Nucleation and pinning at 360° domain walls in SmCo5 and related alloys

It is shown that in a high forward field neighboring 180° ferromagnetic domain walls come together and either annihilate one another (’’unwinding walls’’) or combine to form 360° walls separating domains magnetized in the same direction (’’winding walls’’). If the 360° wall encounters:i an inhomogeneity of lower zero-field wall energy (∞𝒵AK), it may be pinned. A finite reverse field is then required to split the 360° wall nucleus into two transient 180 ° walls which will reverse the magnetization. The model is developed micromagnetically and applied to the pinning of domain walls at grain boundary inhomogeneities in SmCo5 alloys. The nucleation–unpinning coercive field is calculated for inhomogeneities which are assumed to have the magnetic properties of pure cobalt. Inhomogeneity widths from 55.6 to 204 Å give coercive forces from zero to 3.8×104 Oe..A critical constants chosen, this thickness is 55.6 Å It is suggested that one function of liquid-phase sintering may be to increase the inhomogeneity thickness beyond the critical value.