Correlated-electron theory of strongly anisotropic metamagnets

TL;DR

This paper develops a quantum mechanical theory using the Hubbard model and DMFT to understand metamagnetism in strongly anisotropic antiferromagnets, revealing how temperature, magnetic field, and doping influence phase transitions and magnetic properties.

Contribution

It introduces a detailed DMFT-based analysis of metamagnetic transitions in anisotropic antiferromagnets, including effects of doping and temperature on phase behavior.

Findings

Metamagnetic transitions change from first to second order near the Néel temperature.

Doping reduces critical temperatures and fields, and enhances metallicity.

Theoretical results relate to properties of real magnetic materials like FeBr_2 and UPdGe.

Abstract

The microscopic origin of metamagnetism and metamagnetic transitions in strongly anisotropic antiferromagnets is investigated within a quantum mechanical theory of correlated electrons. To this end the Hubbard model with staggered magnetization m_st along an easy axis e in a magnetic field H || e is studied both analytically and numerically within the dynamical mean field theory (DMFT). At intermediate couplings the self-consistent DMFT equations, which become exact in the limit of large coordination number, are solved by finite temperature Quantum Monte Carlo techniques. The temperature and magnetic field dependence of the homogeneous and staggered magnetization are calculated and the magnetic phase diagram is constructed. At half filling the metamagnetic transitions are found to change from first order at low temperatures to second order near the N'eel temperature, implying the existence of a multicritical point. Doping with holes or electrons has a strong effect: the system becomes metallic, the electronic compressibility increases and the critical temperatures and fields decrease. These results are related to known properties of insulating metamagnets such as FeBr_2, metallic metamagnets such as UPdGe, and the giant and colossal magnetoresistance found in a number of magnetic bulk systems.