摘要:
应用磁控溅射法在玻璃基片上制备了以Pt为底层的CoFeB/Ni多层膜结构样品,通过测试样品的反常霍尔效应研究多层膜的垂直磁各向异性(perpendicular magnetic anisotropy, PMA),对影响多层膜垂直磁各向异性的各因素进行了调制.实验结果表明,多层膜的底层厚度、周期层中各层的厚度及周期数对样品的反常霍尔效应和磁性有重要影响.通过对样品各参数的逐步调制,最终获得了具有良好PMA的CoFeB/Ni多层膜最佳样品Pt(4)/[CoFeB(0.4)/Ni(0.3)]3/Pt(1.0).经测试计算,该样品的各向异性常数Keff为2.2×106 erg/cm3(1 erg/cm3=10?1 J/m3),具有良好的PMA 性能,样品总厚度为7.1 nm,完全满足制备垂直磁结构材料的厚度要求,可进一步研究其在器件中的集成与应用.
Abstract:
The CoFeB/Ni multilayers with Pt underlayer are prepared by magnetron sputtering technique and the perpen-dicular magnetic anisotropy (PMA) of each of the samples is studied by anomalous Hall effect (AHE) method. The PMA of CoFeB/Ni multilayer is dependent on the thickness of Pt, Co, CoFeB and the number of CoFeB/Ni bilayers strongly. It is found that the sample structured as Pt(4)/[CoFeB(tCoFeB)/Ni(0.3)]2/Pt(1.0) has a good PMA when the CoFeB thickness is 0.4 nm for the interface anisotropy dominated in the multilayer. So the CoFeB thickness is fixed at 0.4 nm. The effect of Ni thickness on multilayer PMA is also studied. The PMA of the sample is kept relatively well and the Hall resistance (RHall) decreases as the Ni thickness increases. Meanwhile the coercivity (HC) fluctuates in a small range. When the Ni thickness is 0.3 nm, the remanence squareness of the sample is very good and the Hall effect is strongest. The influence of period number n on the sample PMA is significant for it changes the interface of the sample. When n is 3, the sample has a very good remanence squareness, for the interface effect is obvious and the magnetization reversal process is consistent. The Pt underlayer shows a great effect on the PMA performance of the sample, for it can change the (111) texture of the multilayer. The results show that when the Pt thickness is 4 nm, the remanence squareness is good and the sample has a suitable HC. So the optimum CoFeB/Ni multilayer with an excellent performance of PMA is structured as Pt(4)/[CoFeB(0.4)/Ni(0.3)]3/Pt(1.0). Its anisotropy constant Keff is 2.2 × 106 erg/cm3 (1 erg/cm3 = 10?1 J/m3) which indicates that the sample has an excellent PMA and its interface anisotropy is the main reason for making the Keff have a larger value. The magnetic layer thickness of the optimum sample is 2.1 nm and the total thickness of it is less than 8 nm. The integration with device can be studied further. Furthermore, HC of the CoFeB/Ni multilayer is relatively small and can be increased by inserting the oxidation layer or other ways.
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