Spinodal decomposition to control magnetotransport in (Ge,Mn) films

I.-S. Yu, M. Jamet, T. Devillers, A. Barski, P. Bayle-Guillemaud, C. Beigné, J. Rothman, V. Baltz, and J. Cibert

Phys. Rev. B 82, 035308 – Published 16 July 2010

Abstract

Changing the morphology of the growing surface and the nature of residual impurities in (Ge,Mn) layers dramatically changes nanospinodal decomposition, i.e., the morphology of ferromagnetic Mn-rich inclusions. By this way, we are able to control the magnetotransport properties of (Ge,Mn) films. By using different substrates and substrate preparation, we have indeed obtained $p$ -type layers with nanocolumns, either parallel or entangled, and $n$ -type layers with spherical clusters. Holes exhibit an anomalous Hall effect and electrons exhibit a tunneling magnetoresistance, both with a clear dependence on the magnetization of the Mn-rich inclusions; holes exhibit orbital MR and electrons show only the normal Hall effect, and an additional component of magnetoresistance due to weak localization, all three being independent of the magnetic state of the Mn-rich inclusions. Identified mechanisms point to the position of the Fermi level of the Mn-rich material with respect to the valence band of germanium as a crucial parameter for the control and the optimization of magnetotransport in such hybrid layers.

Received 3 May 2010

DOI:https://doi.org/10.1103/PhysRevB.82.035308

Authors & Affiliations

I.-S. Yu^1,2,3, M. Jamet¹, T. Devillers¹, A. Barski¹, P. Bayle-Guillemaud¹, C. Beigné¹, J. Rothman⁴, V. Baltz⁵, and J. Cibert²

¹Institut des Nanosciences et Cryogénie, SP2M, CEA-UJF, F-38054 Grenoble, France
²Institut Néel, CNRS-UJF, BP 166, F-38042 Grenoble, France
³Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, 10617 Taiwan, Republic of China
⁴Laboratoire d’Electronique et des Technologies de l’Information, CEA, F-38054 Grenoble, France
⁵Institut des Nanosciences et Cryogénie, Spintec, CEA-CNRS-UJF-INPG, F-38054 Grenoble, France

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Vol. 82, Iss. 3 — 15 July 2010

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Images

Figure 1
TEM cross section of (Ge,Mn) films grown on Ge(001). (a) 80-nm-thick ${Ge}_{0.9} {Mn}_{0.1}$ film grown at $100 ° C$ according to the surface preparation described in Ref. 9. (b) ${Ge}_{0.94} {Mn}_{0.06}$ film grown at $100 ° C$ on the facetted Ge surface. (c) and (d) ${(GeMn / Ge)}_{4}$ superlattices grown on Ge. The Ge spacer is 5 nm thick. The Mn concentration, deposition rate, and growth temperature are 6%, $0.2 Å / s$ , and $100 ° C$ in (c) and 10%, $0.13 Å / s$ , and $140 ° C$ in (d), respectively.Reuse & Permissions
Figure 2
TEM cross section of 80-nm-thick layers grown at $100 ° C$ : (a) low magnification and (b) high magnification ${Ga-Ge}_{0.9} {Mn}_{0.1}$ film, (c) low magnification and (d) high magnification ${Ge}_{0.94} {Mn}_{0.06}$ film after depositing a 40-nm-thick Ge buffer on GaAs(001), and (e) low magnification and (f) high magnification ${As-Ge}_{0.98} {Mn}_{0.02}$ film.Reuse & Permissions
Figure 3
(Color online) Magnetic measurements performed on (a) and (b) ${Ga-Ge}_{0.9} {Mn}_{0.1}$ and (c) and (d) ${As-Ge}_{0.94} {Mn}_{0.06}$ samples, respectively. (a) Magnetization curves recorded at different temperatures. Open circles are experimental data and solid lines are fits using a Langevin function for $T = 50$ , 80, 100, and 120 K. At 200 K, nanocolumns are paramagnetic. The inset shows magnetization curves at 5 K with and without the paramagnetic contribution from diluted Mn atoms in the Ge matrix. (b) Zero field cooled–field cooled (ZFC-FC) curves at 0.015 T and magnetic remanence $M_{r}$ after maximum field cooling at 5 T. Inset: saturation magnetization at 2 T. (c) Magnetization curves recorded at 5 and 100 K showing the respective contributions from diluted Mn, Mn-rich precipitates, and ${Ge}_{3} {Mn}_{5}$ clusters. (d) ZFC-FC curves at 0.015 T and magnetic remanence $M_{r}$ after maximum field cooling at 5 T. Inset: TEM image of a ${Ge}_{3} {Mn}_{5}$ cluster.Reuse & Permissions
Figure 4
(Color online) Magnetotransport in ${Ga-Ge}_{0.9} {Mn}_{0.1}$ ; the magnetic field is applied normal to the film plane: (a) temperature dependence of the zero-field resistivity. Inset: SIMS measurements performed on two ${Ga-Ge}_{0.9} {Mn}_{0.1}$ films of different thicknesses and showing reproducible Ga outdiffusion into the (Ge,Mn) film; (b) MR (in %) up to 8 T as a function of ${(μ_{0} H)}^{2}$ and recorded at 20, 50, and 150 K. Two separate MR contributions can be identified: EMR at low magnetic field and OMR at high field. Inset: MR (in %) as a function of $μ_{0} H$ . (c) and (d) AHE (red curve) compared to magnetization (blue curve) at 2–3 and 4–5 K, respectively. Inset: AHE at 10, 100, and 150 K.Reuse & Permissions
Figure 5
(Color online) Magnetotransport in ${As-Ge}_{0.94} {Mn}_{0.06}$ . (a) Field dependence and (b) temperature dependence of the MR anisotropy, for different orientations of the field; symbols are experimental data, solid lines are calculated ones. The inset in (b) shows the SIMS profile of As atoms. (c) and (d) MR and magnetization as functions of the field applied in plane. In (d), the field sweep directions are indicated by colored arrows attached to the plots.Reuse & Permissions

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