Co基合金垂直磁各向异性薄膜的研究

发布时间：2018-05-31 09:39

本文选题：垂直磁各向异性 + 磁晶各向异性能　；参考：《北京科技大学》2015年博士论文

【摘要】：传统磁存储要实现超高的存储密度就需要进一步减小磁盘中磁性颗粒的尺寸。由于磁性颗粒体积减小到一定程度就会出现超顺磁效应,我们需要使用具有高磁晶各向异性能的磁性材料来确保小尺寸下磁性颗粒的热稳定性。Co基磁性材料一直被当做制备超高密度存储介质的有力候选材料。根据对密排六方Co基磁性材料各向异性能的系统研究,许多Co基磁性材料(如Sm-Co, Co-W, Co-Mo等)的磁晶各向异性能都大于现在硬盘中所使用的磁性材料Co-Cr-Pt。本研究在若干不同的材料体系中成功制备了Co基垂直各向异性磁性薄膜,并对其机理、形貌、微观织构、磁学性能等方面的性质进行了深入系统的研究,还参与了h-BN隔离层磁隧道结制备中薄膜制备工艺优化方面的研究,主要结论如下： (1)在Ru(0002)织构的缓冲层上成功外延生长出了具有优异垂直磁各向异性的SmCo5-xCux薄膜。同时,深入研究了Cu掺杂对SmCo5-xCux薄膜的磁性和微观晶体结构的影响。随着Cu含量的增加,SmCo5-xCux薄膜的居里温度(Tc)大幅下降。SmCo5-xCux具有超高的垂直各向异性能和可以调节的居里温度,这意味着SmCo5-xCux在常温下具有良好的热稳定性,而在高温下易于写入,这种优异的特性使SmCo5-xCux极有望成为一种新型的超高密度热辅助磁记录(HAMR)介质材料。 (2)根据米德马(Miedema)半经典模型计算出Co-W二元合金的晶态与非晶体的热力学形成焓。热力学计算结果表明在W的原子百分比低于17.5%的时候Co-W薄膜更倾向于形成密排六方相。基于热力学计算结果,我们利用磁控溅射系统制备了一系列不同W含量的Co-W薄膜。经过真空热退火,我们成功地增强了Co-W薄膜的垂直矫顽力,同时Co-W薄膜的磁晶各向异性能常数Ku达到了2.1×106erg/cm3。在本研究中Co-W薄膜的垂直矫顽力达到了1147Oe,这大大提高了Co-W材料成为下一代超高密度磁存储材料的可能性。 (3)成功在Ta缓冲层上制备出垂直各向异性的TbFeCo磁性薄膜,并深入研究了底层Ta的厚度对TbFeCo磁性层磁性的影响。我们发现由于磁性钉扎位数量的增长,TbFeCo层的垂直矫顽力会随着Ta层厚度的增加而明显增加。增加Ta层的厚度可以避免TbFeCo层中Tb原子被氧化,从而降低TbFeCo层的饱和磁化强度。当Ta层厚度达到4nm以后,TbFeCo层会有接近于1的剩磁比。 (4)研究利用六方氮化硼(h-BN)作为隔离层的磁隧道结的制备工艺、薄膜形貌与织构优化。最终利用快速热退火的方法制备出具有hcp Co/h-BN/hcp Co三明治结构的磁性薄膜。为以后的微加工制备h-BN隔离层磁隧道结打下了良好的基础。
[Abstract]:Traditional magnetic storage needs to reduce the size of magnetic particles in order to achieve high storage density. As the volume of magnetic particles decreases to a certain extent, there will be superparamagnetic effect. We need to use magnetic materials with high magnetocrystalline anisotropic energy to ensure the thermal stability of magnetic particles at small size. Co-based magnetic materials have been used as a powerful candidate for preparing ultra-high density storage media. Based on the systematic study of anisotropic energy of compact hexagonal Co based magnetic materials, many Co based magnetic materials (such as Sm-Co, Co-W, Co-Mo, etc.) have higher magnetocrystalline anisotropy energy than the Co-Cr-Pts used in the present hard disk. In this paper, the perpendicular anisotropic magnetic thin films on Co substrates have been successfully prepared in several different material systems. The mechanism, morphology, microtexture and magnetic properties of the films have been studied systematically and thoroughly. It also participated in the study on the optimization of thin film preparation in the preparation of h-BN isolation layer magnetic tunnel junction. The main conclusions are as follows: 1) SmCo5-xCux thin films with excellent vertical magnetic anisotropy have been successfully grown on the buffer layer of Ruz0002) texture. At the same time, the effect of Cu doping on the magnetic properties and microstructure of SmCo5-xCux thin films was investigated. With the increase of Cu content, the Curie temperature of SmCo5-xCux thin film decreases significantly. SmCo5-xCux has high vertical anisotropy energy and adjustable Curie temperature, which means that SmCo5-xCux has good thermal stability at room temperature, but easy to write at high temperature. With this excellent property, SmCo5-xCux is expected to be a new type of ultrahigh density thermally assisted magnetic recording (Ham) dielectric material. (2) the enthalpy of formation between crystalline and amorphous of Co-W binary alloy is calculated based on the semiclassical model of Miedemia). The thermodynamic results show that Co-W films tend to form dense hexagonal phase when the atomic percentage of W is less than 17.5%. Based on the thermodynamic results, a series of Co-W films with different W content were prepared by magnetron sputtering system. After vacuum thermal annealing, the vertical coercivity of Co-W thin films has been successfully enhanced, and the magnetocrystalline anisotropy energy constant Ku of Co-W thin films has reached 2.1 脳 10 6 erg / cm 3. In this study, the vertical coercivity of Co-W thin films reaches 1147Oe, which greatly enhances the possibility of Co-W materials becoming the next generation ultra-high density magnetic storage materials. TbFeCo magnetic thin films with vertical anisotropy were successfully prepared on Ta buffer layer, and the effect of the thickness of Ta on the magnetic properties of TbFeCo magnetic layer was studied. It is found that the vertical coercivity of TbFeCo layer increases with the increase of Ta layer thickness due to the increase of the number of magnetic pinning positions. Increasing the thickness of Ta layer can avoid the oxidation of TB atoms in TbFeCo layer, thus reducing the saturation magnetization of TbFeCo layer. When the thickness of Ta layer reaches 4nm, the TbFeCo layer will have a remanent magnetic ratio close to 1. (4) the preparation process of magnetic tunnel junctions using hexagonal boron nitride h-BN as isolation layer and the optimization of film morphology and texture were studied. Finally, magnetic films with hcp Co/h-BN/hcp Co sandwich structure were prepared by rapid thermal annealing. It lays a good foundation for the preparation of h-BN isolation layer magnetic tunnel junctions by micromachining.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.2

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