S. J. Potashnik

Highly enhanced Curie temperature in low-temperature annealed [Ga,Mn]As epilayers

We report Curie temperatures up to 150 K in annealed Ga1−xMnxAs epilayers grown with a relatively low As:Ga beam equivalent pressure ratio. A variety of measurements (magnetization, Hall effect, magnetic circular dichroism and Raman scattering) suggest that the higher Curie temperature results from an enhanced free hole density. The data also indicate that, in addition to the carrier concentration, the sample thickness limits the maximum attainable Curie temperature in this material, suggesting that the free surface of Ga1−xMnxAs epilayers may be important in determining their physical properties.

Effects of annealing time on defect-controlled ferromagnetism in Ga1−xMnxAs

We have studied the evolution of the magnetic, electronic, and structural properties of annealed epilayers of Ga1−xMnxAs grown by low temperature molecular beam epitaxy. Annealing at the optimal temperature of 250 °C for less than 2 h significantly enhances the conductivity and ferromagnetism, but continuing the annealing for longer times suppresses both. These data indicate that such annealing induces the defects in Ga1−xMnxAs to evolve through at least two different processes, and they point to a complex interplay between the different defects and ferromagnetism in this material.

Above-room-temperature ferromagnetism in GaSb/Mn digital alloys

Digital alloys of GaSb/Mn have been fabricated by molecular-beam epitaxy. Transmission electron micrographs showed good crystal quality with individual Mn-containing layers well resolved, no evidence of three-dimensional MnSb precipitates was seen in as-grown samples. All samples studied exhibited ferromagnetism with temperature-dependent hysteresis loops in the magnetization accompanied by metallic p-type conductivity with a strong anomalous Hall effect (AHE) up to 400 K (limited by the experimental setup). The anomalous Hall effect shows hysteresis loops at low temperatures and above room temperature very similar to those seen in the magnetization. The strong AHE with hysteresis indicates that the holes interact with the Mn spins above room temperature. All samples are metallic, which is important for spintronics applications.

Spin-polarized tunneling in hybrid metal-semiconductor magnetic tunnel junctions

We demonstrate efficient spin-polarized tunneling between a ferromagnetic metal and a ferromagnetic semiconductor with highly mismatched conductivities. This is indicated by a large tunneling magnetoresistance (up to 30%) at low temperatures in epitaxial magnetic tunnel junctions composed of a ferromagnetic metal (MnAs) and a ferromagnetic semiconductor

Capping-induced suppression of annealing effects on Ga1−xMnxAs epilayers

({\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As})

Hybrid ferromagnetic/semiconductor heterostructures for spintronics

separated by a nonmagnetic semiconductor (AlAs). Analysis of the current-voltage characteristics yields detailed information about the asymmetric tunnel barrier. The low temperature conductance-voltage characteristics show a zero bias anomaly and a

Coercive field and magnetization deficit in Ga1−xMnxAs epilayers

\sqrt{V}

Novel ferromagnetism in digital GaAs/Mn and GaSb/Mn alloys

dependence of the conductance, suggesting a correlation gap in the density of states of

External control of the direction of magnetization in ferromagnetic InMnAs/GaSb heterostructures

{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}.

Magneto-optic effects in spin-injection devices

These experiments suggest that MnAs/AlAs heterostructures offer well characterized tunnel junctions for high efficiency spin injection into GaAs.