Magnetic Anisotropy Of Fine Particles :: essays research papers

"Magnetic Anisotropy Of pretty Particles" In nature, single domain specks are magnetized to saturation, where the magnetization has an slowly axis, or several unaffixed axes, on which it prefers to lie. In this case the conglomeration internal life force is minimum. Rotation of the magnetization vector away from the easy axis is possible only by applying an external magnetised field. This phenomenon is called magnetic anisotropy. Thus, the term magnetic anisotropy describe the dependence of the internal energy on the direction of magnetization of the particle. The energy term of this kind is 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 primarily to spin-orbit coupling . For instance, we consider an anisotropy that is uniaxial in symmetry. In this case, one of the simplest expressions of th e 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 every 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 planetary particles, there will be no shape anisotropy, and the same utilise field will magnetize it to the same extent in whatever direction. But if it is a nonspherical particles, the magnetization vector will non necessarily lie along an easy crystallographic axis, but rather along an axis whose demagnetizating field is a minimum. This is called shape anisotropy and was proposed by (1947).In actually systems, there is always a particle size and shape distributions as well as a distribution of particle enviroments, depending on the network topology of the system (e.