Magnetic properties of single-layer and trilayer structured CoFeB based magnetic thin films
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The new field of research termed as spintronics is in multidisciplinary domain and its success relies on a strong synergy between breakthroughs in basic science and industrial applications. With the recent advances in the development of various spintronics devices, it is very much essential to study the magnetic properties of those materials (metallic alloy thin films) that are commonly used in such applications. Among various magnetic thin films, CoFeB based thin films have been found to be one of the promising materials suitable for various spintronics applications in modern magneto-electronic devices due to their tunable magnetic properties. In this context, a systematic investigation has been carried out in this thesis work on the effects of thickness, composition and temperature on the structural and magnetic properties of single-layer amorphous Co80-yFeyB20 (t nm) thin films with two different compositions [Co40Fe40B20 (CoFeB442) and Co20Fe60B20 (CoFeB262)] over a wide range of thicknesses (7 − 200 nm). All films were prepared on thermally oxidized Si substrates at ambient temperature by DC magnetron sputtering. Structural studies confirm the presence of amorphous structure in the as-deposited films. CoFeB films with t ≤ 20 exhibit soft magnetic nature due to in-plane magnetization with uniaxial anisotropy, while for films with t > 50 nm, the soft magnetic properties are degraded due to transition of in-plane magnetization to dense stripe domain, which is induced by the increased effective magnetic anisotropy (Keff) caused by stress accumulated during the deposition process. Temperature dependent Keff showed a strong compositional dependent variation. High thermal stability of CoFeB films for both compositions was also evident from high temperature magnetization measurement.
Supervisor: Perumal Alagarsamy