Study on spin injection solid state magnetic memories

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In order to develop high speed, non-volatile, and thermally stable solid-state memory, this research studied thermal writing and spin injection writing on micro-fabricated amorphous magnetic thin films.TbFe amorphous thin films having a large perpendicular magnetic anisotropy and moderate Curie temperature were micro-fabricated by using electron beam lithography technique. In this study, thermomagnetic writing was performed by flowing current pulses into the micro-fabricated TbFe narrow path under a static magnetic field of 100 Oe. The successful writing on TbFe with a lateral size of 0.5 x 0.5 μm^2 was confirmed after the application of the current pulse of 0.14 mW and 100 nsec. The critical current density for the successful writing was increased with decreasing pulse duration, and the dependence on the pulse duration was reproduced by the numerical thermal simulation.It is necessary to exhibit high tunnel magneto-resistance (TMR) ratio in TbFe based magnetic tunnel junctions to utilize the TbFe memory layer as an element of the magnetic random access memory. We, therefore, tried to fabricate magnetic tunneling junctions having the structure of TbFe (20 nm) / CoFe (tnm) / Al-0 (1.6 nm) / CoFe (t nm) / TbFe (20 nm). By inserting thin CoFe layers at t = 1 nm, large TMR ratio of 12% was confirmed. Further improvement of the TMR ratio is expected by optimizing the deposition condition and the structure of the junction.