Anticollinear magnetic order induced by impurities in the frustrated Heisenberg model of pnictides

TL;DR

This study uses Monte Carlo simulations to explore how non-magnetic impurities affect magnetic ordering in a frustrated Heisenberg model relevant to iron pnictides, revealing impurity-induced anticollinear order and phase transitions.

Contribution

It demonstrates that impurities suppress entropy-driven order-by-disorder and stabilize a new magnetic order, leading to re-entrant phase transitions in the model.

Findings

Impurities quench the entropy-driven phase transition.

A new impurity-stabilized magnetic order emerges.

Re-entrant phase transitions are observed due to impurities.

Abstract

We present Monte Carlo simulations for a classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice in the presence of non-magnetic impurities. We show that the order-by-disorder entropy selection, associated with the Ising-like phase transition that appears for $J_2/J_1>1/2$ in the pure spin model, is quenched at low temperature due to the presence of non-magnetic impurities. Evidences that a new competing order is stabilized around the impurities, and in turn induces a re-entrance phase transition are reported. Implications for local magnetic measurement of the parent compound of iron pnictides are briefly discussed.