Magnetic Anisotropy Of Fine Particles
...s called a magnetic anisotropy energy. Generally it has the same symmetry as the crystal structure of the particle material, and we call it a magnetocrystalline anisotropy or crystal anisotropy . This kind of anisotropy is due mainly to spin-orbit coupling . For instance, we consider an anisotropy that is uniaxial in symmetry. In this case, one of the simplest expressions of the magnetic anisotropy energy is Ea=KaVsin2 , where is the angle between the magnetization vector and the symmetry axis of the particle, V is the volume of the particle, and Ka is the anisotropy energy per unit volume or the anisotropy constant. The srength of the anisotropy in any particular crystal is measured by the magnitude of the anisotropy constants. Consider a specimen of fine particles having no preferred orientation of its particles. If we have spherical particles, there will be no shape anisotropy, and the same applied field will magnetize it to the same extent in any direction. But if it is a nonspherical particles, the magnetization vector will not necessarily lie along an easy crystallographic axis, but rather along an axis whose demagnetizating field is...