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Synthesis and characterization of high quality ferromagnetic Cr-doped GaN and AlN thin films with Curie temperatures above 900K

Published online by Cambridge University Press:  01 February 2011

Stephen Y. Wu ,
H. X. Liu ,
Lin Gu ,
R. K. Singh ,
M. van Schilfgaarde ,
David J. Smith ,
N. R. Dilley ,
L. Montes ,
M. B. Simmonds  and
N. Newman
Stephen Y. Wu
Affiliation:
Dept. of Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287–6006
H. X. Liu
Affiliation:
Dept. of Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287–6006
Lin Gu
Affiliation:
Center for Solid State Science, Arizona State University, Tempe, AZ 85287
R. K. Singh
Affiliation:
Dept. of Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287–6006
M. van Schilfgaarde
Affiliation:
Dept. of Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287–6006
David J. Smith
Affiliation:
Center for Solid State Science, Arizona State University, Tempe, AZ 85287 Dept. of Physics and Astronomy, Arizona State University, Tempe, AZ 85287–1504
N. R. Dilley
Affiliation:
Quantum Design, San Diego, CA 92121
L. Montes
Affiliation:
Quantum Design, San Diego, CA 92121
M. B. Simmonds
Affiliation:
Quantum Design, San Diego, CA 92121
N. Newman
Affiliation:
Dept. of Chemical and Materials Engineering, Arizona State University, Tempe, AZ 85287–6006
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Abstract

Reactive MBE growth was used to synthesize ferromagnetic Cr-doped GaN and AlN thin films with Curie temperatures above 900K. 2% Cr-doped GaN and 7% Cr-doped AlN were found to have a saturation magnetization moment of 0.42 and 0.6 μB/Cr atom, indicating that ∼14% and ∼20% of the Cr, respectively, are magnetically active. Structural characterization using X-ray diffraction (XRD) and transmission electron microscopy (TEM) did not find evidence of a ferromagnetic secondary phase. Electrical characterization indicate that the resistivity of the Cr-doped GaN films depends exponentially on temperature as R=Roexp[(To/T)1/2], characteristic of variable range hopping. In contrast, Cr-doped AlN films are highly resistive. Local spin density functional calculations predict that Cr forms a deep level defect in both systems and the t2 level falls approximately at midgap. Our theoretical and experimental results indicate that ferromagnetism in Cr-doped GaN and AlN arises as a result of the double exchange mechanism within the partially filled Cr t2 band.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 798: Symposium Y – GaN and Related Alloys , 2003 , Y10.57
Copyright
Copyright © Materials Research Society 2004

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References

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