Spin reorientation in CoV2O4 thin film from first principles calculation

AV2O4 shows an interplay between spin, lattice and orbital degrees of freedom which manifests in the multiple structural and magnetic phase transitions. CoV2O4 (CVO) shows no or very weak cubic to tetragonal structural phase transition and two magnetic (paramagnetic to collinear ferrimagnetic (FM) and collinear to noncollinear FM) phase transitions at lower temperatures in its bulk form. In a recent experiment, an epitaxial thin film of CVO grown on the SrTiO3 (001) substrate, is observed to have an orthorhombic structural phase accompanied by a noncollinear magnetic state where the spin moments of Co and V are reoriented from (001) (seen in the bulk form) to the (110) direction. In this work, we have explored this complex noncollinear magnetic ground state by investigating the electronic, magnetic, and structural properties of CVO thin film using the first principles density functional theory. Our calculations show that the large exchange coupling strength in ab-plane as opposed to the c-direction in the orthorhombic phase can possibly explain the shifting of the FM easy axis to the (110) plane. Our calculated the ground state noncollinear magnetic structure shows a two-in-two-out form of V moments on each V4O4 cube, The possible orbital ordering has also been explored.