Epitaxial growth of the Heusler alloy Co2Cr1−xFexAl

We report a method for the growth of single-phase epitaxial thin films of compounds from the family of Heusler alloys Co2Cr1−xFexAl. Elemental targets were dc magnetron sputtered in 1.5 mtorr Ar gas onto MgO substrates held at 500 °C at a total growth rate of ≈0.8 Å/s. As the Fe content increases, the structural quality improves, the level of chemical ordering increases, and the slope of the resistivity versus temperature, dρ/dt, above 50 K changes from negative to positive. An extraordinary Hall resistivity exceeding 1×10−8 Ω m is observed in the Cr-containing alloys at low temperature and room temperature. Preliminary work on the incorporation of a single quaternary alloy into spin valves shows maximum giant magnetoresistances ranging from 4% at 15 K to 2% at room temperature.