Electrical Measurement of the Spin Polarization of (Ga,Mn)As
Abstract
(Ga,Mn)As is one of the most thoroughly characterized diluted magnetic semiconductors. Its spin polarization has been predicted to be close to 100% [1] and all-semiconductor magnetic tunnel junctions based on it have exhibited large magnetoresistance [2], indicating a high value of spin polarization. We have performed a direct electrical measurement of its spin polarization using Andreev reflection spectroscopy. Ga_0.95Mn_0.05As was grown with low temperature MBE on a heavily doped GaAs substrate and a top superconducting layer was deposited in situ to preserve a clean interface. Junctions with a Ga top layer exhibited conductance spectra reminiscent of a clean metallic contact between a superconductor and a ferromagnet with high spin polarization. Although the conductance spectra cannot be fit straightforwardly to the BTK theory, the large gap edge (1.4 meV) and low zero-bias conductance (G(0)), together with a suppression of G(0) below GN that persists at temperatures well above the Tc for bulk crystalline Ga (1.1K), suggest a distribution of Tc and energy gap in the Ga film. Fits, taking into account this distribution, consistently yield a spin polarization value greater than 85Ga_0.95Mn_0.05As. The measured spin polarization depends sensitively on interface quality as evidenced in the study of various samples fabricated throughout this work. [1] M. Jain et al., Phys. Rev. B 64, 245205 (2001); T. Dietl et al., Phys. Rev. B 63, 195205 (2001). [2] M. Tanaka and Y. Higo, Phys. Rev. Lett. 87, 026602 (2001). *Work done in collaboration with J.G. Braden, J.S. Parker, S.H. Chun, and N. Samarth, and supported by DARPA SPINS program.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARD26007X