Realization of perpendicular anisotropy by controlling the interaction between magnetic particles in nanocomposite films

在Ar和N气氛中反应溅射Co和Ti，然后在真空中进行热处理，制备了Co-TiN纳米复合薄膜。研究了钛含量、铂加入量和退火温度对合金显微组织和磁性能的影响。结果表明，沉积的薄膜几乎没有表现出铁磁性能。经过适当温度的热处理后，Co-TiN薄膜表现出铁磁性能和垂直磁各向异性。对于钛含量，发现当Co与Ti的摩尔比为1：2时，薄膜的垂直各向异性最佳，最佳的退火温度为800℃。垂直磁各向异性的产生，我们认为是由于薄膜独特的微结构。沉积后的薄膜为柱状结构的非晶态。在热退火过程中，钴颗粒在柱子内部析出。颗粒在垂直于衬底表面的方向上彼此靠近。但在平面方向上，这些粒子是由TiN分隔的。这意味着Co粒子在垂直方向上的相互作用较强，而在面内方向上的相互作用相对较弱。本文还研究了CoPT/AlN层状结构的磁性能，特别是磁各向异性。研究发现，在薄膜热退火后，通过界面约束可以将张应力引入到金属层中，因此，对于这种层状结构，可以诱导垂直磁各向异性。

Co-TiN nanocomposite films have been fabricated by reactive sputtering of Co and Ti in Ar and N atmosphere, and followed by thermal annealing in a vacuum. The effect of Ti content, Pt addition, and annealing temperature on the microstructure and magnetic properties were investigated in this work. It is found that the as deposited films hardly show ferromagnetic performance. After thermal annealing at appropriate temperatures, the Co-TiN films show ferromagnetic performance, and perpendicular magnetic anisotropy. As to the Ti content, it is found that optimum perpendicular anisotropy is obtained when the mole ratio of Co to Ti is 1:2. And the optimum annealing temperature of such films is 800 C. The occurrence of the perpendicular magnetic anisotropy, we consider, is due to the unique microstructure of such films. The as-deposited films are amorphous with columnar structure. During thermal annealing, Co particles precipitate inside the columns. The particles are close with each other in the direction perpendicular to the substrate surface. But in the in-plane directions these particles are separated by TiN. That means the interaction between Co particles in the perpendicular direction is strong and that in the in-plane directions is relatively weak. Thus the film can be easily magnetized in the perpendicular direction, and perpendicular magnetic anisotropy is induced.In this work, the magnetic properties of CoPt/AlN layered-structure, especially the magnetic anisotropy, were also studied. It is found that tensile stress can be introduced to the metal layers by inter facial restriction, after thermal annealing of the films, and for this reason, perpendicular magnetic anisotropy can be induced for such a layered structure.