Anomalous Hall effects in Co2FeSi Heusler compound films and Co2FeSi-Al2O3 granular films

摘要

We fabricated three Co₂FeSi Heusler compound films at different temperatures (room temperature, 673, and 873 K) by rf sputtering deposition method and a series of (Co₂FeSi)_x(Al₂O₃)_1-x (0.4~x≤1) granular films at room temperature by co-sputtering method. The structures as well as the temperature behaviors of anomalous Hall resistivities, low-field Hall sensitivities, and longitudinal resistivities of those films were investigated experimentally. We found that the Co₂FeSi Heusler compound film deposited at room temperature is poorly crystallized, the film deposited at 673 K is crystallized in the disordered A2 type structure, and L2₁ and B2 structures are present in the film deposited at 873 K. For the Co₂FeSi films deposited at 673 and 873 K, the saturated anomalous Hall resistivity ρ_As scales with the longitudinal resistivity ρ_xx as ρ_As∝ρ_xxn, with n much larger than 2. There is no scaling relation between ρ_As and ρ_xx for the (Co₂FeSi)_x(Al₂O₃)_1-x (0.58≤x≤1, x=1 represents the Co₂FeSi film deposited at room temperature) granular films. For the granular films, as x decreases from 1 to 0.67, the magnitude of ρ_xx increases by a factor of ∼25, whereas the magnitude enhancement in ρ_As is less than 50%, which strongly s- ggests that the longitudinal and anomalous Hall transports in ferromagnetic granular films are governed by different mechanisms. The low-field Hall sensitivities of (Co₂FeSi)_x(Al₂O₃)_1-x films with x values of 0.6 and 0.65 are large and temperature insensitivity from 300 down to ∼75 K, which might make them be good candidate materials for low-field Hall sensors.