Quantitative analysis of anisotropic magnetoresistance in Co₂MnZ and Co₂FeZ epitaxial thin films: A facile way to investigate spin-polarization in half-metallic Heusler compounds

Anisotropic magnetoresistance (AMR) effect has been systematically investigated in various Heusler compounds Co₂MnZ and Co ₂FeZ (Z=Al, Si, Ge, and Ga) epitaxial films and quantitatively summarized against the total valence electron number N_V. It was found that the sign of AMR ratio is negative when N_V is between 28.2 and 30.3, and turns positive when N_V becomes below 28.2 and above 30.3, indicating that the Fermi level (E_F) overlaps with the valence or conduction band edges of half-metallic gap at N_V ∼28.2 or 30.3, respectively. We also find out that the magnitude of negative AMR ratio gradually increases with shifting of E_F away from the gap edges, and there is a clear positive correlation between the magnitude of negative AMR ratio and magnetoresistive output of the giant magnetoresistive devices using the Heusler compounds. This indicates that AMR can be used as a facile way to optimize a composition of half-metallic Heusler compounds having a high spin-polarization at room temperature.