Magnetic Anisotropy, Magnetostriction, and Magnetic Domain Walls in NiO. I. Theory

Abstract

A general expression of the magnetic anisotropy energy and the magnetoelastic energy in the crystal of magnetic symmetry D 3 d is obtained. It is shown that, in NiO, the easy directions of magnetization will be either turnrightup.eps[1\bar10] or directions very close to turnrightup.eps[11\bar2] when the easy plane is (111), and that, in either case of easy directions, the spontaneous magnetostriction should consist of two strain components representing an orthorhombic deformation and a monoclinic deformation. The magnetoelastic energy is calculated taking four kinds of atomistic origin into account. Contributions from these origins to the energy are shown to be nearly of the same magnitude, and the magnetostrictive strain in NiO is estimated to be of the order of 10 -4 from the calculated energy values and the elastic constants of MgO. Possible directions of magnetic domain walls (S-walls) in such a crystal are predicted from the symmetry of the magnetostrictive strain.