AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI-TuM

Paper MI-TuM4
Co@sub 2@MnGe/Ga@sub 1-x@Al@sub x@As Heterostructures: Growth, Characterization and Spin Injection

Tuesday, November 16, 2004, 9:20 am, Room 304A

Session: Spintronics
Presenter: X.Y. Dong, University of Minnesota
Authors: X.Y. Dong, University of Minnesota
C. Adelmann, University of Minnesota
J. Strand, University of Minnesota
X. Lou, University of Minnesota
S. McKernan, University of Minnesota
J.Q. Xie, University of Minnesota
B.D. Schultz, University of Minnesota
A.K. Petford-Long, University of Oxford
P.A. Crowell, University of Minnesota
C.J. Palmström, University of Minnesota
Correspondent: Click to Email
A number of ferromagnetic Heusler alloys of the type MMnX ("half" Heusler) and M@sub 2@MnX ("full" Heusler) have been predicted to be half-metallic @super 1@. The ability to grow Co@sub 2@MnGe epitaxially on GaAs, the predicted half-metallicity and the high Curie temperature, make it an ideal candidate for a spin injecting contact. Co@sub 2@MnGe epitaxial films were grown by molecular beam epitaxy (MBE) on Ga@sub 1-x@Al@sub x@As (001) surfaces prepared in a separate MBE-growth chamber and transferred in ultra high vacuum (<10@super -10@ torr) to the Heusler alloy growth MBE chamber. In-situ RHEED, ex-situ XRD and TEM demonstrate the epitaxial single crystallinity of the films. In-plane VSM measurements showed that the Co@sub 2@MnGe films have a 1000 emu/cm@super 3@ saturation magnetization at room temperature and a 8 Oe coercivity. A SQUID magnetometer was used to measure the out of plane magnetization, which was found to saturate around 1 Tesla. In order to measure the spin injection, tunneling Schottky barrier contact spin-LED structures were fabricated from MBE-grown p-Ga@sub 0.9@Al@sub 0.1@As/GaAs(100Å)/n-Ga@sub 0.9@Al@sub 0.1@As/Co@sub 2@MnGe/Al heterostructures. The 70Å thick Co@sub 2@MnGe Schottky barrier injector was grown at 175°C and the 25Å thick Al capping layer used to prevent oxidation during exposure to air was grown at 0°C. The epitaxial heterostructures were processed into LED devices and the devices were operated with the Schottky contact under reverse bias and the p-i-n LED under forward bias. Electroluminescence was collected along the sample normal. The circular polarization of the observed electroluminescence was 14% indicating a spin injection efficiency of 14% at 2K. To our knowledge, this is the first time demonstration of spin-injection from a Heusler alloy into a semiconductor. @FootnoteText@ @footnote 1@ S. Fujii, S. Sugimura, S. Ishida, and S. Asano., J. Phys.:Condens. Matter 2, 8583 (1990).