Magnetocrystalline interactions in MnCr2O4 spinel

E. WINKLER; S. CANOSA BLANCO; M.A. LÓPEZ QUINQUELA; J. RIVAS; A. CANEIRO; M.T. CAUSA; M. TOVAR

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Año: 2009 vol. 80 p. 1044181 - 1044188

1098-0121

In this work we present a magnetic, structural, and electron spin resonance
ESR study of the geometricallyfrustrated MnCr2O4 spinel in an extended range of T
2–1000 K. At the lowest temperature
T
18 Kthe ESR lineshape is compatible with the coexistence of spiral and ferrimagnetic spin ordering. Above TC
41 K, magnetic susceptibility
 and ESR intensity coincide with each other showing the typical behaviorof a ferrimagnet. From the 
T vs T dependence, absolute values for the three exchange constants JMnCr, JCrCr,and JMnMn were determined. Our results indicate that
i these values are approximately independent of T,
iithe antiferromagnetic direct Cr-Cr exchange is the main interaction, and
iii JMnMn is indeed not negligible ascompared with JMnCr and JCrCr. One noticeable anomaly in the temperature dependence of the ESR linewidthis observed at T450 K. This behavior is accounted by a 30% variation in the extrapolated high-temperaturelinewidth and it is attributed to a crystalline distortion not reported previously. Experiments of hightemperaturex-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.