Preparation and Characterization of Nitride-base Magnetic nanocomposite films

本文对Co-Ti-N薄膜的制备和表征进行了研究。首先，我们揭示了Co-Ti-N薄膜的制备条件与结构的关系。在Ar+N_2混合气体中对Co-Ti复合靶进行直流溅射，制备了Co-Ti-N薄膜。对于在合适的N_2分压下沉积的薄膜，在沉积后的热退火过程中，Ti和N发生反应生成TiN。结果表明，Co和Ti相互分离，形成Co-TiN纳米复合材料。Co和TiN颗粒的纵向尺寸约为10 nm。沿薄膜表面的法向发展出纤维状结构。其次，研究了Co-TiN纳米复合薄膜的磁性。研究发现，厚度小于100 nm的Co-TiN纳米复合薄膜在纵向和纵向具有相似的磁化行为。然而，那些厚度在…以上的薄膜在100 nm以上表现出垂直磁各向异性，即垂直方向成为磁化的易轴。此外，还研究了热退火条件和薄膜结构对磁性能的影响。沉积前的薄膜几乎没有表现出铁磁性能。在400~700℃的温度范围内，薄膜表现出明显的铁磁性，且饱和磁化强度随退火温度的升高而增大。这是因为在沉积状态下，Co原子与Ti和N原子成键，在高温热退火时，N原子优先与Ti原子反应，因此，Co被分离出来。Co-TiN薄膜的磁性能也强烈地依赖于薄膜中N的含量。当N量太小时，相分离不能完全进行。另一方面，当N量过大时，除Ti外，Co也被氮化。这两种情况都会削弱饱和磁化强度。除了磁性能外，我们还发现Co-TiN纳米复合薄膜的电阻率和硬度都比金属薄膜和合金薄膜高，根据本研究的结果，我们认为Co-TiN基纳米复合薄膜是一种非常有前途的超高密度垂直磁记录介质。较少

In this work, the preparation and characterization of Co-Ti-N films have been conducted. First, we have disclosed the relation between the preparation condition and the structure of the Co-Ti-N films. Co-Ti-N films have been prepared by dc sputtering of Co-Ti complex target in Ar +N_2 gas mixture. For the films deposited at appropriate N_2 partial pressure, the reaction between Ti and N occurs to form TiN during post-deposition thermal anneal. As a result Co and Ti separate with each other, to form Co-TiN nano-composite. The sizes of Co and TiN grains in the longitude direction are about 10 nm in diameter. And fiber-like structure is developed along the normal direction of the film surface. Next the magnetic properties of the Co-TiN nanocomposite films have been investigated. It has been found Co-TiN nanocomposite films with their thickness less than 100 nm show similar magnetization behavior in both longitude and perpendicular directions. However, those films with their thickness abov … More e 100 nm show perpendicular magnetic anisotropy, I.e. perpendicular direction becomes the easy axis of magnetization. Furthermore, the dependence of magnetic properties on the thermal anneal condition and film structure have been investigated. The as-deposited films almost do not show ferromagnetic performance. When the films were annealed at 400 - 700℃, they show clearly ferromagnetic performance and the saturation magnetization increased with increasing anneal temperature. This is because that in the as-deposited state, Co atoms are bonded to Ti and N, upon thermal anneal at elevated temperature, N atoms preferentially react with Ti atoms, therefore, Co is separated. The magnetic properties of the Co-TiN films also depend strongly on the amount of N incorporated into the films. When N amount is too small, the phase separation can not fully proceed. On the other hand, when the N amount is too large, Co is also nitrided except Ti. Both cases will impair the saturation magnetization. Therefore it is important to control the N amount in the film.Beside the magnetic properties, we have found that the resistivity and hardness of Co-TiN nanocomposite films are very high compared with metal and alloy films.According to the result of this research work, we consider the Co-TiN-based nanocomposite films very promising as ultra-high density perpendicular magnetic recording media. Less