Revealing the degree of magnetic frustration by non-magnetic impurities

TL;DR

This paper proposes using magnetic field imaging around non-magnetic impurities to quantify magnetic frustration levels in models relevant to iron pnictides, revealing distinct behaviors in different frustrated systems.

Contribution

It introduces a method to distinguish magnetic frustration degrees via impurity-induced local magnetic responses in specific models.

Findings

Bound magnons trap near impurities in the $J_1$-$J_2$ model.

Local moments are enhanced near impurities in the $J_{1a}$-$J_{1b}$-$J_2$ model.

Experimental techniques can test these theoretical predictions.

Abstract

Imaging the magnetic fields around a non-magnetic impurity can provide a clear benchmark for quantifying the degree of magnetic frustration. Focusing on the strongly frustrated $J_1$-$J_2$ model and the spatially anisotropic $J_{1a}$-$J_{1b}$-$J_2$ model, very distinct low energy behaviors reflect different levels of magnetic frustration. In the $J_1$-$J_2$ model, bound magnons appear trapped near the impurity in the ground state and strongly reduce the ordered moments for sites proximal to the impurity. In contrast, local moments in the $J_{1a}$-$J_{1b}$-$J_2$ model are enhanced on the impurity neighboring sites. These theoretical predictions can be probed by experiments such as nuclear magnetic resonance and scanning tunneling microscopy, and the results can elucidate the role of frustration in antiferromagnets and help narrow the possible models to understand magnetism in the iron pnictdies.