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Spatially homogeneous ferromagnetism of (Ga, Mn)As

Abstract

Mn-doped GaAs is a ferromagnetic semiconductor1,2, widely studied because of its possible application for spin-sensitive ‘spintronics’ devices3,4. The material also attracts great interest in fundamental research regarding its evolution from a paramagnetic insulator to a ferromagnetic metal5,6. The high sensitivity of its physical properties to preparation conditions and heat treatments7,8 and the strong doping and temperature dependencies of the magnetic anisotropy9,10 have generated a view in the research community that ferromagnetism in (Ga, Mn)As may be associated with unavoidable and intrinsic strong spatial inhomogeneity. Muon spin relaxation (μSR) probes magnetism, yielding unique information about the volume fraction of regions having static magnetic order, as well as the size and distribution of the ordered moments11,12,13. By combining low-energy μSR, conductivity and a.c. and d.c. magnetization results obtained on high-quality thin-film specimens, we demonstrate here that (Ga, Mn)As shows a sharp onset of ferromagnetic order, developing homogeneously in the full volume fraction, in both insulating and metallic films. Smooth evolution of the ordered moment size across the insulator–metal phase boundary indicates strong ferromagnetic coupling between Mn moments that exists before the emergence of fully itinerant hole carriers.

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Figure 1: Magnetization and resistivity of film specimens.
Figure 2: μSR time spectra.
Figure 3: Volume fractions and internal fields.

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Acknowledgements

We acknowledge financial support from US NSF DMR-05-02706 and DMR-08-06846 (Material World Network, Inter-American Materials Collaboration Program) and DMR-0213574 (MRSEC) at Columbia; and Grant-in-Aids from MEXT/JSPS, the GCOE Program at Tohoku University, the Research and Development for Next-Generation Information Technology Program (MEXT) and NAREGI Nanoscience Project at Tohoku. This work was carried out partially at the Swiss Muon Source SμS, PSI, Villigen, Switzerland. We also thank M. Sawicki for assistance in magnetization measurements.

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Y.J.U. and E.M. proposed the present study and organized the research project with H.O. and S.M. The Low-Energy MuSR instrument at PSI was designed, tested and maintained by E.M., T.P., A.S. and G.N. Specimens of (Ga, Mn)As were made by using the MBE method at the laboratory of H.O. by D.C., Y.N., T.T., F.M. and H.O., who also obtained the results of susceptibility and resistivity of the specimens. S.R.D., T.G., J.P.C., G.N., A.S., E.M., D.C. and Y.J.U. worked on MuSR data acquisition at PSI, and S.R.D., T.G. and Y.J.U. analysed the MuSR spectra. J.O. and S.M. carried out calculation of internal field at the muon site. The main text was drafted by Y.J.U. after input from H.O., F.M. and S.M. on current models and understandings of electronic structures of (Ga, Mn)As. Supplementary Information A was drafted by G.N., B by D.C., C by S.R.D. and D by J.O. All authors subsequently contributed to revisions of the main text and Supplementary Information.

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Correspondence to Y. J. Uemura.

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Dunsiger, S., Carlo, J., Goko, T. et al. Spatially homogeneous ferromagnetism of (Ga, Mn)As. Nature Mater 9, 299–303 (2010). https://doi.org/10.1038/nmat2715

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