Contribution of spin pairs to the magnetic response in a dilute dipolar ferromagnet

TL;DR

This study uses exact diagonalization of a two-spin Hamiltonian to simulate the magnetic response of a dilute dipolar Ising magnet, revealing the significant role of spin pairs and hyperfine interactions in its behavior.

Contribution

The paper introduces a pairwise model including hyperfine interactions to explain the magnetic susceptibility behavior in a dilute dipolar ferromagnet, highlighting the importance of larger clusters.

Findings

Pairwise model explains susceptibility drop with transverse field.

Hyperfine interactions renormalize crossover fields.

Antiferromagnetic correlations are more significant than expected.

Abstract

We simulate the dc magnetic response of the diluted dipolar-coupled Ising magnet LiHo\(_{0.045}\)Y\(_{0.955}\)F\(_4\) in a transverse field, using exact diagonalization of a two-spin Hamiltonian averaged over nearest-neighbour configurations. The pairwise model, incorporating hyperfine interactions, accounts for the observed drop-off in the longitudinal (c-axis) susceptibility with increasing transverse field; with the inclusion of a small tilt in the transverse field, it also accounts for the behavior of the off-diagonal magnetic susceptibility. The hyperfine interactions do not appear to lead to qualitative changes in the pair susecptibilities, although they do renormalize the crossover fields between different regimes. Comparison with experiment indicates that antiferromagnetic correlations are more important than anticipated based on simple pair statistics and our first-principles calculations of the pair response. This means that larger clusters will be needed for a full description of the reduction in the diagonal response at small transverse fields.