Comparison of the zero-field-cooled magnetization behavior of some ferromagnetic and ferrimagnetic systems

The zero-field-cooled (ZFC) magnetization behavior of two ferromagnetic oxides, SrRuO3 and La2/3Ca1/3MnO3, and two ferrimagnetic oxides, MnCo2O4 and NiFe2O4, has been compared. It has been observed that a peak or maximum in M-ZFC(T) is obtained (at T-p less than or equal to T-c) in a given temperature range only when measured with magnetic fields less than a critical value, H-cr, which is temperature dependent. H-cr corresponds to the field below which the contribution to initial magnetization is mainly from domain wall displacements. M-ZFC increases with increasing temperature as long as H-cr is greater than the applied field and the applied magnetic field overcomes this critical field above T-p. The results indicate that there is a direct correlation between the shapes of M-ZFC(T) curves and the domain structure of a material. A drastic decrease of M-ZFC below T-p is observed for high coercivity (hard) materials when measured with small DC magnetic fields, compared to a broad maximum obtained for the soft materials, because of domain wall pinning effects. (C) 2000 Elsevier Science B.V. All rights reserved.