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1
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Magnetic Nature of a Ni Dopant in La_{1.85}Sr_{0.15}CuO_4: Spin-Glass Behavior

100%
Malinowski A., Bezusyy V., Minikayev R., Paszkowicz W., Dziawa P., Syryanyy Y., Sawicki M.
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issue 2
244-248
EN
The magnetic properties of La_{1.85}Sr_{0.15}CuO_4 doped with Ni was investigated in the field up to 5 T and in the temperature range from 2 K to 400 K using both dc and ac techniques. For Ni content larger than 0.05 the system exhibits irreversibility of low-field susceptibility χ(T) below a certain temperature depending on y and a cusp at T_{g} in χ(T) measured after zero-field cooling. The decay of remnant magnetization below T_{g} with time is described by a stretched-exponential function. In accordance with scaling theory, all the χ(T) data for y = 0.50 sample taken in the vicinity of T_{g} at different fields collapse onto two separate curves when plotted as q|t|^{-β} vs. B^2 |t|^{-β - γ}, where q is the spin-glass order parameter, t = (T - T_{g})/T_{g}, and β and γ are the critical exponents. All these features taken together reveal existence of spin-glass phase below T_{g}. Variation of T_{g} with y is linear below y = 0.25 and T_{g} extrapolates to 0 K for y → 0 what strongly suggests that spin-glass phase extends into superconducting region of the phase diagram.
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New materials for thermoelectric generators based on PbTe-MnTe and PbTe-CdTe semiconductor alloys and nanocomposites

100%
Story T., Dybko K., Dziawa P., Mycielski A., Szczerbakow A., Szot M.
Biuletyn Polskiego Stowarzyszenia Wodoru i Ogniw Paliwowych
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2011
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issue 6
64-69
EN
New trends in the field of thermoelectrics are discussed for PbTe-based semiconductor thermoelectric materials exhibiting density of states engineering effects strongly enhancing thermoelectric power (PbMnTe) and spontaneous formation of nano-scale two-phase crystal structures (PbTeCdTe) – technologically scalable realization of electron crystal - phonon glass concept of new thermoelectric materials.
3
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From Cuprate to Nickelate: Evolution of the Normal State Properties with Ni from La_{1.85}Sr_{0.15}CuO_4 to La_{1.85}Sr_{0.15}NiO_4

100%
Bezusyy V., Malinowski A., Minikayev R., Paszkowicz W., Dziawa P., Gorzelniak R.
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issue 2
402-405
EN
The influence of Ni doping on the normal-state pseudogap in La_{1.85}Sr_{0.15}CuO_4 is studied by dc magnetic susceptibility measurements, accompanied by X-ray powder diffraction analysis and resistivity measurements. The measurements are carried out on the polycrystalline La_{1.85}Sr_{0.15}Cu_{1-y}Ni_yO_4 samples in the whole doping range from y=0.01 up to y=1. The temperature of pseudogap opening is found to decrease above y=0.05 and to vanish when y exceeds 0.07. At small Ni content, up to y=0.07, the magnetic moment induced by Ni is constant and equal to 0.7 μ_{B} per Ni, while for larger y it increases abruptly and reaches about 1.6 μ_{B} per Ni ion for y = 0.5. The dependence of the normal-state resistivity on temperature evolves smoothly from the metallic-like for small y, to the variable range hopping, described by the Mott law with the exponent 1/4, for samples with y>0.15.
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Photoemission Electronic Spectra οf CdTe/Pb_{0.95}Eu_{0.05}Te/CdTe

100%
Orlowski B., Dziawa P., Gas K., Reszka A., Mickievicius S., Thiess S., Drube W.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
960-963
EN
The synchrotron radiation was used to apply tunable high energy X-ray photoemission spectroscopy for investigation of electronic structure of semiconductor nanostructure CdTe/Pb_{0.95}Eu_{0.05}Te/CdTe/GaAs(001) top part. The Pb_{0.95}Eu_{0.05}Te (6 nm thick) was buried under thin (22 nm) top layer of CdTe transparent for part of electrons photoemitted from Pb_{0.95}Eu_{0.05}Te buried layer. The top layer of CdTe was sputtered by Ar ion bombardment for surface cleaning and for leaving the thickness of CdTe more transparent for photoelectrons emitted from buried layer. For these thickness of the top layer the photoemission energy distribution curves corresponding to the valence band and core levels electrons of the buried layer atoms were measured with application of synchrotron radiation of energy hν = 3510 eV. The measured spectra corresponding to the buried layer atoms were observed in the valence band region and in the high binding energy region for core levels of Pb 4f, Pb 3d. The valence band contribution and core levels Cd 4d and Cd 3d were obtained mainly from top cover layer. Measured Te 4d, Te 3d and Te 4d spectra possess contribution as well from top cover layer as from the buried layer. The amount of Eu atoms was to small to be reasonable detected and presented in the paper.
5
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Magnetic Force Microscopy Study of Zn_{1-x}Co_{x}O Nanowires Grown by Rapid Thermal Evaporation

