Synthesis and Characterization, Thermal Stability and Magnetic Properties of Metallic Glass Free Layer of Magnetic Tunnel Junctions

Ferromagnetic CoFeSiB and NiFeSiB metallic glasses were produced to study the thermal and magnetic properties of glassy alloys which show the good performance for free layers in the Magnetic tunnel junctions (MTJs). The characters of amorphous materials are compared with crystalline materials composed of CoFe and NiFe. X-ray diffraction pattern was used to confirm the amorphous and crystalline state of melt-spun ribbons. The thermal stability and crystallization processes were investigated by differential scanning calorimeter (DSC). The thermal properties of amorphous alloys represent by the parameters; glass transition temperature (>580 deg. K), crystallization temperature (<830 deg. K), the large supercooled liquid region (ΔT = Tx-Tg), the reduced glass transition temperature (Trg = Tg/Tm). The alloys exhibit the soft magnet properties of high saturated magnetization (Ms), low coercive force (Hc) and high effective permeability (μe) represented to the hyeteresis loops. The magnetic characters for all alloys are measured by vibrating sample magnetometer (VSM). Amorphous ferromagnetic free layers in MTJs have a lower Ms and a higher anisotropy constant than crystalline layers. The experimental results explain how the metallic glass for free layer performs better than crystal. The good combination of thermal and magnetic properties in the amorphous material indicates the possibility of application as the glassy magnetic material.