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采用室温沉积高温退火的方式在单晶MgO(001)基片上制备了具有马氏体相变的铁磁Ni-Mn-Ga薄膜。沉积态薄膜呈柱状晶结构,高温退火后柱状晶的晶界变得模糊。溅射气压为0.5Pa和0.2Pa的薄膜的马氏体相变起始温度分别为290K和332K,溅射气压改变了薄膜成分,进而改变了相变温度。根据300K测得的磁化曲线,退火后溅射气压为0.5Pa和0.2Pa的薄膜分别显示出软磁和硬磁特性,这与M-T曲线的结果是相符的。室温下,0.5Pa薄膜的磁畴形貌呈现出迷宫状;而0.2Pa样品则显现出马氏体的浮凸,与它的磁畴形貌直接关联。 相似文献
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During the process of directional solidification, laser remelting/solidification in the layer on sintered magnets, die-upsetting of cast magnets, or die-upsetting of nano-composites, the arrangements of the easy-magnetization-axes of the hard magnetic phases (Nd2Fe14B, SmCo5 or Sm2Co17 type) in their designed directions have been studied. In Fe-Pt nano-composite magnets, attempts have been taken to promote phase transformation from disordered, soft magnetic A1 to ordered, hard magnetic L10 FePt phase at reduced temperatures. The dependence of the magnetization and reversal magnetization processes on the microstructures, involving the morphology and three critical sizes of particles of the FePt nano-composite magnets, are summarized. With the decrease of the nominal thickness of the anisotropic FePt film epitaxially grown on the single crystal MgO (001) substrate, the reversal magnetization process firstly changes from full domain wall displacement to partial magnetic wall pinning related to the morphology change, where the coercive force increases abruptly. The reversal magnetization process secondly changes from magnetic wall pinning to incoherent magnetization rotation associated with the particles being below the first critical size at which multi-domain particles turn into single domain ones, where the coercive force is still increased. And the reversal magnetization mode thirdly changes from incoherent to coherent rotation referred to the second critical size, where the increase of the coercive force keeps on. However, when the particle size decreases to approach the third critical size where the particles turn into the supperparamagnetic state, the coercive force begins to decrease due to the interplay of the size effect and the incomplete ordering induced by the size effect. Meanwhile, due to the size effect, Curie temperature of the ultra-small FePt particles reduces. 相似文献
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