AVS 49th International Symposium
    Magnetic Interfaces and Nanostructures Monday Sessions
       Session MI+EL-MoM

Paper MI+EL-MoM3
Spin Dependent Electron Transport in Hybrid Ferromagnet/GaAs Structures at Room Temperature

Monday, November 4, 2002, 9:00 am, Room C-205

Session: Spintronic Materials and Hybrid Devices
Presenter: J.A.C. Bland, University of Cambridge, UK
Authors: S.J. Steinmuller, University of Cambridge, UK
W.S. Cho, University of Cambridge, UK
A. Hirohata, University of Cambridge, UK
C.M. Guertler, University of Cambridge, UK
G. Wastlbauer, University of Cambridge, UK
T. Taniyama, University of Cambridge, UK
J.A.C. Bland, University of Cambridge, UK
Correspondent: Click to Email
We report on the investigation of room temperature (RT) spin dependent electron transport in ferromagnet(FM)/GaAs hybrid Schottky barrier structures by photoexcitation. Spin accumulation in the GaAs was achieved by optical pumping with circularly polarised light. The photon helicity and the applied magnetic field were both introduced perpendicular to the plane of the film. Various FM materials were used (NiFe, Fe and Co) and investigated at different thicknesses (t=2.5nm, 5.0nm and 7.5nm). Furthermore an antiferromagnetic Cr sample was prepared as a reference. We measured the helicity-dependent photocurrent (PC), that is the difference in PC for illumination with right (i@super +@) and left circularly polarised light (i@super -@), for applied magnetic fields in the range from -2 T to 2 T as well as the spin polarisation P=(i@super +@ - i@super -@)/(i@super +@ + i@super -@) of PC. NiFe and Fe showed a rather strong effect (P in the range 0.2-2%) increasing with film thickness, whereas almost no effect was observed in the Co. The magnetic field dependence of the helicity-dependent PC was in good agreement with polar MOKE measurements, proving that magnetic effects in the GaAs are negligible at RT. No field dependent effect was seen for the Cr as expected. Moreover we carried out measurements at different doping densities of the GaAs substrate (n- and p-type), showing the importance of the Schottky barrier in our experiment, and different photon energies. We also discuss the results of similar measurements on NiFe/Cu/Co spin valve structures. We show that our combined data provides strong support for our model of electron spin filtering at RT based on tunnelling of spin polarised electrons across the Schottky barrier followed by ballistic transport in the FM.