Magnetization, ferromagnetic resonance ͑FMR͒, heat capacity, and electrical conductivity of MnCr 2 S 4 spinel single crystals were investigated as a function of temperature and magnetic field. Two anomalies observed in the heat capacity correlate with magnetic phase transformations and their field dependence found in magnetization measurements. The upper anomaly at a temperature of ϳ65 K marks the onset of ferrimagnetic ordering, while the lower one at ϳ4.8 K indicates an additional antiferromagnetic ordering of the A(Mn) sublattice. Below the Curie temperature, magnetization, and FMR measurements revealed a positive magnetocrystalline anisotropy. The dominating role of the B(Cr) sublattice in generating this anisotropy is shown.

A detailed study of the electronic transport and magnetic properties of Fe 1Ϫx Cu x Cr 2 S 4 (xр0.5) on single crystals is presented. The resistivity is investigated for 2рTр300 K in magnetic fields up to 140 kOe and under hydrostatic pressure up to 16 kbar. In addition magnetization and ferromagnetic resonance ͑FMR͒ measurements were performed. FMR and magnetization data reveal a pronounced magnetic anisotropy, which develops below the Curie temperature, T C , and increases strongly towards lower temperatures. Increasing the Cu concentration reduces this effect. At temperatures below 35 K the magnetoresistance, M Rϭ͓(0) Ϫ(H)͔/(0), exhibits a strong dependence on the direction of the magnetic field, probably due to an enhanced anisotropy. Applying the field along the hard axis leads to a change of sign and a strong increase in the absolute value of the magnetoresistance. On the other hand the magnetoresistance remains positive down to lower temperatures, exhibiting a smeared out maximum with the magnetic field applied along the easy axis. The results are discussed in the ionic picture using a triple-exchange model for electron hopping as well as a half metal utilizing a band picture.

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