Magnetic vortex effects on first-order reversal curve (FORC) diagrams for greigite dispersions
Magnetic vortex effects on first-order reversal curve (FORC) diagrams for greigite dispersions
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DOI：
10.1016/j.epsl.2018.08.027
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发表时间：
2018-11
影响因子：
5.3
通讯作者：
Miguel A. Valdez-Grijalva;A. Muxworthy;W. Williams;Pádraig Ó Conbhuí;L. Nagy;A. Roberts;D. Heslop
中科院分区：
文献类型：
--
作者：
Miguel A. Valdez-Grijalva;A. Muxworthy;W. Williams;Pádraig Ó Conbhuí;L. Nagy;A. Roberts;D. Heslop
一阶反转曲线(FORC)图在地球物理中被越来越多地用于磁畴状态识别。磁性粒子的磁区状态对粒子大小高度敏感，有关磁粒子的磁区状态的力场图提供了有价值的信息。然而，在许多系统中，天然剩余磁化的主要载体--非均匀磁化粒子的力信号仍然鲜为人知。通过微磁学计算，研究了均匀单磁区(SD)到非均匀单涡(SV)尺寸范围内无相互作用的无规取向的绿云母(Fe3 S 4)分散体的性质。SD粒子(<；50 nm)的信号被发现与以前的SD相干旋转研究非常一致。确定了一个从∼50 nm到∼80 nm的过渡范围，在这个范围内，SD和SV的混合行为产生了复杂的力图。>；∼80 nm粒子具有纯SV行为，系综中所有粒子的剩余态都处于SV态。结果表明，对于SV系综而言，Forc图提供了涡旋成核场和湮灭场的图，并且Forc分布峰值不应被解释为样品的矫顽力，而应解释为饱和路径上的涡旋湮灭场。
First-order reversal curve (FORC) diagrams are used increasingly in geophysics for magnetic domain state identification. The domain state of a magnetic particle is highly sensitive to particle size, about which FORC diagrams provide valuable information. However, the FORC signal of particles with nonuniform magnetisations, which are the main carrier of natural remanent magnetisations in many systems, is still poorly understood. In this study, the properties of non-interacting, randomly oriented dispersions of greigite (Fe 3 S 4) in the uniform single-domain (SD) to non-uniform single-vortex (SV) size range are investigated via micromagnetic calculations. Signals for SD particles (< 50 nm) are found to be in excellent agreement with previous SD coherent-rotation studies. A transitional range from∼ 50 nm to∼ 80 nm is identified for which a mixture of SD and SV behaviour produces complex FORC diagrams. Particles>∼ 80 nm have purely SV behaviour with the remanent state for all particles in the ensemble in the SV state. It is found that for SV ensembles the FORC diagram provides a map of vortex nucleation and annihilation fields and that the FORC distribution peak should not be interpreted as the coercivity of the sample, but as a vortex annihilation field on the path to saturation.