Anomalous Hall effects in Co_(2)FeSi Heusler compound films and Co_(2)FeSi-Al_(2)O_(3) granular films

摘要

We fabricated three Co_(2)FeSi Heusler compound films at different temperatures (room temperature, 673, and 873 K) by rf sputtering deposition method and a series of (Co_(2)FeSi)_(x)(Al_(2)O_(3))_(1-x) (0.4 approx.< 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 Co_(2)FeSi 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 L2_(1) and B2 structures are present in the film deposited at 873 K. For the Co_(2)FeSi films deposited at 673 and 873 K, the saturated anomalous Hall resistivity (rho)_(A)~(s) scales with the longitudinal resistivity (rho)_(xx) as (rho)_(A)~(s) propor. to (rho)_(xx)~(n), with n much larger than 2. There is no scaling relation between (rho)_(A)~(s) and (rho)_(xx) for the (Co_(2)FeSi)_(x)(Al_(2)O_(3))_(1-x) (0.58 <= x <= 1, x velence 1 represents the Co_(2)FeSi film deposited at room temperature) granular films. For the granular films, as x decreases from 1 to 0.67, the magnitude of (rho)_(xx) increases by a factor of approx25, whereas the magnitude enhancement in (rho)_(A)~(s) is less than 50percent, which strongly suggests that the longitudinal and anomalous Hall transports in ferromagnetic granular films are governed by different mechanisms. The low-field Hall sensitivities of (Co_(2)FeSi)_(x)(Al_(2)O_(3))_(1-x) films with x values of 0.6 and 0.65 are large and temperature insensitivity from 300 down to approx75 K, which might make them be good candidate materials for low-field Hall sensors.