First principles study of structural, magnetic and electronic properties of half-metallic CrO2 under pressure

A first-principles tight-binding linear muffin tin orbital (TB-LMTO) method within the local-density approximation is used to calculate the total energy, lattice parameter, bulk modulus, magnetic moment, density of states and energy band structures of half-metallic CrO2 at ambient as well as at high pressure. The magnetic and structural stabilities are determined from the total energy calculations. From the present study we predict a magnetic transition from ferromagnetic (FM) state to a non-magnetic (NM) state at 65 GPa, which is of second order in nature. We also observe from our calculations that CrO2 is more stable in tetragonal phase (rutile-type) at ambient conditions and undergoes a transition to an orthorhombic structure (CaCl2-type) at 9.6 GPa, which is in good agreement with the experimental results. We predict a second structural phase transition from CaCl2- to fluorite-type structure at 89.6 GPa with a volume collapse of 7.3%, which is yet to be confirmed experimentally. Interestingly, CrO2 shows half metallicity under ambient conditions. After the first structural phase transition from tetragonal to orthorhombic, half metallicity has been retained in CrO2 and it vanishes at a pressure of 41.6 GPa. Ferromagnetism is quenched at a pressure of 65 GPa.