Heusler Half-Metals on GaAs for Spin Injection

摘要

Epitaxial films of the half-metallic ferromagnets Co_2MnAl and Co_2MnGa were grown on GaAs substrates by MBE. The similar structure and close lattice matching to GaAs make them good candidates for spintronic devices. Magnetic and transport properties of the full Heusler alloys show several anomalous properties. Magnetization measurements yield ferromagnetic Curie temperatures of T_C～800-1000 K, illustrating that cobalt has a stronger exchange interaction compared to nickel-based materials, such as Ni_2MnGa, having Curie temperatures in the range T_C～300-400 K. Measurements in the Hall geometry with the field applied perpendicular to the layers exhibit a giant Hall effect (GHE) at room temperature. The GHE is a result of the extraordinary Hall effect and is driven by the strong out-of-plane magnetization. Epitaxial Co_(1-x)Mn_x films were also grown on GaAs. The range of ferromagnetism for epitaxially strained Co_(1-x)Mn_x, film is found for x_(FM) < 0.7, unlike bulk alloys where X_(FM) < 0.32.