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

Abstract

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 (Ga 1−x Mn x As) separated by a nonmagnetic semiconductor (AlAs). Analysis of the current-voltage characteristics yields detailed information about the asymmetric tunnel barrier. The low temperature conductancevoltage characteristics show a zero bias anomaly and a √ V dependence of the conductance, indicating a correlation gap in the density of states of Ga 1−x Mn x As. These experiments suggest that MnAs/AlAs heterostructures offer well characterized tunnel junctions for high efficiency spin injection into GaAs.

Vertical spin transport in MnAs/GaMnAs heterostructures

“…1(b) help in figuring out the shape of this composite tunnel barrier. We observe a similar asymmetry in the conductivity curves as those of single-barrier hybrid MTJs [5]. The difference is that DTJs are more conducting under the reverse bias, which implies that the barrier height experienced by MnAs is larger than that experienced by GaMnAs (we define forward bias when the potential of MnAs is higher than that of GaMnAs).…”

“…However, a definite evidence of metal-semiconductor spin injection probed by electrical measurement is still lacking. A partial success was accomplished by one of the authors in MnAs/GaMnAs hybrid magnetic tunnel junctions (MTJs) separated by AlAs tunnel barriers [5]. GaMnAs is the most studied ferromagnetic semiconductor [6], and MnAs is a metallic ferromagnet that can be grown epitaxially on the top of zinc-blende semiconductors by low-temperature molecular beam epitaxy (MBE) [7].…”

Spintronics: Fundamentals and applications

“…Despite its simplicity, the Julliè re model for the tunneling magnetoresistance has continued to be used for interpreting the spin polarization in various MTJ's. Recent examples include F regions made of manganite perovskites displaying colossal magnetoresistance (CMR; Bowen et al, 2003), suggesting P N Ͼ0.95; magnetite (Fe 3 O 4 ; Hu and Suzuki, 2002), with PϽ0 and TMR Ͻ0; III-V ferromagnetic semiconductors (Chun et al, 2002); a nonmagnetic semiconductor used as a tunneling barrier (Kreuzer et al, 2002); Co/carbon nanotube/Co MTJ (Tsukagoshi et al, 1999); and resonant tunneling in F/I/N/F junctions (Yuasa et al, 2002).…”

“…These included CdMnTe (Oestreich et al, 1999), BeMnZnSe (Fiederling et al, 1999), and ZnMnSe . In the second approach ferromagnetic semiconductors like (Ga,Mn)As (Ohno, Young, et al, 1999;Chun et al, 2002;Mattana et al, 2003) were used. Both approaches were also employed to inject spins into CdSe/ZnSe (Seufert et al, 2004) and InAs (Chye et al, 2002) quantum dots, respectively.…”

Ferromagnetism in ZnTe:Cr film grown on Si(1 0 0)

“…The primary issue for a material to act as source of spin current injection/magnetic storage layer is that it must be ferromagnetic well above room temperature and the prepared film must exhibit good crystallinity without any secondary phase [1][2][3][4]. Nowadays, a large number of attempts have been made to see ferromagnetic properties in different semiconductor hosts by doping with transition metal impurities.…”