Interface Dzyaloshinskii-Moriya interaction in the interlayer exchange antiferromagnetic coupled Pt/CoFeB/Ru/CoFeB systems

摘要

Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchangecoupled (IEC) Pt/Co$_{20}$Fe$_{60}$B$_{20}$(1.12nm)/Ru/Co$_{20}$Fe$_{60}$B$_{20}$(1.12 nm) systems have been studiedtheoretically and experimentally. Vibrating sample magnetometer has been usedto measure their magnetization at saturation and their interlayer exchangecoupling constants. These latter are found to be of an antiferromagnetic naturefor the investigated Ru range thickness (0.5-1 nm). Their dynamic magneticproperties were studied using Brillouin light scattering (BLS) technique. TheBLS measurements reveal pronounced non-reciprocal spin waves propagation. Incontrast to the calculations for symmetrical IEC CoFeB layers, thisexperimental nonreciprocity is Ru thickness and thus coupling strengthdependent. Therefore, to explain the experimental behaviour, a theoreticalmodel based on the perpendicular interface anisotropy difference between thebottom and top CoFeB layers has been developed. We show that the Ru thicknessdependence of the spin wave non-reciprocity is well reproduced by considering aconstant iDMI and different perpendicular interfacial anisotropy fields betweenthe top and bottom CoFeB layers. This anisotropy difference has been confirmedby the investigation of the CoFeB thickness dependence of effectivemagnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linearbehaviour has been observed.