铁磁材料的涨落耗散考虑和阻尼模型

Conformation dependent damping and generalization of fluctuation-dissipation relation

Damping on an object generally depends on its conformation (shape size etc.). We consider the Langevin dynamics of a model system with a conformation dependent damping and generalize the fluctuation dissipation relation to fit in such a situation. We derive equilibrium distribution function for such a case which converges to the standard Boltzmann form at the limit of uniform damping. The results can have implications, in general, for barrier overcoming processes where standard Boltzmann statistics is slow.

Generalized fluctuation-dissipation relation and statistics for the equilibrium of a system with conformation dependent damping

Liouville's theorem, based on the Hamiltonian flow (micro-canonical ensemble) for a many particle system, indicates that the (stationary) equilibrium probability distribution is a function of the Hamiltonian. A canonical ensemble corresponds to a micro-canonical one at thermodynamic limit. On the contrary, the dynamics of a single Brownian particle (BP) being explicitly non-Hamiltonian with a force and damping term in it and at the other extreme to thermodynamic limit admits the Maxwell-distribution (MD) for its velocity and Boltmann-distribution (BD) for positions (when in a potential). This …

Linking fluctuation and dissipation in spatially extended out-of-equilibrium systems

For systems in equilibrium at a temperature $T$, thermal noise and energy damping are related to $T$ through the fluctuation-dissipation theorem (FDT). We study here an extension of the FDT to an out of equilibrium steady state: a microcantilever subject to a constant heat flux. The resulting thermal profile in this spatially extended system interplays with the local energy dissipation field to prescribe the amplitude of mechanical fluctuations. Using three samples with different damping profiles (localized or distributed), we probe this approach and experimentally demonstrate the link between…

铁磁体中辐射诱导的Landau-Lifshitz-Gilbert阻尼

Radiation Induced Landau-Lifshitz-Gilbert Damping in Ferromagnets

自旋波铁磁共振分析中所采用的Landau-Lifshitz-Gilbert阻尼系数与样品的电导率有关。变化的磁化（随时间）辐射电磁场。然后，电磁能量被样品吸收，并且所产生的加热效应描述了磁耗散阻尼。铁磁共振弛豫速率理论上取决于样品的几何形状（形状和尺寸）以及与实验一致的温度。

Asymmetric Langevin dynamics for the ferromagnetic spherical model

The present work pursues the investigation of the role of spatial asymmetry and irreversibility on the dynamical properties of spin systems. We consider the ferromagnetic spherical model with asymmetric linear Langevin dynamics. Such an asymmetric dynamics is irreversible, i.e., breaks detailed balance, because the principle of action and reaction is violated. The fluctuation-dissipation theorem therefore no longer holds. The stationary state is however still Gibbsian, i.e., the weights of configurations are given by the Boltzmann factor corresponding to the ferromagnetic Hamiltonian. The mode…

二维铁磁XY模型中的自旋波阻尼

Spinwave damping in the two-dimensional ferromagnetic XY model

研究了二维经典铁磁XY模型中自旋波的阻尼效应。阻尼率$Γ_{q}$的计算，由于四阶偏差的谐波自旋哈密顿使用的领导图。由此产生的四维积分的评估扩展的技术开发的Gilat和其他谱密度类型的积分。由于Reiter和Solander以及Menezes，$Γ_{q}$被包括在记忆函数形式中，以确定动态结构函数$S(q,ω)$。对于无限大的系统，记忆函数的方法被发现给非发散的自旋波峰，和一个平滑的非零的背景强度（“高原”或分布强度）的整个范围内的频率低于自旋波峰。相对于自旋波峰值的背景振幅随温度升高而升高，并最终变得高于自旋波峰值，在自旋波峰值处，背景振幅出现为中心峰值。对于有限尺寸的系统，在自旋波峰的两侧存在多个弱峰序列，其数量和位置取决于系统尺寸和波矢（以$2π/L$为整数单位）。这些动力学的有限尺寸效应解释的记忆功能分析，由于自旋波的差异过程低于自旋波峰或求和过程以上的自旋波峰。这些特征在经典的MonteCarlo-自旋动力学模拟中也被发现。