Effects of interfacial oxygen diffusion on the magnetic properties and thermal stability of Pd/CoFeB/Pd/Ta heterostructure

We investigated the effects of annealing temperatures (T_A) on a Pd (5 nm)/CoFeB (10 nm)/Pd (3 nm)/Ta (10 nm) multilayer structure. The as-deposited sample showed an amorphous state with in-plane uniaxial magnetic anisotropy (UMA), resulting in low coercivity and moderate Gilbert damping constant (α) values. Increasing T_A led to crystallization, forming bcc-CoFe (110) crystals, which increased in-plane coercivity and introduced isotropic magnetic anisotropy, slightly reducing the α. The two-fold UMA persists up to 600 °C, and the thermal stability of the in-plane magnetic anisotropy remains intact even T_A = 700 °C. The T_A significantly influenced the magnetic propertiessuch as in-plane saturation magnetization (M_s//), in-plane and out-of-plane coercivities (H_c// and H_c⊥), and in-plane effective magnetic anisotropy energy density (K_eff). Above 600 °C, K_eff decreased, indicating a transition towards uniaxial perpendicular magnetic anisotropy. Interfacial oxidation and diffusion from the Ta capping layer to the Pd/CoFeB/Pd interfaces were observed, influencing chemical bonding states. Annealing at 700 °C, reduced oxygen within TaO_x through a redox reaction involving Ta crystallization, forming TaB, PdO, and BO_x states. Ferromagnetic resonance spectra analysis indicated variations in resonance field (H_r) due to local chemical environments. The α reduction, reaching a minimum at 300 °C annealing, was attributed to reduced structural disorder from inhomogeneities. Tailoring magnetic anisotropy and spin dynamic properties in Pd/CoFeB/Pd/Ta structures through T_A-controlled oxygen diffusion/oxidation highlights their potential for SOT, DMI, and magnetic skyrmion-based spintronic devices.