Dynamics of a magnetic particle in an oscillating magnetic field

IF 2.5 3区 物理与天体物理 Q2 PHYSICS, FLUIDS & PLASMAS Physical Review Fluids Pub Date : 2024-07-26 DOI:10.1103/physrevfluids.9.074303
I. Misra, V. Kumaran
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Abstract

The orientation dynamics of and the torque fluctuations due to a spheroidal magnetic particle in an oscillating magnetic field are analyzed in the Stokes flow regime. For a permanent dipole, the dynamics depends on ω, the ratio of the magnetic field frequency, and the viscous relaxation rate. For ω1, the particle executes oscillations with amplitude (ω)1 about its initial orientation. The average torque is zero because the particle does not execute complete rotations, and the root mean square of the torque fluctuations scaled by the characteristic magnetic torque tends to a constant in this limit. For ω1, the orientation is close to the magnetic field direction for most of the oscillation period, and it rapidly rotates when the field passes through extrema. The scaled root mean square of the torque fluctuations is proportional to (ω)1/2 in this limit. The particle orientation aligns along the magnetic field direction for different models of induced dipoles if the magnetization is nonhysteretic. For the hysteretic Stoner-Wohlfarth model, the dynamics also depends on the parameter h0, the ratio of the Zeeman energy, and the anisotropy energy. For h01, the magnetic moment oscillates about one pole of the orientation vector, and the orientation vector rapidly rotates when the field passes through extrema in a manner similar to that for a permanent dipole. For h01, the magnetic moment switches between the two poles of the orientation vector, and the orientation vector executes small amplitude oscillations about the field direction. There is a discontinuous transition between the oscillating and switching magnetic moment which depends on h0 and the initial orientation.

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振荡磁场中的磁性粒子动力学
在斯托克斯流制度下,分析了振荡磁场中球形磁性粒子的取向动力学和扭矩波动。对于永久偶极子,动态取决于ω†、磁场频率比和粘性弛豫率。对于 ω†≫1,粒子以振幅 ∼(ω†)-1 围绕其初始方向摆动。由于粒子不会进行完全旋转,因此平均转矩为零,在此极限下,转矩波动的均方根与特征磁转矩的比例趋于恒定。对于ω†≪1,在振荡周期的大部分时间里,方向接近磁场方向,当磁场通过极值时,方向迅速旋转。在此极限下,转矩波动的均方根比例与 (ω†)-1/2 成正比。如果磁化是非滞后的,那么对于不同的感应偶极子模型,粒子方向会沿着磁场方向排列。对于滞磁性斯通纳-沃尔法特模型,动力学还取决于参数 h0、泽曼能和各向异性能的比值。当 h0≪1 时,磁矩围绕取向矢量的一个磁极摆动,当磁场通过极值时,取向矢量迅速旋转,其方式与永久偶极类似。当 h0≫1 时,磁矩在取向矢量的两极之间切换,取向矢量围绕磁场方向做小振幅振荡。磁矩振荡和切换之间存在不连续的过渡,这取决于 h0 和初始方位。
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来源期刊
Physical Review Fluids
Physical Review Fluids Chemical Engineering-Fluid Flow and Transfer Processes
CiteScore
5.10
自引率
11.10%
发文量
488
期刊介绍: Physical Review Fluids is APS’s newest online-only journal dedicated to publishing innovative research that will significantly advance the fundamental understanding of fluid dynamics. Physical Review Fluids expands the scope of the APS journals to include additional areas of fluid dynamics research, complements the existing Physical Review collection, and maintains the same quality and reputation that authors and subscribers expect from APS. The journal is published with the endorsement of the APS Division of Fluid Dynamics.
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