Muon-spin relaxation investigation of magnetic bistability in a crystalline organic radical compound

TL;DR

This study uses muon-spin relaxation to investigate magnetic bistability and phase transition in an organic radical compound, revealing different magnetic states across structural phases.

Contribution

It demonstrates the magnetic switching at a specific temperature linked to a structural phase transition using muon-spin relaxation and electronic structure calculations.

Findings

Hysteretic magnetic switching at 274 K

Different muon stopping sites in two phases

Disordered magnetic state at low temperature

Abstract

We present the results of a muon-spin relaxation ($\mu^{+}$SR) investigation of the crystalline organic radical compound 4-(2-benzimidazolyl)-1,2,3,5-dithiadiazolyl (HbimDTDA), in which we demonstrate the hysteretic magnetic switching of the system that takes place at $T = 274 \pm 11\,\mathrm{K}$ caused by a structural phase transition. Muon-site analysis using electronic structure calculations suggests a range of candidate muon stopping sites. The sites are numerous and similar in energy but, significantly, differ between the two structural phases of the material. Despite the difference in the sites, the muon remains a faithful probe of the transition, revealing a dynamically-fluctuating magnetically disordered state in the low-temperature structural phase. In contrast, in the high temperature phase the relaxation is caused by static nuclear moments, with rapid electronic dynamics being motionally narrowed from the muon spectra.