Tunnel magnetoresistance and current-induced magnetization switching in mesoscale (Ga,Mn)As magnetic tunnel junctions

ORAL

Abstract

We report measurements of the tunneling magnetoresistance (TMR) and current-induced magnetization switching in exchange-biased (Ga,Mn)As/GaAs/(Ga,Mn)As magnetic tunnel junctions (MTJs) with dimensions in the mesoscale regime ($2 - 10 \mu {\rm{m}}^2$). We observe thermally activated quenching of the TMR over two decades in temperature (0.35 K$ < T < $40 K), characterized by a functional form: $\rm{TMR}(T) = \rm{TMR}(0) [1 - \exp(-T_0/T)]$, with $T_0 \sim 10$ K. This behavior is interpreted using a model in which tunneling is dominated by the hole state bound to a Mn spin in the depletion region near the (Ga,Mn)As/GaAs interface. For $T < T_0$, such spins have a preferred orientation relative to the ``bulk'' ferromagnetic region, but at higher temperatures they become decoupled from the latter. We also discuss experiments that probe current-induced magnetization switching in these mesoscale devices. We find that in addition to complete switching between high- and low-resistance states of a MTJ, current pulses can lead to stable, intermediate resistance states, possibly due to fragmentation into multiple magnetic domains by heating. Supported by ONR-MURI.

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Authors

  • M.J. Wilson

    • Dept. of Physics, Penn State University, University Park.
    • Dept. of Physics, Penn State University, University Park PA 16802

  • P. Mitra

    • Dept. of Physics, Penn State University, University Park.

  • M. Zhu

    • Dept. of Physics, Penn State University, University Park.

  • P. Schiffer

    • Dept. of Physics, Penn State University, University Park.

  • Nitin Samarth

    • Dept. of Physics, Penn State University, University Park PA 16802
    • Center for Nanoscale Science and Materials Research Institute, Penn State University, University Park PA 16802
    • Dept. of Physics, Penn State University, University Park.
    • Materials Research Institute, Penn State University, University Park, Pennsylvania 16802
    • The Pennsylvania State University

  • L. Xue

    • Dept. of Physics, Cornell University, Ithaca.

  • K.V. Thadani

    • Dept. of Physics, Cornell University, Ithaca.

  • D.C. Ralph

    • Dept. of Physics, Cornell University, Ithaca.

  • M.E. Flatte

    • Dept. of Physics, University of Iowa, Iowa City.