Lorentz Microscopy of nano-scale magnetic particles embedded in metal matrices

采用亮场TEM、HRTEM和Lorentz显微镜，结合VSM和SQUID测量，研究了铜基体中纳米级磁性颗粒的畴结构。BFTEM结果表明，共格钴颗粒在50nm处转变为非共格析出相。八面体析出相失去相干性后，进入快速粗化状态。目前的洛伦兹显微镜检测到由于钴粒子的磁化而引起的入射电子束的偏差。偏离角的大小估计为简单洛伦兹力模型的两倍大。Lorentz EM还表明，非相干析出相由四个磁畴组成，每个磁畴的磁化方向为[100]。SQUID测量表明，试样的磁性能遵循超顺磁M-T曲线。但粒子的性质逐渐转变为铁磁性。经过短时间退火后，磁化曲线一度下降。M曲线随退火时间的增加而增大。在两个相干粒子耦合时所达到的最高强制力。

Domain structure of nano-scale magnetic particles embedded in copper matrices were studied by bright-field TEM, HRTEM and Lorentz microscopy, together with VSM and SQUID measurements. BFTEM showed that the coherent cobalt particles were transformed into incoherent precipitates at 50nm in size. After loosing the coherency, the octahedral precipitates entered into rapid coarsening. The present Lorentz microscopy detected the deviation of the incident electron beam due to the magnetization of cobalt particles. The magnitude of the deviating angles was estimated as twice as large as the value derived from a simple Lorentz force model. Lorentz EM also shows that incoherent precipitates were composed of four magnetic domains, each of which has a magnetization oriented to [100].SQUID measurements show that the magnetic properties of the specimens followed in a superparamagnetic M-T curve. But the property of the particles gradually changed into ferromagnetic. The magnetization curve once decreased just after a short annealing. Then the M curve increased with the annealing. The highest coersivity attained at the period that two coherent particles were coupled.