Correlations between Structural and Magnetic Properties of Co2FeSi Heusler-Alloy Thin Films

The structural and magnetic properties are the most important parameters for practical applications of Co-based Heusler alloys. The correlations between the crystallization degree, chemical order, magnetic coercivity, saturation magnetization (MS), and in-plane magnetic anisotropies are systematically investigated for Co2FeSi (CFS) films fabricated at different temperatures (TS). XRD shows that the CFS layer changes progressively from a disordered crystal structure into a chemically disordered A2 structure and further into a chemically ordered B2 and even L21 structures when increasing TS up to 480 °C. Meanwhile, the static angular remanence magnetization curves show a clear transition of magnetic anisotropy from twofold to fourfold symmetry, due to the competition effect between the uniaxial anisotropy field HU and biaxial anisotropy field HB. The HU value is found to be weakly dependent on TS, while HB shows a continuous enhancement at TS>300 °C, implying that the enhancement of the L21 ordering degree would not weaken the biaxial anisotropy. The varying trend of HB is similar to MS, which can be respectively attributed to the improved crystal structure and chemical order. The anisotropic fields and their variation behaviors determined by a vibrating sample magnetometer are highly consistent with the results by a time-resolved magneto-optical Kerr effect study. Our findings provide a better understanding of the structural ordering and magnetic anisotropy, which will be helpful for designing advanced spintronic devices.