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

The magnetic and thermal properties of Co 70.5 Fe 4.5 Si1 5 B 10 and Ni 16 Fe 62 Si 8 B 14 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 Co 90 Fe 10 and Ni 20 Fe 80 and other ternary amorphous alloys composed of Co 60 Fe 20 B 20 , and Co 24 Fe 56 B 20 . 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 70.5 Fe 4.5 Si 15 B 10 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.