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We have conducted high-pressure X-ray diffraction studies on the MnCr 2 O 4 and NiCr 2 O 4 spinels at room temperature. Both compounds undergo pressure-induced structural transitions into diverse tetragonal modifications. Based on these experimental observations and our ab initio calculations, we show that the Cr-oxide spinels with magnetic A 2+ cations (A 2+ = Mn, Fe, Co, Ni) follow a similar trend as their chalcogenide counterparts with non-magnetic A 2+ ions, i.e. the transition pressure is proportionally related with the magnitude of the Cr-Cr magnetic exchange interactions. Therefore, we reach the conclusion that the Cr-Cr magnetic exchange interactions alone suffice to account for the high-pressure behavior of these systems. Our results clearly depict the close relationship between the structural and magnetic degrees of freedom in Cr-bearing spinels.

Through calculation and analysis of the dynamic and electronic properties of 3d rocksalt transition metal carbides, we identify MnC as a novel material displaying ferromagnetic superconductivity mediated by minority-spin-triplet Cooper pairs.

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