Magnetic Properties of the Europium Chalcogenides under Hydrostatic Pressure

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Abstract
The magnetic properties of the europium chalcogenides are commonly explained by a ferromagnetic nearest-neighbor exchange which is strongly volume dependent, and an antiferromagnetic next-nearest-neighbor exchange which varies slowly with distance. A qualitative confirmation of this model has been given by different authors who found an increase of the Curie temperatures of EuO and EuS by application of hydrostatic pressure. In the present work, pressure experiments have been extended to include the antiferromagnets EuTe and EuSe. There is no observable shift of the Néel temperatures with pressures up to 4 kbar (resolution 0.1°K for EuTe and 0.01°K for monocyrstalline EuSe). The metamagnetic transition of EuSe at T*=2.5°K to a ferrimagnetic structure is strongly pressure dependent: dT*/dp=−2.7°K/kbar. Measurements of the magnetization and the paramagnetic susceptibility of EuSe under pressure, both independently, indicate an increase of the ferromagnetic component of the order of +0.1kB °K/kbar. It is shown that the molecular field approximation is adequate for EuTe but needs modification in the case of EuSe.