Nonlinear response of single-molecule nanomagnets:: Equilibrium and dynamical -: art. no. 224433
Nonlinear response of single-molecule nanomagnets:: Equilibrium and dynamical -: art. no. 224433
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DOI：
10.1103/physrevb.72.224433
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发表时间：
2005-12-01
影响因子：
3.7
通讯作者：
García-Palacios, JL
中科院分区：
文献类型：
--
作者：
López-Ruiz, R;Luis, F;García-Palacios, JL
本文对Mn-12单分子磁体的非线性磁化率进行了实验研究。我们研究了它们的热平衡和动力学非线性响应。平衡结果表明，非线性磁化率的磁各向异性的敏感性，这是几乎不存在的轴随机分布的线性响应。最近发现Mn-12的非线性动态响应非常大，显示出与经典超顺磁体相反的峰[F. Luis，Phys. Rev. Lett. 92，107201（2004）]。在这里，我们证实了所提出的解释-强场依赖的弛豫速率由于失谐的隧道能级。这是通过研究非线性极化率的取向依赖性，这使我们能够隔离量子失谐的贡献。此外，从纵向和横向的贡献的分析，我们估计的边界的退相干时间由于耦合到声子浴，这是远远短于能级寿命。
We present an experimental study of the 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, displaying peaks reversed with respect to classical superparamagnets [F. Luis , Phys. Rev. Lett. 92, 107201 (2004)]. Here we corroborate the proposed explanation-the 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 us 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, which is much shorter than the energy-level lifetimes.