Lanczos exact diagonalization study of field-induced phase transition for Ising and Heisenberg antiferromagnets

TL;DR

This study uses exact diagonalization to analyze field-induced phase transitions in 2D Ising and Heisenberg antiferromagnets, revealing first-order and second-order transitions with a spin-flop process in the Heisenberg case.

Contribution

It provides a detailed exact diagonalization analysis of phase transitions in 2D antiferromagnets, distinguishing between Ising and Heisenberg models.

Findings

Ising antiferromagnet exhibits first-order transition

Heisenberg antiferromagnet exhibits second-order transition

Spin-flop process occurs during the second-order transition

Abstract

Using an exact diagonalization treatment of Ising and Heisenberg model Hamiltonians, we study field-induced phase transition for two-dimensional antiferromagnets. For the system of Ising antiferromagnet the predicted field-induced phase transition is of first order, while for the system of Heisenberg antiferromagnet it is the second-order transition. We find from the exact diagonalization calculations that the second-order phase transition (metamagnetism) occurs through a spin-flop process as an intermediate step.