Designing the Composition of Amorphous Free Layer of a Magnetic Tunnel Junction

The magnetic and thermal properties of Co_70.5Fe_4.5Si1₅B₁₀ and Ni₁₆Fe₆₂Si₈B₁₄ quaternary amorphous alloys (metallic glasses) used for a free layer in the magnetic tunnel junctions (MTJs) were studied to correlate magnetic and glass characterization of amorphous alloys and the performance of the MTJs with amorphous free layer. The characteristics of these amorphous free layers were compared with crystalline free layers composed of Co₉₀Fe₁₀ and Ni₂₀Fe₈₀ and other ternary amorphous alloys composed of Co₆₀Fe₂₀B₂₀, and Co₂₄Fe₅₆B₂₀. Results based on X-ray diffraction, vibrating sample magnetometer (VSM), and differential scanning calorimetry (DSC) were presented. The amorphous alloys exhibit the soft magnetic properties of low saturated magnetization (M_s) and low coercivity (H_c) in hyeteresis loops. The thermal properties were represented by the values of glass transition temperature (T_g), curie temperature (T_c), crystallization temperature (T_x), melting temperature (T_m), T_rg (defined as T_g/T_m), and DeltaT_x (defined as T_x-T_g ). Compared with the other alloys, the amorphous Co_70.5Fe_4.5Si₁₅B₁₀ alloy exhibits low M_s, and low saturated field (H_s). This alloy also shows estimated high T_g, large DeltaT_x, and high T_rg. Correlations between magnetic and glass characterization of amorphous free layer and the properties of MTJs composed of amorphous free layer were discussed.