中文摘要：

以CoFeB/MgO为核心单元的垂直各向异性薄膜体系和相关的垂直磁隧道结已获得广泛研究,其中CoFeB的B含量基本都保持为原子比20%.本文采用磁控溅射制备了Ta/（Co0.5Fe0.5）1-xBx/MgO三明治结构及生长顺序相反的系列薄膜,并在573—623K进行真空退火,研究了样品垂直各向异性随B成分的变化.结果显示,当B含量减小到10%时,Ta/CoFeB/MgO体系的垂直各向异性明显降低;相反,当B含量增加至30%时,该体系的垂直各向异性明显增强;发现在高B含量的情形下,样品的垂直各向异性大小与温度稳定性均与三明治结构的生长顺序密切相关;获得了具有优异温度稳定性的垂直磁化MgO/CoFeB/Ta样品.结果表明适当增加B含量是增强CoFeB/MgO体系垂直各向异性和温度稳定性的有效途径之一.

英文摘要：

The discovery of perpendicular magnetic anisotropy（PMA） in Ta/CoFeB/MgO film and the demonstration of high performance perpendicular magnetic tunnel junction（p-MTJ） based on this material system have accelerated the development of the next-generation high-density non-volatile memories and other spintronic devices. Currently it is urgently needed to improve the interfacial PMA and thermal stability of the CoFeB/MgO system for practical applications. So far, the perpendicularly magnetized CoFeB/MgO films and the corresponding p-MTJs have been extensively explored with the B content of the CoFeB layer mostly fixed at about 20 atomic percent. In this paper, four sets of multilayered films Ta/（Co0.5Fe0.5）1-xBx/MgO（x = 0.1, 0.2, 0.3） and MgO/（Co0.5Fe0.5）0.7B0.3/Ta with different CoFeB thickness are deposited on thermally oxidized Si substrates by magnetron sputtering at room temperature,and subsequently they are annealed in high vacuum at different temperatures ranging from 573 to 623 K. The room temperature magnetic properties of the annealed samples are characterized by using vibrating sample magnetometer and superconducting quantum interference device magnetometer.With normal B content of 20% for the CoFeB layer, the Ta/CoFeB/MgO structure annealed at 573 K shows perpendicular magnetization when the CoFeB layer is no thicker than 1.2 nm. As the B content decreases to 10%, it has been found that PMA is achieved only in the sample with a 0.8 nm CoFeB layer under the same annealing condition. The result shows that the interfacial PMA appreciably falls off when the B content is reduced by half. On the other hand,when the B content of the CoFeB layers increases from 20% to 30%, the Ta/CoFeB/MgO structure annealed at 573 K exhibits PMA with the CoFeB layer as thick as 1.4 nm and the interfacial PMA（Ks） increases from 1.7 × 10（-3）J·m（-2）to1.9×10（-3）J·m（-2）together with slightly improved thermal stability. Most remarkably, the MgO/CoFeB/Ta structure with30% B shows optimum anneali