Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical

TL;DR

This study investigates the nonlinear magnetic responses of Mn12 single-molecule magnets, revealing their sensitivity to anisotropy and quantum effects, and estimates decoherence times from experimental data.

Contribution

It provides the first detailed experimental analysis of both equilibrium and dynamical nonlinear susceptibilities in Mn12 magnets, highlighting quantum effects and relaxation mechanisms.

Findings

Nonlinear susceptibility is sensitive to magnetic anisotropy.

Large nonlinear dynamic response with peaks reversed relative to classical models.

Estimated decoherence time bound from quantum detuning analysis.

Abstract

We present an experimental study of the {\em nonlinear} susceptibility of Mn$_{12}$ single-molecule magnets. We investigate both their thermal-equilibrium and dynamical nonlinear responses. The equilibrium results show the sensitivity of the nonlinear susceptibility to the magnetic anisotropy, which is nearly absent in the linear response for axes distributed at random. The nonlinear dynamic response of Mn$_{12}$ was recently found to be very large and displaying peaks reversed with respect to classical superparamagnets [F. Luis {\em et al.}, Phys. Rev. Lett. {\bf 92}, 107201 (2004)]. Here we corroborate the proposed explanation -- strong field dependence of the relaxation rate due to the detuning of tunnel energy levels. This is done by studying the orientational dependence of the nonlinear susceptibility, which permits to isolate the quantum detuning contribution. Besides, from the analysis of the longitudinal and transverse contributions we estimate a bound for the decoherence time due to the coupling to the phonon bath.