  Spinel structured compounds, $AB_2O_4$, are special because of their exotic
multiferroic properties. In $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$), a switchable
polarization has been observed experimentally due to a non-collinear magnetic
spin order. In this article, we demonstrated the microscopic origin behind such
magnetic spin order, hysteresis, polarisation and the so-called magnetic
compensation effect in $ACr_2O_4$ ($A$=$Co$, $Mn$,$Fe$, $Ni$) using Monte Carlo
simulation. With a careful choice of the exchange interaction, we were able to
explain various experimental findings such as magnetization vs. temperature (T)
behavior, conical stability, unique magnetic ordering and polarization in a
representative compound $CoCr_2O_4$ which is the best known multiferroic
compound in the $AB_2O_4$ spinel family. We have also studied the effect of
$Fe$-substitution in $CoCr_2O_4$, with an onset of few exotic phenomena such as
magnetic compensation and sign reversible exchange bias effect. These effects
are investigated using an effective interactions mimicking the effect of
substitution. Two other compounds in this family, $CoMn_2O_4$ and $CoFe_2O_4$,
are also studied where no conical magnetic order and polarisation was observed,
as hence provide a distinct contrast. Here all calculations are done using the
polarisation calculated by the spin-current model. This model has certain
limitation and it works quite good for low temperature and low magnetic field.
But the model despite its limitation it can reproduce sign reversible exchange
bias and magnetic compensation like phenomena quite well.
