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

TL;DR

This study investigates the pressure-induced anomalous breakdown of Bloch's rule in MnTe₂, revealing a significant deviation in the Neél temperature's pressure dependence explained by microscopic electronic interactions.

Contribution

It combines high-pressure neutron diffraction and first-principles calculations to explain the unusual pressure dependence of the Neél temperature in MnTe₂, highlighting the role of cation-anion interactions.

Findings

Neél temperature shows a large pressure dependence of 12 K GPa$^{-1}$

Bloch's rule is significantly violated in MnTe₂, with α ≈ -6.0

Theoretical calculations agree with experimental pressure dependence of T_N

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 N\'eel 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 Ne\'el 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.