ON THE RELATIONSHIP BETWEEN COERCIVE FORCE HC AND MAGNETIC VISCOSITY PARAMETER SV IN MAGNETIC-MATERIALS

Theoretical relationships between the coercive force Hc and the magnetic viscosity parameter Sv have been obtained which give a very good explanation to the well-known phenomenological Barbier plot. For the strong pinning model, the formula obtained is lgSv = lgHc - lg{( 75 4)[( 4fb 75 kT) 2 3 - 1]}, where f is maximum pinning force and b is the range of interaction between domain wall and pin. For the weak pinning model, the obtained theoretical formula is: lgSv = lgHc - lg{25[( 3 1rb2 25kT) - 1]}, where r is domain wall energy. For the unpinning (nucleation) process, the obtained formula is: lgSv = lgHc - lg{( 75 2)[( 4fb 75kT) - 1] 2 3}. For uniaxial single-domain particles, the obt ained relationship between Hc and Sv is: lgSv = lgHc - lg[( 2KV 1 2p kT)(V 1 2 - V 1 2p)], where Vp is the critical volume for superparamagnetic behaviour and V is the particle volume. At a given temperature, all the relationships obtained above can be written as: lgSv = const. + lgHc. © 1990.