The availability of Henkel plots for sintered hard/soft magnetic composite ferrites

Henkel plots of several kinds of hard/soft magnetic composites with exchange coupling interaction, including SrFe₁₂O₁₉/(Ni,Zn)Fe₂O₄, SrFe₁₂O₁₉/CoFe₂O₄ and SrFe₁₂O₁₉/Fe–B, were obtained from the recoil loops in the initial magnetization and demagnetization state measured by a vibrating sample magnetometer. It is found that the magnetocrystalline anisotropy constant (K) and coercivity (H_c) of 'soft' phases could affect the availability of Henkel plots greatly. The Henkel plot could be used to characterize the existence and strength of exchange coupling interaction only in a composite with a 'soft' phase of small K and H_c, and it deviates markedly from the reality for a composite of a 'soft' phase of relatively large K and H_c.