Ta Interfaced CoFeB: Role of CoFeB Thickness and Thermal Annealing in Modification of Structural and Magnetic Properties

CoFeB interfaced with heavy metals is a potential system for spintronic applications. In the present work, evolution of magnetic and structural properties of CoFeB interfaced with Ta have been studied as function of increasing thickness of magnetic film and increasing annealing temperature. While the evolution of structural properties was investigated using X-ray scattering measurements i.e., X-ray reflectivity (XRR) and grazing incidence X-ray Diffraction (GIXRD), the modification of magnetic properties were studied using vibrating sample magnetometer (VSM) and magneto-optical Kerr effect (MOKE) measurements. The detailed XRR analysis shows the diffusion of Boron to the bottom Ta layer with annealing, which increases significantly for post-crystallized phase. Such enriched B diffusion also increases the thickness of interfacial magnetic dead layer as confirmed from VSM results. The synchrotron XRD show an increased in-plane CoFe grain size relative to out-of-plane grain size, while CoFeB is interfaced with Ta. MOKE measurements confirm the presence of stress-induced uniaxial magnetic anisotropy in as-deposited CoFeB films, which reduces for Ta-interfaced CoFeB. Vacuum annealing well above the crystallization temperature eliminates such magnetic anisotropy with concurrent increase of magnetic coercivity (Hc) because of increasing grain size. CoFeB interfaced with Ta shows an abrupt enhancement of Hc, as compared to CoFeB without Ta interface.