C. J. Palmstrøm

Electrical detection of spin transport in lateral ferromagnet–semiconductor devices

The development of semiconductor spintronics requires a reliable electronic means for writing, processing and reading information using spin-polarized carriers. Here, we demonstrate a fully electrical scheme for achieving spin injection, transport and detection in a single device. Our device consists of a lateral semiconducting channel with two ferromagnetic contacts, one of which serves as a source of spin-polarized electrons and the other as a detector. Spin detection in the device is achieved through a non-local, spin-sensitive, Schottky-tunnel-barrier contact whose electrochemical potential depends on the relative magnetizations of the source and detector. We verify the effectiveness of this approach by showing that a transverse magnetic field suppresses the non-local signal at the detection contact by inducing spin precession and dephasing in the channel (the Hanle effect). The sign of the signal varies with the injection current and is correlated with the spin polarization in the channel as determined by optical Kerr rotation measurements.

Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface

We show that the accumulation of spin-polarized electrons at a forward-biased Schottky tunnel barrier between Fe and -GaAs can be detected electrically. The spin accumulation leads to an additional voltage drop across the barrier that is suppressed by a small transverse magnetic field, which depolarizes the spins in the semiconductor. The dependence of the electrical accumulation signal on magnetic field, bias current, and temperature is in good agreement with the predictions of a drift-diffusion model for spin-polarized transport.

SELF-ASSEMBLED ERAS ISLANDS IN GAAS: GROWTH AND SUBPICOSECOND CARRIER DYNAMICS

We report the growth of self-assembled ErAs islands embedded in GaAs by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. X-ray diffraction shows superlattice fringes from such samples. Pump–probe measurements indicate carrier capture times as short as 120 fs. These capture times are strongly correlated with the period of the superlattice.

Spin injection from the Heusler alloy Co2MnGe into Al0.1Ga0.9As∕GaAs heterostructures

Electrical spin injection from the Heusler alloy Co2MnGe into a p-i-nAl0.1Ga0.9As∕GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co2MnGe decays more rapidly with increasing temperature.

Shape memory and ferromagnetic shape memory effects in single-crystal Ni2mnGa thin films

Epitaxial Ni2MnGa and Ni2Mn1.2Ga0.8 thin films have been grown by molecular beam epitaxy on GaAs (001) substrates with Sc0.3Er0.7As interlayers. Structural characterization of as-grown films confirms the epitaxially stabilized single crystal structure of the films and indicates that the films grow pseudomorphically on GaAs (001) substrates in a tetragonal structure (a=b=5.65 A, c=6.18 A). The films are ferromagnetic at room temperature with coercivity of ∼50 Oe, saturation magnetization of ∼250 emu/cm3, and weak in-plane magnetic anisotropy. The Curie temperature of the films is found to be ∼340 K. However, while the films were attached to the substrate martensitic phase transformations were not observed. In order to observe martensitic phase transformations, free-standing Ni2MnGa bridges and cantilevers were fabricated using front and back side photolithography together with a combination of dry and wet etching. After removal of the substrate, the free-standing bridges and cantilevers showed a unique tem...

Spin Injection and Relaxation in Ferromagnet-Semiconductor Heterostructures

We present a detailed description of spin injection and detection in

Anomalous magnetotransport properties of epitaxial full Heusler alloys

\mathrm{Fe}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}∕\mathrm{GaAs}

Dynamic nuclear polarization by electrical spin injection in ferromagnet-semiconductor heterostructures.

heterostructures for temperatures from 2 to 295 K. Measurements of the steady-state spin polarization in the semiconductor indicate three temperature regimes for spin transport and relaxation. At temperatures below 70 K, spin-polarized electrons injected into quantum well structures form excitons, and the spin polarization in the quantum well depends strongly on the electrical bias conditions. At intermediate temperatures, the spin polarization is determined primarily by the spin-relaxation rate for free electrons in the quantum well. This process is slow relative to the excitonic spin-relaxation rate at lower temperatures and is responsible for a broad maximum in the spin polarization between 100 and 200 K. The spin injection efficiency of the

Exchange biasing of the ferromagnetic semiconductor Ga1−xMnxAs

\mathrm{Fe}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}

Epitaxial growth of ferromagnetic Ni2MnIn on (001) InAs

Schottky barrier decreases at higher temperatures, although a steady-state spin polarization of at least 6% is observed at 295 K.