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ABSTRACT: We report the magnetic and transport properties of two promising half metallic/GaAs hybrid spintronic structures with respect to their structural features. The Co<sub>2</sub> MnGa/GaAs(100) has shown a very low magnetic moment which is attributed to the columnar structure and the interface amorphous layer as from the HRTEM images. The out of plane hysteresis loops have shown a double switching which is related to the interface layer with different magnetic properties. In the Fe<sub>3</sub>O<sub>4</sub>/GaAs(100) system, the fast saturation of the magnetization indicates the low antiphase boundaries, which is supported by the HRTEM image. Furthermore, the moderate barrier height and the heavily damped processional response to the applied field pulses may be related to the interface structure.
IEEE Transactions on Magnetics 11/2009; · 1.36 Impact Factor
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ABSTRACT: The interfacial, electrical, and magnetic properties of the Heusler alloy Co <sub>2</sub> MnGa grown epitaxially on GaAs(100) are presented with an emphasis on the use of this metal-semiconductor combination for a device that operates on the principles of spin-injection between the two materials. Through systematic growth optimization the stoichiometry in the bulk Co <sub>2</sub> MnGa can be controlled to better than ±2%, although the interface is disordered and limits the spin-injection efficiency in a practical spintronic device irrespective of the half-metallic nature of the bulk metal. Molecular beam epitaxial growth was monitored in situ by reflection high energy electron diffraction and the bulk composition was measured ex situ with inductively coupled plasma optical emission spectroscopy. The Co <sub>2</sub> MnGa L2<sub>1</sub> cubic structure is strained below a thickness of 20 nm on GaAs(100) but relaxed in films thicker than 20 nm. Electrical measurements on the Co <sub>2</sub> MnGa reveal general characteristics of a disordered electron system with insulating behavior for layer thicknesses ≪4 nm . Thicker layers show a negative magnetoresistance with extraordinary Hall effect constants up to 30 Ω T <sup>-1</sup> . Spin polarization transfer across the interface between Co <sub>2</sub> MnGa and GaAs is approximately 6.4% at 5 K in the current of a GaAs p-i-n diode even with compositional disorder at the interface.
Journal of Applied Physics 07/2009; · 2.17 Impact Factor
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Y.B. Xu,
S. Hassan,
P. Wong,
J. Wu,
J.S. Claydon,
Y.X. Lu, C.D. Damsgaard,
J.B. Hansen,
C.S. Jacobsen,
Y. Zhai,
G. van der Laan,
R. Feidenhans,
S.N. Holmes
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ABSTRACT: Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide Fe <sub>3</sub>O <sub>4</sub> on GaAs(100) and the unit cell of the Fe<sub>3</sub>O<sub>4</sub> was found to be rotated by 45<sup>deg</sup> to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films are controlled by uniaxial magnetic anisotropy. The dynamic response of the sample shows a heavily damped precessional response to the applied field pulses. In the Heusler alloy system of Co<sub>2</sub>MnGa on GaAs, we found that the magnetic moment was reduced for thicknesses down to 10 nm, which may account for the lower than expected spin-injection efficiency from the spin-light-emitting diode structures. Using the element-specific technique of X-ray magnetic circular dichroism (XMCD), the reduced spin moments were found to originate from the Mn rather than the Co atoms, and the improvement of the interface is thus needed to increase the spin injection efficiency in this system. Further studies of the I-V characteristics of Fe<sub>3</sub>O<sub>4</sub>/GaAs(100) and Fe<sub>3</sub>O<sub>4</sub>/MgO/GaAs(100) show that the Fe<sub>3</sub> O<sub>4</sub> -based spintronic structures have a well-defined Schottky or tunneling barrier of moderate barrier height, which is encouraging for high-efficient spin injection.
IEEE Transactions on Magnetics 12/2008; · 1.36 Impact Factor
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M.C. Hickey, C.D. Damsgaard,
I. Farrer,
S.N. Holmes,
A. Husmann,
J.B. Hansen,
C.S. Jacobsen,
D.A. Ritchie,
R.F. Lee,
G.A.C. Jones,
M. Pepper,
Department of Physics, Technical University of Denmark, Lyngby,
Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge,
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ABSTRACT: Electrical spin injection in a narrow [100] In{sub 0.2}Ga{sub 0.8}As quantum well in a GaAs p-i-n optical device is reported. The quantum well is located 300 nm from an AlGaAs Schottky barrier and this system is used to compare the efficiencies and temperature dependences of spin injection from Fe and the Heusler alloy Co{sub 2.4}Mn{sub 1.6}Ga grown by molecular-beam epitaxy. At 5 K, the injected electron spin polarizations for Fe and Co{sub 2.4}Mn{sub 1.6}Ga injectors are 31% and 13%, respectively. Optical detection is carried out in the oblique Hanle geometry. A dynamic nuclear polarization effect below 10 K enhances the magnetic field seen by the injected spins in both devices. The Co{sub 2.4}Mn{sub 1.6}Ga thin films are found to have a transport spin polarization of {approx}50% by point contact Andreev reflection conductivity measurements.
Applied Physics Letters 06/2005; 86(25). · 3.84 Impact Factor
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M. C. Hickey, C. D. Damsgaard,
I. Farrer,
S. N. Holmes,
A. Husmann,
J. B. Hansen,
C. S. Jacobsen,
D. A. Ritchie,
R. F. Lee,
G. A. C. Jones,
M. Pepper
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ABSTRACT: Electrical spin injection in a narrow [100] In0.2Ga0.8As quantum well in a GaAs p‐i‐n optical device is reported. The quantum well is located 300 nm from an AlGaAs Schottky barrier and this system is used to compare the efficiencies and temperature dependences of spin injection from Fe and the Heusler alloy Co2.4Mn1.6Ga grown by molecular-beam epitaxy. At 5 K, the injected electron spin polarizations for Fe and Co2.4Mn1.6Ga injectors are 31% and 13%, respectively. Optical detection is carried out in the oblique Hanle geometry. A dynamic nuclear polarization effect below 10 K enhances the magnetic field seen by the injected spins in both devices. The Co2.4Mn1.6Ga thin films are found to have a transport spin polarization of ∼ 50% by point contact Andreev reflection conductivity measurements.
Applied Physics Letters 06/2005; 86(25):252106-252106-3. · 3.84 Impact Factor
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J. Appl. Phys. 105(2009),124502.
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Y.B. Xu,
S. Hassan,
P. Wong,
J Wu,
J.S. Claydon,
Y.X. Lu, C.D. Damsgaard,
J B Hansen,
C.S. Jacobsen,
Y. Zhai,
G van der Laan,
R. Feidenhans'l,
S.N. Holmes
IEEE Trans. Magn. 44(2008)11,2959-2965.
