取向双稳态和受场控制的超参数磁双极子切换
Orientational bistability and field-controlled switching of a superparamagnetic dimer
AI总结：
研究超参数磁双极子的取向动力学，揭示其在静态磁场下双稳态分布及受场控制的切换机制，通过磁响应分析内部磁结构。
摘要：
我们研究了具有诱导磁矩和有效永久磁矩的超参数磁性胶体双极子的取向动力学。在静态均匀磁场中，固定在一起的双极子在平面内两个优选角度之间跳跃，形成双模稳态取向分布。当相同磁场周期性反转时，我们观察到动态响应从小跳跃事件（Δθ<<π）到每个磁场翻转时全旋转（Δθ≈π）的急剧变化。我们表明，静态双稳态和切换分支可通过双极子中强诱导和弱固定成分的磁响应来解释。这导致了复杂的取向能量/势能景观，双极子的耦合滚转-俯仰旋转负责双稳态动力学。通过结合双极子轴与磁场的偏转、分支场强度和短时间取向方差，我们确定净永久磁偶极矩的大小和方向，从而通过显微镜表征颗粒的内部磁结构细节。
英文摘要：
We study the orientational dynamics of superparamagnetic colloidal dimers that carry both an induced magnetic moment, proportional to the applied field, and an effective permanent moment. In a static, uniform magnetic field, dimers that are permanently fixed together hop between two preferred in-plane angles, developing a bimodal steady-state orientation distribution. When the same field is periodically reversed, we observe a sharp, field-controlled change in the dynamical response from small hopping events with $Δθ\ll π$ to full $Δθ\approx π$ rotations on each field flip. We show that both the static bistability and the switching bifurcation can be rationalised by a magnetic response in the dimer that consists of both a strong induced and weak body-fixed component. This leads to a complex orientational energy/potential landscape, with coupled roll-yaw rotations of the dimer responsible for the bistable dynamics. By combining the misorientation between dimer axis and field, bifurcation field strength and short-time orientational variance, we determine the magnitude and orientation of the net permanent dipole, thereby characterising details of the internal magnetic structure of the particles via microscopy.
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