84%
Aleszkiewicz M., Fronc K., Aleszkiewicz P., Zaleszczyk W., Dziawa P., Wojciechowski T., Wojtowicz T., Karczewski G.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
865-867
EN
In this work we studied domain structure of Zn_{1-x}Co_{x}O nanowires which are single arms of tetrapode crystals. The as-grown material exhibits hysteretic behavior even at room temperature as revealed by SQUID mesurements. In order to get insight into the magnetic properties of individual tetrapodes they were dismembered into nanowires of nanometric diameters, deposited on a flat substrate and imaged by magnetic force microscopy. A magnetic interaction between the magnetic force microscopy probe and single nanowires has been detected which confirms that nanometric volume of the material possesses a magnetic moment. The magnetic force microscopy contrast is attractively independent of the tip magnetization direction which indicates that shape anisotropy of nanowires is not strong enough to prevent occurrence of tip-induced magnetic field disturbance.
6
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Fano Resonance of Eu^{2+} and Eu^{3+} in (Eu,Gd)Te MBE Layers

84%
Orlowski B., Kowalski B., Dziawa P., Pietrzyk M., Mickievicius S., Osinniy V., Taliashvili B., Kowalik I., Story T., Johnson R.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
803-807
EN
Resonant photoemission spectroscopy, with application of synchrotron radiation, was used to study the valence band electronic structure of clean surface of (EuGd)Te layers. Fano-type resonant photoemission spectra corresponding to the Eu 4d-4f transition were measured to determine the contribution of 4f electrons of Eu^{2+} and Eu^{3+} ions to the valence band. The resonant and antiresonant photon energies of Eu^{2+} ions were found as equal to 141 V and 132 eV, respectively and for Eu^{3+} ions were found as equal to 146 eV and 132 eV, respectively. Contribution of Eu^{2+}4f electrons was found at the valence band edge while for Eu^{3+} it was located in the region between 3.5 eV and 8.5 eV below the valence band edge.
7
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Features of Energy Spectrum of Pb_{1-x}Mn_xTe Doped with V

84%
Artamkin A., Dobrovolsky A., Dziawa P., Story T., Slynko E., Slynko V., Ryabova L., Khokhlov D.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
151-156
EN
Recently new effects that are not characteristic of undoped lead telluride, such as the Fermi level pinning, giant negative magnetoresistance, were observed in Pb_{1-x}Mn_xTe alloys doped with transition and rare earth elements - Cr, Mo, Yb. We have studied transport and magnetic properties of Pb_{1-x}Mn_xTe doped with another transition element - vanadium. A series of Pb_{1-x}Mn_xTe(V) samples of different composition and degree of doping was investigated. It was observed that the resistivity demonstrates activation behavior at low temperatures for the samples with considerable amount of vanadium as well as for the samples without vanadium. The activation energy is proportional to the Mn content. In some of the samples, photoconductivity was observed at low temperatures. The results are discussed in terms of a model assuming formation of the impurity level by the vanadium impurity and the effect of the Fermi level pinning by this level.
8
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Fano Resonance Investigation of PbTe Layers Containing Eu and Gd Ions

84%
Orlowski B., Osinniy V., Dziawa P., Pietrzyk M., Kowalski B., Taliashvili B., Story T., Johnson R.
Acta Physica Polonica A
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2008
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vol. 114
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issue 2
351-356
EN
The Fano resonance photoemission studies of Gd/(Pb, Gd)Te layers using synchrotron radiation were carried out and the electronic structure parameters like binding energies of Gd^{3+} 4f and 5p shells, resonance and antiresonance energies for Gd^{3+} were determined. The presence of Eu^{3+} ions was observed in the (Pb, Eu)Te and (Eu, Gd)Te layers grown by MBE technique. The comparison of data for (Pb, Gd)Te compound with corresponding data for (Eu, Gd)Te and (Pb, Eu)Te layers indicates that we are not able to distinct the Eu^{3+}4f and Gd^{3+}4f electrons contribution to the valence band photoemission spectra because of small content od Gd and similar binding energy values. The key parameters allowing to prove exactly the presence of either Eu^{3+} or Gd^{3+} are the resonance and antiresonance energies which are significantly different for these ions and equal to 143 eV/137 eV and 150 eV/142 eV, respectively.
9
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Interlayer Exchange Coupling in Semiconductor EuS-PbS Ferromagnetic Wedge Multilayers

