Torque curve measurements in HCP Co in very low fields

Magnetic torque measurements have been made for a single crystal of Co of hcp structure in a very low field region where the torque intensity was not saturated. In this region it had been considered to be impossible to determine the magnetocrystalline anisotropy constants from observed torque curves. Recently, a new method of analyzing the torque curves was proposed by the present author with the help of a least mean square routine instead of the usual Fourier analysis. By using this method the first magnetocrystalline anisotropy constant Kulwas, for the first time, determined at 77 K. It was found that the Kuldetermined in the low field range between 0.3 and 0.5 T coincides with the value determined at a high field region where the torque curve was saturated enough. Below 0.2 T the value of Kuldecreased with decreasing the field. This region was found to correspond to the domain wall formation.