Magnetocrystalline anisotropy of Fe 3B, Fe 2B and Fe 1.4Co 0.6B as studied by Lorentz electron microscopy, singular point detection and magnetization measurements

Abstract

A magnetic domain study by means of Lorentz transmission electron microscopy has been carried out for the compounds Fe 3B, Fe 2B and Fe 1.4Co 0.6B. The magnetocrystalline anisotropy of these compounds has been derived from the Lorentz observations. Tetragonal Fe 3B has an in-plane anisotropy, with a preferential orientation along [110]. The orthorhombic modification of Fe 3B has the easy magnetization axis along the [100] direction. The magnetocrystalline anisotropy of Fe 2B and Fe 1.4Co 0.6B is found to be in-plane and uniaxial, respectively. The results for the latter two compounds are in agreement with those obtained from magnetic torque measurements, as reported in the literature. On the other hand, our results for tetragonal Fe 3B are different from those derived earlier by means of the Bitter technique. Anisotropy fields were obtained from Singular Point Detection experiments, and from magnetization curves. Implications of the results are discussed for the ratio between the remanence and saturation magnetization of Nd 4Fe 78B 18 permanent magnet alloys, containing tetragonal Fe 3B as the main phase.