84%
Kowalczyk L., Wrotek S., Dziawa P., Osinniy V., Szot M., Story T., Sipatov A., Volobuev V., Fedorov A.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
225-231
EN
Antiferromagnetic interlayer coupling between ferromagnetic layers of EuS via nonmagnetic PbS spacer layer was experimentally studied in EuS-PbS wedge multilayers grown on KCl (001) substrates with EuS thickness of 6 nm and PbS thickness varying in the wedges in the range 0.3-6 nm (i.e. n=1-20 monolayers). Measurements of magnetic hysteresis loops of EuS-PbS multilayers performed in the temperature range 5-30 K by superconducting (SQUID) and magneto-optical magnetometers revealed a rapid increase in saturation magnetic field in multilayers with PbS spacer thinner than about 1.5 nm. It shows a monotonic increase in interlayer coupling strength with a decreasing PbS spacer thickness, in qualitative agreement with 1/2^n dependence predicted theoretically for semiconductor magnetic superlattices.
10
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Studies of Diluted Magnetic Semiconductor Sn_{1-x-y-z}Ge_{x}Mn_{y}Gd_{z}Te

84%
Sichkovskyi V., Radchenko M., Lashkarev G., Slyn'ko V., Slyn'ko E., Knoff W., Domukhovski V., Dziawa P., Story T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
911-912
EN
Magnetization, anomalous Hall effect, thermoelectric power, magnetoresistance, and resistivity of Sn_{1-x-y-z}Ge_{x}Mn_{y}Gd_{z}Te (x = 0.039÷0.597, y = 0.077÷0.125, z = 0.0014÷0.028) mixed crystals were studied over the temperature range 4.2-300 K. The ferromagnetic order with Curie temperature 18-24 K was revealed.
11
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Magnetization Studies of Antiferromagnetic Interlayer Coupling in EuS-SrS Semiconductor Multilayers

84%
Samburskaya T., Sipatov A., Volobuev V., Dziawa P., Knoff W., Kowalczyk L., Szot M., Story T.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
133-136
EN
Temperature and magnetic field dependence of magnetization of EuS-SrS multilayers grown epitaxially on KCl (001) substrate is experimentally studied by superconducting magnetometry technique. In these lattice-matched semiconductor heterostructures EuS layers are ferromagnetic quantum wells whereas SrS layers are nonmagnetic spacer barriers. The multilayers composed of EuS layers with thickness 3.5-5 nm and SrS layers (thickness 0.5-10 nm) exhibit ferromagnetic transition at 17 K. In the multilayers with ultrathin SrS spacers (0.5-1 nm) a nonmonotonic temperature dependence of magnetization as well as a characteristic switching in magnetic hysteresis loops is observed. These experimental findings are explained considering antiferromagnetic interlayer coupling between ferromagnetic EuS layers via nonmagnetic SrS spacers. The strength of this coupling is determined based on model magnetization calculations.
12
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(Eu,Gd)Te - MBE Growth and Characterization

69%
Dziawa P., Taliashvili B., Domuchowski W., Łusakowska E., Arciszewska M., Demchenko I., Dobrowolski W., Dybko K., Fedorych O., Nadolny A., Osinniy V., Petrouchyk A., Story T.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
215-221
EN
Monocrystalline thin layers of (Eu,Gd)Te, n-type ferromagnetic semiconductor, were grown by molecular beam epitaxy technique on BaF_2 (111) substrates. Reflection high-energy electron diffraction, X-ray diffraction, and atomic force microscopy characterization proved epitaxial mode of growth and high crystal quality of the layers. Magnetic susceptibility and magnetic resonance measurements showed that in (Eu,Gd)Te layers ferromagnetic transition takes place at about 13 K. Electrical characterization carried out by the Hall effect and resistivity measurements revealed very high electron concentration of 10^{20}~cm^{-3} and sharp maximum of resistivity at transition temperature.
13
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Experimental and Theoretical Analysis οf PbTe-CdTe Solid Solution Grown by Physical Vapour Transport Method

69%
Szot M., Szczerbakow A., Dybko K., Kowalczyk L., Smajek E., Domukhovski V., Łusakowska E., Dziawa P., Mycielski A., Story T., Bukała M., Galicka M., Sankowski P., Buczko R., Kacman P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
959-961
EN
Bulk monocrystals of Pb_{1-x}Cd_{x}Te, with the Cd content x up to 0.11, were grown by physical vapour transport method. The structural, electrical and optical properties of these ternary crystals were studied experimentally and theoretically. All investigated samples exhibit rock-salt structure and high crystal quality, which was confirmed by X-ray rocking curve width parameter of about 100 arcsec. The decrease of the lattice parameter with increasing Cd content x was found experimentally, in agreement with ab initio calculations. The band structures of Pb_{1-x}Cd_{x}Te mixed crystals for x values up to 0.2 were calculated using tight binding approach. The calculated band gap in the L-point increases with the Cd content in qualitative agreement with photoluminescence measurements in the infrared. For all studied Pb_{1-x}Cd_{x}Te samples, the Hall effect and electrical conductivity measurements, performed in the temperature range from 4 to 300 K, revealed p-type conductivity.
14
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Physical Properties of ZnCoO Tetrapods and Nanofibers

