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1
Content available remote Magnetoresistive memory in ferromagnetic (Ga,Mn)As nanostructures
Wosiński T., Figielski T., Morawski A., Mąkosa A., Szymczak R., Wróbel J., Sadowski J.
Materials Science Poland
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2008
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Vol. 26, No. 4
1097--1104
EN
Magneto-resistive nanostructures have been investigated. The structures were fabricated by electron beam lithography patterning and chemical etching from thin epitaxial layers of the ferromagnetic semiconductor (Ga,Mn)As, in shape of three nanowires joined in one point and forming three-terminal devices, in which an electric current can be driven through any of the three pairs of nanowires. In these devices, a novel magneto-resistive memory effect has been demonstrated, related to a rearrangement of magnetic domain walls between different pairs of nanowires in the device consisting in that its zero-field resistance depends on the direction of previously applied magnetic field. The nanostructures can thus work as twostate devices providing basic elements of nonvolatile memory cells.
2
Content available remote Magnetic properties of silicon crystals implanted with manganese
Osinniy V., Misiuk A., Szot M., Świątek K., Bąk-Misiuk J., Barcz A., Jung W., Prujszczyk M., Story T.
Materials Science Poland
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2008
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Vol. 26, No. 3
751--757
EN
The influence of thermal treatment on magnetic properties of Si/Mn crystals grown by the Czochralski and by floating zone methods and implanted with Mn+ ions was studied by the SQUID magnetometry and electron spin resonance. Depending on thermal and hydrostatic pressure annealing conditions, three groups of Si/Mn samples were found: samples with only ferromagnetic phase, samples with ferromagnetic and paramagnetic contributions, and diamagnetic samples. The Curie temperature of ferromagnetic phase exceeds room temperature. The ESR and SQUID measurements suggest that Si/Mn implanted layer is magnetically inhomogeneous.
3
Content available remote Crystallization of (Th1-xUx)3As4 ferromagnetic semiconductor from the Ga flux
Wiśniewski P., Henkie Z., Pietraszko A.
Materials Science Poland
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2008
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Vol. 26, No. 4
933--938
EN
Crystals of n- or p-type heavily doped ferromagnetic semiconductor (Th1–xUx)3As4 (x = 0.67 and 0.80) were grown using a mineralization process in the Ga flux. An excess of As corresponding to MeAs2composition was necessary to grow the Me3As4 phase at temperature cycled between 1000 ºC and 1060 ºC. Dilution of U3As4 ferromagnet (Curie temperature TC = 198 K) with 20% of Th3As4 semiconductor (energy gap of 0.39 eV) reduced TC by 19%.
4
Content available remote 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.
5
Content available remote Domain-wall contribution to magnetoresistance in ferromagnetic (Ga,Mn)As film
Wosiński T., Pelya O., Figielski T., Mąkosa A., Morawski A., Sadowski J., Dobrowolski W., Szymczak R., Wróbel J.
Materials Science Poland
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2007
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Vol. 25, No. 2
351--358
EN
Simple magnetoresistive nanodevices formed by narrow constrictions of submicron width in the epitaxial film of a ferromagnetic (Ga,Mn)As semiconductor have been fabricated employing the electronbeam- lithography patterning and low-energy low-dose oxygen ion implantation. Low-temperature chargecarrier transport through the constrictions has been investigated and correlated with magnetic properties of the film. The constricted devices revealed abrupt jumps of a reduced resistance that appeared when the sweeping magnetic field crossed the regions of the coercive field of the film magnetization. In contrast, the non-constricted reference device displayed abrupt jumps of an enhanced resistance at the same values of magnetic field. We interpret the both features, whose positions on the magnetic-field scale reflect the hysteresis loop of magnetization, as manifestation of domain wall contribution to the (Ga,Mn)As film resistance. Presumably, the suppression of the weak localization effects by a domain wall located at the constriction results in a negative contribution of a domain wall to the resistance, while the spin-orbit interaction can be responsible for its positive contribution to the resistance.
6
Content available remote The RKKY coupling in diluted magnetic semiconductors
Werpachowska A.M., Wilamowski Z.
Materials Science Poland
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2006
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Vol. 24, No. 3
675--681
EN
This paper is an attempt to modify the classic Ruderman-Kittel-Kasuya-Yosida (RKKY) model to allow an analysis of the experimental data of the magnetic resonance measurements. In our calculations, we follow the treatment of the original authors of the RKKY model but include the finite band splitting, ?, as a phenomenological parameter. The RKKY exchange is not anymore of Heisenberg type and an anisotropy induced by the direction of carrier magnetization occurs.
7
Content available remote 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
8
Content available remote In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films
Sawicki M., Wang K.-Y., Edmonds K.W., Campion R.P., Staddon C.R., Farley N.R.S., Foxon C.T., Dietl T., Gallagher B.L.
Materials Science Poland
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2006
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Vol. 24, No. 3
627--631
EN
Using SQUID magnetometry we find that in (Ga,Mn)As films the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions. It can be rotated from the [-110] direction to the [110] direction by low temperature annealing and we show that this change is hole density related. We demonstrate that the magnitude of uniaxial anisotropy as well its dependence on the hole-concentration and temperature can be explained in terms of the p-d Zener model of the ferromagnetism assuming a small trigonal-like distortion.
9
Content available remote How to make GaMnAs with high ferromagnetic phase transition temperature?
Sadowski J., Domagała J. Z., Kanski J., Rodriguez C. H., Terki F., Charar S., Maude D.
Materials Science Poland
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2006
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Vol. 24, No. 3
617--625
EN
We analyze the role of structural defects in GaMnAs and demonstrate how their density can be drastically reduced by in situ post-growth annealing under As capping. Modifications of the magnetic, transport and structural properties of the annealed GaMnAs layers are presented. The main result is that the Curie temperatures are strongly increased relative those of the as-grown layers, from typically 70 - 80 K to 150 - 160 K. The annealed layers exhibit well-ordered smooth surfaces, suitable for further epitaxial overgrowth.
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