  In this work we present a study of the low temperature magnetic phases of
polycrystalline MnCr$_2$O$_4$ spinel through dc magnetization and ferromagnetic
resonance spectroscopy (FMR). Through these experiments we determined the main
characteristic temperatures: T$_C$ $\sim$41 K and T$_H$ $\sim$18 K
corresponding, respectively, to the ferrimagnetic order and to the low
temperature helicoidal transitions. The temperature evolution of the system is
described by a phenomenological approach that considers the different terms
that contribute to the free energy density. Below the Curie temperature the FMR
spectra were modeled by a cubic magnetocrystalline anisotropy to the second
order, with $K_1$ and $K_2$ anisotropy constants that define the easy
magnetization axis along the <110> direction. At lower temperatures, the
formation of a helicoidal phase was considered by including uniaxial anisotropy
axis along the [1-10] propagation direction of the spiral arrange, with a $K_u$
anisotropy constant. The values obtained from the fittings at 5 K are
$K_1$=-2.3x10$^4$ erg/cm$^3$, $K^2$=6.4x10$^4$ erg/cm$^3$ and $K_u$=7.5x10$^4$
erg/cm$^3$.
