Paper detail

Model for the FC and ZFC Ferrimagnetic Spinel

There are two methods of preparation of ferrimagnetic spinel. If, during the preparation, an external magnetic field as high as 300 Oë is applied upon cooling the material is named field-cooled (FC). If the applied field is about 1Oë the material is zero-field cooled (ZFC). To explore the magnetic and thermodynamic properties of these materials we consider two-sublattice spin system, defined on the bcc lattice, with spin-$s^A$ operators $\bf{S_{i}^A}$ at the sublattice $A$ site and spin-$s^B$ operators $\bf{S_{i}^B}$ at the sublattice $B$ site, where $s^A>s^B$. The subtle point is the exchange between sublattice A and B spins, which is antiferromanetic. Applying magnetic field along the sublattice A magnetization, during preparation of the material, one compensates the Zeeman splitting, due to the exchange, of sublattice B electrons. This effectively leads to a decrease of the $s^B$ spin. We consider a model with $s^B$ varying parameter which accounts for the applied, during the preparation, magnetic field. It is shown that the model agrees well with the observed magnetization-temperature curves of zero field cooled (ZFC) and non-zero field cooled (FC) spinel ferrimagnetic spinel and explains the anomalous temperature dependence of the specific heat.