Ni/Cr多层膜的磁各向异性

MAGNETIC ANISOTROPY OF Ni/Cr MULTILAYERS

利用振动样品磁强计（ＶＳＭ）和铁磁共振仪（ＦＭＲ）研究了Ｎｉ／Ｃｒ多层膜的磁各向异性．通过对ＦＭＲ谱拟合，我们得到的界面各向异性常数值大于０．这种正的界面各向异性常数将有利于磁化强度的取向垂直于膜面．另外，我们还对引起这种垂直各向异性的机制进行了一些讨论．

A series of Ni/Cr periodic multilayers were successfully prepared by using magnetron sputtering and their structures were characterized by x ray diffraction. In the low angle region, Bragg reflections up to third order confirm that the Ni/Cr multilayers were of periodic structure. With the x ray refractive corrections taken into account, the period deduced from these Bragg peaks agrees well with the designed value. The positions of high angle peaks show that the Ni/Cr multilayers were grown with Cr(110) and Ni(111) texture. The interplaner spacing of Cr is smaller than that of bulk Cr, and the interplaner spacing of Ni is larger than tht of the bulk fcc Ni(111) plane. The result indicates a contraction of the Cr lattices and a dilation of the Ni lattices along the growth direction, which results from the lattice mismatch between the Cr and Ni. The magnetic anisotropy of Ni/Cr multilayers has been investigated using vibrating sample magnetormeter (VSM) and ferromagnetic resonance (FMR) techniques. The magnetic hysteresis loops show that the easy magnetization direction is of easy plane type, and in plane anisotropy decreases with a decreasing of Ni layer thickness, but the perpendicular anidotropy increases with a dereasing of the Ni layer thickness. This result is also obtained by FMR measurement. The FMR spectra are obtained as a function of the orientation of the applied magnetic field from in plane to out of plane. The results are fitted theoretically to determine magnetic anisotropy. From VSM and FRM, a positive value for Ni/Cr interface anisotropy is obtained, which favors a perpendicular easy axis. The possible mechanism for the perpendicular anisotropy has been discussed and it may be attributed to the magnetostriction, caused by intrinsic stress due to lattice mismatch. In addition, a critical Ni layer thickness, below which the easy axis of multilayer switches from in plane to perpendicular to the film plane, can be deduced.