Thermal effect on structure and magnetic properties in CoFeAlSi alloy films

• Amorphous CoFeAlSi alloy films are fabricated by sputtering at room temperature.
• Magnetic anisotropy consists of uniaxial and cubic structural anisotropy sharing parallel easy axes.
• Oxidation arising from high temperature annealing leads to the reduction in saturation magnetization.
• The interplay between thermal dependent magnetization and crystallization behavior is demonstrated.
• The activation barrier is optically determined to be 1.32 eV.

CoFeAlSi alloy films are sputtered at room temperature and annealed at various temperatures. X-ray diffraction measurements reveal as-deposited films are amorphous and a nanocrystalline structure is formed after annealing. The coercivity is found to rapidly increase with the annealing temperature, in line with the grown nanocrystalline grain size. The angle dependent magnetic measurements reveal a thermal-induced cubic structural anisotropy develops with the annealing temperature and is superimposed on a growth-induced uniaxial anisotropy with parallel easy axes. Magnetic properties of the alloy are shown to be strongly influenced by the structural change induced by the thermal treatment. The interplay between thermal dependent magnetization and crystallization behavior of the alloy film is revealed by thermomagnetic measurements. A activation barrier of 1.32 eV is determined using the optical reflectance measurements with variable heating rates.

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