Butterfly hysteresis loop at non-zero bias field in antiferromagnetic molecular rings: cooling by adiabatic magnetization

TL;DR

This paper reports the observation of a butterfly-shaped hysteresis loop in the magnetization of NaFe6 molecular rings at low temperatures, indicating potential for cooling via adiabatic magnetization due to level-crossing behavior.

Contribution

It introduces the first observation of butterfly hysteresis at non-zero bias in antiferromagnetic molecular rings and analyzes it with a dissipative two-level model.

Findings

Hysteretic butterfly-shaped loop observed at level-crossing

Unusual features linked to dissipative two-level dynamics

Potential for cooling by adiabatic magnetization at non-zero bias

Abstract

At low temperatures, the magnetization of the molecular ferric wheel NaFe$_6$ exhibits a step at a critical field $B_c$ due to a field-induced level-crossing. By means of high-field torque magnetometry we observed a hysteretic behavior at the level-crossing with a characteristic butterfly shape which is analyzed in terms of a dissipative two-level model. Several unusual features were found. The non-zero bias field of the level-crossing suggests the possibility of cooling by adiabatic magnetization.