Enhancement in Interfacial Dzyaloshinskii-Moriya Interaction in Pt/CoFe(B)/MgO Structures by Suppression of FePt Interface Phases with the Addition of Boron

CoFeB is a versatile material used in various spintronics devices including magnetic random access memories, logic devices, and skyrmion-based devices. However, the interfacial Dzyaloshinskii-Moriya interaction energy density (D) values of CoFeB-based systems are lower than those of other ferromagnetic (FM) materials without glass formers. Therefore, strategies are necessary for enhancing D in CoFeB-based systems for skyrmion-based devices, which require adequate D to form Neel-type skyrmions. In this study, we investigate the trends of D by adjusting the boron content in the Pt/(Co10Fe90)(100-x)B-x/MgO structure. The crystalline CoFe sample (boron 0%) exhibits the lowest D among all samples, at a value even lower than those of the amorphous CoFeB samples (12-20%); this phenomenon is contrary to the anticipated relationship between the strength of D and the crystallinity of FM. Moreover, adding 4% boron leads to a 3-fold increase in D. Our microstructure analysis reveals a correlation between D and the intermixed FePt phase between the Pt and CoFe(B) layers. Furthermore, we interpret the impact of the FePt phase on D based on the work function difference between the FePt and CoFe(B) layers, which is related to the degree of spin-orbit scattering.