In this work we present a magnetic, structural, and electron spin resonance (ESR) study of the geometrically frustrated ${\text{MnCr}}_2{\text{O}}_4$ spinel in an extended range of $T$ (2–1000 K). At the lowest temperature $\left(T<18\text{K}\right)$ the ESR lineshape is compatible with the coexistence of spiral and ferrimagnetic spin ordering. Above $T_C$ $\left(\approx 41\text{K}\right)$, magnetic susceptibility $\left(\chi \right)$ and ESR intensity coincide with each other showing the typical behavior of a ferrimagnet. From the $\chi \left(T\right)$ vs $T$ dependence, absolute values for the three exchange constants $J_{\text{MnCr}}$, $J_{\text{CrCr}}$, and $J_{\text{MnMn}}$ were determined. Our results indicate that (i) these values are approximately independent of $T$, (ii) the antiferromagnetic direct Cr-Cr exchange is the main interaction, and (iii) $J_{\text{MnMn}}$ is indeed not negligible as compared with $J_{\text{MnCr}}$ and $J_{\text{CrCr}}$. One noticeable anomaly in the temperature dependence of the ESR linewidth is observed at $T\approx 450\text{K}$. This behavior is accounted by a 30% variation in the extrapolated high-temperature linewidth and it is attributed to a crystalline distortion not reported previously. Experiments of high-temperature x-ray diffraction allowed us to associate this distortion to a deformation of the oxygen sublattice. ESR and x-ray results are both compatible with a more symmetric high-temperature structure.

• Received 24 April 2009

DOI:https://doi.org/10.1103/PhysRevB.80.104418