A model of multidomain thermoremanent magnetization incorporating temperature‐variable domain structure
A model of multidomain thermoremanent magnetization incorporating temperature‐variable domain structure
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结合温变域结构的多域热剩磁模型
DOI：
10.1029/92jb02572
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发表时间：
1993
影响因子：
--
通讯作者：
V. Shcherbakova
中科院分区：
文献类型：
--
作者：
V. Shcherbakov;E. Mcclelland;V. Shcherbakova
用Neel的剩余磁化强度(TRM)理论无法解释多磁畴(MD)磁铁矿中的热剩余磁化强度(TRM)和部分剩余磁化强度(PTRM)的一些基本实验观测结果。我们给出的实验结果表明：(1)pTRM在任何温度下都是相加的；(2)当用ms(T)归一化时，在场H中获得的温度介于t1和t2之间的pTRM在低于t2的零场冷却时减小；(3)热前史对pTRM的强度有很大的影响。这些结果有力地表明，冷却过程中磁畴结构的重组是MD材料获得TRM的主要控制因素。我们进一步发展了McClelland和Sugiura[1987]的方法，其中TRM和PTRM被认为是非平衡态，并且磁畴结构随温度的变化提供了驱动力，使得PTRM在零场冷却时向退磁态转变。在这样的动力学控制系统中，随机元素是必不可少的；在本文中，我们认为提供这种随机元素的物理机制是由于局部晶体缺陷引起的整个颗粒的易磁化轴方向的变化，或者由于磁畴本身的应力效应。热驱动的磁畴结构变化导致磁化强度的局部随机变化，这是由动力学方程控制的。我们的模型是通过考虑立方晶内离散晶胞的磁化强度而发展起来的，该晶胞内的磁性相当均匀，但晶胞之间可能不同，该模型令人满意地解释了我们的实验观察。热史前的强烈效应归因于局域能量极小态谱的存在，MD颗粒的行为被比作自旋玻璃的行为。
There are some fundamental experimental observations of properties of thermoremanent magnetization (TRM) and partial TRM (pTRM) in multidomain (MD) magnetite that cannot be explained by Neel's theories of TRM. We present experimental results that show (1) that pTRMs are additive at any temperature, (2) that a pTRM acquired in field H between temperatures T1 and T2 decreases on zero-field cooling below T2 when normalized by Ms (T), (3) that thermal pre-history has a strong effect on the intensity of a pTRM. These results strongly point to reorganization of domain structure during cooling being the dominant controlling factor in TRM acquisition in MD material. We further develop the approach of McClelland and Sugiura [1987] where TRM and pTRM are considered to be nonequilibrium states, and change in domain structure with changing temperature provides the driving force to allow a pTRM to shift toward the demagnetized state on zero-field cooling, for example. A random element is essential in such a kinetically controlled system; in this paper we consider the physical mechanism providing this random element to be the variation of direction of the easy axis of magnetization throughout the grain due to local crystal defects, or stress effects due to the domains themselves, for example. Thermally driven domain structure changes then cause essentially random local changes of magnetization, which are governed by kinetic equations. Our model is developed by considering the magnetization of discrete cells within a cubic grain chosen to have reasonably uniform magnetic properties within the cell but probably different between cells, and the model satisfactorily explains our experimental observations. The strong effect of thermal prehistory is ascribed to the existence of a spectrum of local energy minima states, and the behavior of an MD grain is likened to that of a spin glass.