Theory of partial thermoremanent magnetization in multidomain grains: 2. Effect of microcoercivity distribution and comparison with experiment
Theory of partial thermoremanent magnetization in multidomain grains: 2. Effect of microcoercivity distribution and comparison with experiment
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多畴晶粒部分热剩磁理论：2.微矫顽力分布的影响及与实验的比较
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
D. Dunlop
中科院分区：
文献类型：
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作者：
Song Xu;D. Dunlop
我们扩展的thermoreasticmagnetization（TRM）和pTRM理论在文件1（邓洛普和徐，这个问题）的晶粒中，畴壁钉扎的不同幅度的微磁电阻。假设微电阻率服从指数分布，我们发现总TRM的强度与诱导场H 0成线性比例，对于小的H 0，与大约1-1/n的幂成比例，对于中等的H 0，与H 0无关，对于大的H 0，类似于文献1中得到的结果。这里，n表示作为饱和磁化强度Ms（T）的n次方的微磁化率的温度依赖性。上述三个场依赖区域分别对应于热阻挡、场阻挡和再平衡壁。当被热退磁时，在高场中诱导的TRM具有低的解阻塞温度，如所观察到的。对于从T2（T0）获取的部分TRM，需要甚至更高的T2。在这种情况下，当H 0小时，pTRM的室温强度与H 0 2近似成比例。由此产生的热退磁曲线，归一化到加热前的强度，是独立的H 0和微磁率的平均值。完全退磁不会在退磁温度T2下发生，而仅在接近Tc的温度下发生。该理论得到了实验数据的pTRM测量各种多畴磁铁矿样品的热退磁。
We extend the thermoremanent magnetization (TRM)and pTRM theories developed in paper 1 (Dunlop and Xu, this issue) to grains in which domain walls are pinned by microcoercivities of varying magnitudes. Assuming microcoercivities to be exponentially distributed, we find that the intensity of a total TRM is linearly proportional to the inducing field H0 for small H0, to a power of roughly 1–1/n for intermediate H0, and independent of H0 for large H0, similar to the results obtained in paper 1. Here n represents the temperature dependence of microcoercivity that goes as the n th power of the saturation magnetization Ms (T). The above three field dependent regions correspond to thermally blocked, field-blocked and reequilibrated walls, respectively. When being thermally demagnetized, a TRM induced in a high field has low unblocking temperatures, as observed. For a partial TRM acquired from T2 ( T0, an even higher T2 is required. In such cases, the room temperature intensity of pTRM is approximately proportional to H02 when H0 is small. The resulting thermal demagnetization curve, normalized to the intensity before heating, is independent of both H0 and the mean value of microcoercivities. Complete demagnetization will not occur at a demagnetizing temperature T2 but only at a temperature close to Tc. The theory is supported by experimental data of thermal demagnetizations of pTRMs measured for various multidomain magnetite samples.