Origin of anomalous breakdown of Bloch's rule in the Mott-Hubbard insulator MnTe${}_2$

Abstract

We reinvestigate the pressure dependence of the crystal structure and antiferromagnetic phase transition in MnTe${}_2$ by 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 MnTe${}_2$ is found to show unusually large pressure dependence of $12$ K GPa${}^{-1}$. This gives rise to large violation of Bloch's rule given by $\alpha =\frac{d\log T_N}{d\log V}=-\frac{10}{3}\approx -3.3$, to a $\alpha$ value of -6.0 $\pm$ 0.1 for MnTe${}_2$. The ab-initio calculation of the electronic structure and the magnetic exchange interactions in MnTe${}_2$, for the measured crystal structures at different pressures, gives the pressure dependence of the Neél temperature, $\alpha$ to be -5.61, in close agreement with experimental finding. The microscopic origin of this behavior turns to be dictated by the distance dependence of the cation-anion hopping interaction strength.