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

Abstract

The magnetic and thermal properties of Co70.5Fe4.5Si15B10 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 Delta T-x (defined as T-x - T-g). Compared with the other alloys, the amorphous Co70.5Fe4.5Si15B10 alloy exhibits low M., and low saturated field (H.). This alloy also shows estimated high T-g, large Delta T-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.