69%
Gas K., Fronc K., Dziawa P., Knoff W., Wojciechowski T., Zaleszczyk W., Baranowska-Korczyc A., Morhange J., Paszkowicz W., Elbaum D., Karczewski G., Wojtowicz T., Szuszkiewicz W.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
868-870
EN
In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and nanofibers grown by a rapid thermal evaporation process and prepared by the electrospinning technique, respectively, were investigated and analyzed. Surface morphology of the samples was examined using scanning electron microscopy. X-ray diffraction measurements showed hexagonal wurtzite crystal structure of both types of investigated nanostructures. Both X-ray diffraction and Raman scattering data confirmed high phase purity of the samples. The magnetic properties studied with the use of the SQUID magnetometer confirmed a presence of ferromagnetic order in analyzed nanostructures. The observed photoluminescence spectra exhibited two groups of lines. The first one, in the ultraviolet spectral range, is due to the optical transitions close to ZnO band gap, the second one in the red region is most probably related to the Co^{2+} d-d internal transitions. The influence of native defects on the optical properties is also shown and discussed. All results reported here lead us to the conclusion that in the mixed crystal nanostructures obtained, a fraction of the Zn^{2+} ions is substituted by Co^{2+} ions.
15
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Ferromagnetic Transition in Ge_{1-x}Mn_{x}Te Layers

69%
Knoff W., Domukhovski V., Dybko K., Dziawa P., Jakieła R., Łusakowska E., Reszka A., Świątek K., Taliashvili B., Story T., Szałowski K., Balcerzak T.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
904-906
EN
Ferromagnetic transition temperature in thin layers of diluted magnetic (semimagnetic) semiconductor Ge_{1-x}Mn_{x}Te was studied experimentally by SQUID magnetometry method and analyzed theoretically for a model Ising-type diluted magnetic system with Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction. The key features of the experimentally observed dependence of the Curie temperature on Mn content (x ≤ 0.12) and conducting hole concentration p = (1-10) × 10^{21} cm^{-3} were reproduced theoretically for realistic valence band and crystal lattice parameters of p-Ge_{1-x}Mn_{x}Te taking into account short carrier mean free path encountered in this material and Ruderman-Kittel-Kasuya-Yosida mechanism with both delta-like and diffused character of spatial dependence of the exchange coupling between magnetic ions and free carriers.
16
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Epitaxial Growth and Optical Properties of PbTe/CdTe Semiconductor Heterostructures

69%
Szot M., Kowalczyk L., Smajek E., Domukhovski V., Domagała J., Łusakowska E., Taliashvili B., Dziawa P., Knoff W., Wiater M., Wojtowicz T., Story T.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1391-1396
EN
Growth optimization, optical and structural properties of PbTe/CdTe multilayers grown by molecular beam epitaxy on GaAs (001) as well as on BaF_2 (111) substrates is reported. An intense photoluminescence in the mid-infrared region is observed from PbTe quantum wells excited with 1.17 eV pulsed YAG:Nd laser. The energy of the emission peak shows blue shift with decreasing PbTe well width and has a positive temperature coefficient. The influence of thermal annealing on photoluminescence spectra of PbTe/CdTe multilayers grown on BaF_2 substrate is discussed.
17
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Magnetic Properties of Epitaxial (Ge,Mn)Te Thin Films with Varying Crystal Stoichiometry

69%
Knoff W., Domukhovski V., Dybko K., Dziawa P., Górska M., Jakieła R., Łusakowska E., Taliashvili B., Story T., Reszka A., Anderson J., Rotundu C.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1159-1165
EN
Magnetization of 1 μm thick ferromagnetic IV-VI (Ge, Mn)Te semiconductor layers with 10 at.% of Mn was studied by SQUID magnetometry method up to the magnetic fields of 70 kOe. The layers were grown on BaF₂ (111) substrates by molecular beam epitaxy with varying Te molecular flux, which permitted the control of layer stoichiometry and conducting hole concentration. X-ray diffraction and in situ electron diffraction characterization of layer growth and crystal structure revealed two-dimensional mode of growth and monocrystalline rhombohedral crystal structure of (Ge, Mn)Te layers. Controlling the layer stoichiometry influences the temperature dependence of magnetization with the ferromagnetic Curie temperature varying in Ge_{0.9}Mn_{0.1}Te layers from T_c=30 K (low Te flux) to T_c=42 K (high Te flux).
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