Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical

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.

arXiv comment13 pages, 8 figures, resubmitted to Phys. Rev. B with minor changes

References in corpus (11)

• High frequency EPR spectra of a molecular nanomagnet provide a key to understand Quantum Tunneling of the Magnetization
• Thermally Activated Resonant Magnetization Tunneling in Molecular Magnets: Mn_12Ac and others
• Nuclear spin driven resonant tunnelling of magnetisation in Mn12 acetate
• Thermally activated escape rates of uniaxial spin systems with transverse field
• Nonlinear dynamic susceptibilities of interacting and noninteracting nanoparticle systems
• Relaxation time of weakly interacting superparamagnets
• Spin dynamics of Mn12-acetate in the thermally-activated tunneling regime: ac-susceptibility and magnetization relaxation
• Thermodynamic perturbation theory for dipolar superparamagnets
• Resonant Magnetization Tunneling in Mn12 Acetate: The Absence of Inhomogeneous Hyperfine Broadening
• Nonlinear response of superparamagnets with finite damping: an analytical approach
• Large quantum nonlinear dynamic susceptibility of single-molecule magnets

Cited by in corpus (6)

• Equilibrium susceptibilities of superparamagnets: longitudinal & transverse, quantum & classical
• Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers
• Spin relaxation in phase space
• Quantum and statistical mechanics in open systems: theory and examples
• Stochastic Boltzmann Equation for Magnetic Relaxation in High-Spin Molecules
• Nonlinear ac stationary response and dynamic magnetic hysteresis of quantum uniaxial superparamagnets