Magnetization, Magnetocrystalline Anisotropy, Domain Wall Energies and Thicknesses in R₂Fe₁₄B Materials With R = Nd,Gd,Dy and Ho

Abstract

Measurements of magnetization and magnetocrystalline anisotropy have been made in three compounds (R = Gd,Dy and Ho) over a range of temperatures from 4.2 to 350K. Observations of domain structure have been made on these compounds and also on the corresponding Nd compound. From measurements on the basal plane domain patterns the domain wall energies and thicknesses have been calculated using the measured magnetization and anisotropy. Good agreement is found between values calculated in this way and values calculated using the basic magnetic parameters except in the case of Gd₂Fe₁₄B. It is suggested that the model used is inappropriate in this case owing to the weak anisotropy. Changes of domain structure in a Nd₁₅Fe₇₇B₈ ingot have been observed around part of the hysteresis cycle. Saturation can be achieved in grains with their c-axis parallel to the applied field at fields low compared to the coercivity. This indicates the importance of the correct processing of material with good intrinsic properties to enhance the coercivity.