Anomalous breakdown of Bloch's rule in the Mott-Hubbard insulator MnTe2

We reinvestigate the pressure dependence of the crystal structure and antiferromagnetic phase transition in MnTe2 using the rigorous and reliable tool of high-pressure neutron powder diffraction. First-principles density functional theory calculations are carried out in order to gain microscopic insight. The measured Néel temperature of MnTe2 is found to show unusually large pressure dependence of 12KGPa-1. This gives rise to a large violation of Bloch's rule given by α=dlogTNdlogV=-103≈-3.3, to an α value of -6.0±0.1 for MnTe2. The ab initio calculation of the electronic structure and the magnetic exchange interactions in MnTe2 for the measured crystal structures at different pressures indicates the pressure dependence of the Neél temperature α is -5.61, in close agreement with experimental findings. The microscopic origin of this behavior turns out to be dictated by the distance dependence of the cation-anion hopping interaction strength.