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Ferromagnetic and structural properties of Ge1-xMnxTe epitaxial layers

Knoff W, Dziawa P, Osinniy V, Taliashvili B, Domuchowski W, Diduszko R, Domagała J, Łusakowska E, Jakieła R, Story T

Materials Science Poland

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2008

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Vol. 26, No. 4

295--300

EN

Magnetic properties of thin layers of p-Ge1–xMnxTe (x < 0.2) semimagnetic (diluted magnetic) semiconductor exhibiting carrier induced ferromagnetism were experimentally studied. The layers were grown on BaF2 (111) substrates by molecular beam epitaxy technique. X-ray diffraction analysis performed at room temperature revealed monocrystalline (111)-oriented rhombohedral (exhibiting ferroelectric properties) crystal structure of Ge1–xMnxTe layers in the entire range of Mn content studied. The examination of the magnetic properties of the layers carried out by superconducting SQUID magnetometry and ferromagnetic resonance technique showed the ferromagnetic transition with the Curie temperature in the range 10–100 K depending on the Mn content and the hole concentration. Contrary to polycrystalline GeMnTe layers, it was experimentally found that in monocrystalline layers of GeMnTe an easy magnetization axis is directed along a normal to the layer plane. This effect is discussed in terms of strain present in these layers due to thermal expansion coefficients mismatch between the substrate and the GeMnTe layer.

2

Photoemission study of Eu 2+/3+ ions in ferromagnetic (Eu,Gd)Te semiconductor layers

Dziawa P., Orłowski B. A., Osinniy V., Pietrzyk M., Taliashvili B., Story T., Johnson R. L.

Materials Science Poland

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2007

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Vol. 25, No. 2

377--382

EN

(Eu,Gd)Te ferromagnetic semiconductor layers grown by molecular beam epitaxy technique on BaF2 (111) monocrystalline substrates were investigated by resonant photoemission spectroscopy using synchrotron radiation. In n-(Eu,Gd)Te layers, a ferromagnetic transition induced by electron concentration is observed. Magnetic as well as electrical properties of this material depend strongly on the charge state (2+ vs. 3+) of Eu and Gd ions known to be sensitive to crystal stoichiometry and formation of oxide complexes. The relative concentration of Eu2+ and Eu3+ ions was determined from the analysis of the resonant photoemission energy distribution curves (EDC), measured at photon energies close to 4d-4f resonance. After various in-situ annealing and Ar sputtering procedures, a clear improvement of crystal stoichiometry of (Eu,Gd)Te layers was observed as manifested by the increase of Eu2+ intensity in the spectra. Contribution of Eu 4f shell to the total density of states was also analyzed and found at the valence band edge for Eu2+ ions and about 6 eV lower for Eu3+ ions.

3

Ferromagnetic transition in Ge1-xMnxTe semiconductor layers

Knoff W., Dziawa P., Osinniy V., Taliashvili B., Domuchowski V., Łusakowska E., Świątek K., Story T.

Materials Science Poland

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2007

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Vol. 25, No. 2

293--300

EN

Magnetic properties of thin layers of p-Ge1-xMnxTe (x < 0.2) semimagnetic (diluted magnetic) semiconductor exhibiting carrier induced ferromagnetism were experimentally studied. The layers were grown on BaF2 (111) substrates by molecular beam epitaxy technique. X-ray diffraction analysis performed at room temperature revealed monocrystalline (111)-oriented rhombohedral (exhibiting ferroelectric properties) crystal structure of Ge1-xMnxTe layers in the entire range of Mn content studied. The examination of the magnetic properties of the layers carried out by superconducting SQUID magnetometry and ferromagnetic resonance technique showed the ferromagnetic transition with the Curie temperature in the range 10-100 K depending on the Mn content and the hole concentration. Contrary to polycrystalline GeMnTe layers, it was experimentally found that in monocrystalline layers of GeMnTe an easy magnetization axis is directed along a normal to the layer plane. This effect is discussed in terms of strain present in these layers due to thermal expansion coefficients mismatch between the substrate and the GeMnTe layer.

4

Magnetic properties of (Eu,Gd)Te semiconductor layers

Dziawa P., Osinniy V., Dobrowolski W., Dybko K., Łusakowska E., Taliashvili B., Story T., Smits C.J.P., Swagten H.J.M.

Materials Science Poland

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2006

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Vol. 24, No. 3

777--781

EN

In (Eu,Gd)Te semiconductor alloys a well known antiferromagnetic semiconductor compound EuTe is transformed into n-type ferromagnetic alloy. This effect is driven by the RKKY interaction via conducting electrons created due to substitution of Gd3+ for Eu2+ ions. It is expected that due to the high degree of electron spin polarization (Eu,Gd)Te can be exploited in new semiconductor spintronic heterostructures as a model injector of spin-polarized carriers. The (Eu,Gd)Te monocrystalline layers with Gd content up to 5 at. % were grown by MBE on BaF2 (111) substrates with either PbTe or EuTe buffer layers. The measurements of magnetic susceptibility and magnetization revealed that the ferromagnetic transition with the Curie temperature TC=11- 15 K is observed in (Eu,Gd)Te layers with n-type metallic conductivity. An analysis of the magnetization of (Eu,Gd)Te was carried out in a broad range of magnetic fields applied along various crystal directions both in- and out-of layer plane. It revealed, in particular, that a rapid low field ferromagnetic response of (Eu,Gd)Te layer is followed by a paramagnetic-like further increase towards the full saturatio