  There are two methods of preparation of ferrimagnetic spinel. If, during the
preparation, an external magnetic field as high as 300 O\"{e} is applied upon
cooling the material is named field-cooled (FC). If the applied field is about
1O\"{e} 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.
