FePt/FeRh双层薄膜的结构和磁性

Structures and magnetic properties of FePt/FeRh bilayer films

用磁控溅射法,在加热到400℃的Mg O(001)基片上,得到25 nm厚的A1相Fe Pt软磁薄膜,经过热处理使之发生不同程度的A1→L10相转变,在450℃继续生长50 nm厚的Fe Rh,并在相同温度连续保温24 h,使Fe Rh层转变为有序的B2相,得到具有热致反铁磁-铁磁转变性质的Fe Pt/Fe Rh双层复合磁性薄膜.结果表明,Fe Pt层和Fe Rh层都有(001)取向;在生长Fe Rh层之前,如果Fe Pt层没有或者未完全转变为硬磁的L10相,可以使Fe Rh层的反铁磁-铁磁转变温度由100℃提高到200℃;沿垂直于膜面的方向施加磁场,双层薄膜的室温磁化曲线呈方形,矫顽力可达到7.4 k Oe;升温使Fe Rh层转变为软铁磁性,反磁化过程的磁化强度在2个特征磁场附近发生跳跃,显示双层膜中形成了磁性弹簧,矫顽力可下降一半以上.Fe Rh反铁磁-铁磁转变温度升高的原因在于有适量的Pt从Fe Pt层析出并扩散进入Fe Rh层,用于制作热辅助复合垂直磁存储介质,有助于提高稳定性.

Soft A1-FePt （25 nm） films were magnetron-sputtered onto MgO （001） substrates at 400℃ and annealed at different temperatures to adjust the degree of A1→L10 transformation. The FePt was then covered with FeRh （50 nm） film at 450℃ and subsequently annealed at the same temperature for 24 h to transform the FeRh layer into the ordered B2 phase. In this way, near-equiatomic FeRh/FePt bilayer films showing thermal antiferromagnetic-ferromagnetic transition behavior were obtained. The results indicate that both layers can grow epitaxially with an （001） texture. The antiferromagnetic-ferromagnetic transition temperature of FeRh increased from 100℃ to 200℃ by depositing the FeRh layer on a disordered or partially ordered FePt layer. When a magnetic field was applied perpendicularly to the plane, the magnetization curves of FeRh/FePt measured at room temperature were rectangular, and the coercive force could reach up to 7.4 kOe. After transiting the FeRh layer from antiferromagnetic to soft magnetic by heating, the magnetization jumped at two critical fields during the magnetization reversal process, indicating the existence of magnetic springs, and the coercive force could decrease to about half of that at room temperature. It is proposed that the shift of the antiferromagnetic-ferromagnetic transition temperature resulted from the precipitation of Pt from FePt during the A1→L10 transformation and the migration into FeRh during the disordered B2→ordered B2 transformation. This information will be useful for improving the stability of thermally assisted magnetic storage media.