Co/Ni多层膜垂直磁各向异性的研究

Perpendicular magnetic anisotropy in Co/Ni multilayers studied by anomalous Hall effect

采用直流磁控溅射法在玻璃基片上制备了Pt底层的Co/Ni多层膜样品,对影响样品垂直磁各向异性的各因素进行了调制,通过样品的反常霍尔效应系统的研究了Co/Ni多层膜的垂直磁各向异性.结果表明,多层膜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的影响.通过对多层膜各个参数的调制优化,最终获得了具有良好的垂直磁各向异性的Co/Ni多层膜最佳样品Pt(2.0)/Co(0.2)/Ni(0.4)/Co(0.2)/Pt(2.0),经计算,该样品的各向异性常数Keff达到了3.6×105J/m3,说明样品具备良好的垂直磁各向异性.最佳样品磁性层厚度仅为0.8 nm,样品总厚度在5 nm以内,可更为深入的研究其与元件的集成性.

Co/Ni multilayers with Pt underlayers have been prepared by magnetron sputtering technique, and their perpen- dicular magnetic anisotropy （PMA） was studied by the anomalous Hall effect （AHE）. The PMA of the samples can be studied by the intensity of Hall signal （RHall）, remanence ratio （Mr/Ms）, coercivity （Hc） and the squareness of the samples in the Hall hysteresis loops. A clear PMA is observed in the as-deposited amorphous Co/Ni multilayers. The PMA of Co/Ni multilayers is strongly dependent on the thicknesses of Pt, Co, and Ni, and the number of Co/Ni bilayers. After testing, the thicknesses of Pt, Co, and Ni, and the periodic number （n） of Co/Ni bilayers are determined to be 2 nm, 0.2 nm, 0.4 nm and 1 respectively. The optimum Co/Ni multilayer with excellent performance of PMA has a structure expressed as Pt（2）/Co（0.2）/Ni（0.4）/Co（0.2）/Pt（2）. The hysteresis loop of the sample with the field applied in plane is tested, showing the characteristics of hard axis typically. PMA can be measured by the anisotropy constant Keff which is determined by the competition of the interface anisotropy to the volume anisotropy. If the interface anisotropy is dominant, the sample will have PMA. The anisotropy constant Keff of Pt（2）/Co（0.2）/Ni（0.4）/Co（0.2）/Pt（2） is 3.6 × 10^5 J/m3, illustrating that it has an excellent PMA, and the interface anisotropy of Co/Ni is the main factor that makes Keff a larger value. Since the thickness of magnetic layer in the optimum sample is only 0.8 nm and the total thickness of it less than 5 nm, the integration of the device can be studied further. Frthermore, the coercivity of an optimum Co/Ni multilayered sample is relatively small and can be increased by inserting an oxidation layer or by other ways.