressure

Phonon dispersions of chromium dioxide (CrO$_{2}$) are calculated to investigate the structural phase transitions as a function of pressure. The structural phase transition has been confirmed from the ground state tetragonal CrO$_{2}$ of rutile-type (t-CrO$_{2}$) to the orthorhombic CrO$_{2}$ of CaCl$_{2}$-type (o-CrO$_{2}$). The ferromagnetic and half-metallic property is preserved even in o-CrO$_{2}$. The softening of Raman-active B$_{1g}$ phonon mode, which is relevant to the above structural transition, is also obtained. We will discuss the possible more structural phase transitions from o-CrO$_{2}$ and the related phonon and magnetic properties at much higher pressure.