Temperature evolution of the effective magnetic anisotropy in the MnCr sub(2)O sub(4) spinel

In this work, we present a study of the low temperature magnetic phases of polycrystalline MnCr sub(2)O sub(4) spinel through dc magnetization and ferromagnetic resonance spectroscopy (FMR). Through these experiments, we determined the main characteristic temperatures: T sub(C) ~ 41K and T sub(H) ~ 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 sub(1) and K sub(2) anisotropy constants that define the easy magnetization axis along the direction. At lower temperatures, the formation of a helicoidal phase was considered by including uniaxial anisotropy axis along the [1 1 0] propagation direction of the spiral arrange, with a K sub(u) anisotropy constant. The values obtained from the fittings at 5 K are K sub(1) = -2.3 x 10 super(4) erg cm super(-3), K sub(2) = 6.4 x 10 super(4) erg cm super(-3) and K sub(u) = 7.5 x 10 super(4) erg cm super(-3).