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1
Content available Metal-Insulator Transition in Zinc-Doped LaSrCuO
100%
Malinowski A. , Cieplak M. , Berkowski M. , Plesiewicz W. , Skośkiewicz T.
Acta Physica Polonica A
|
2006
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tom 109
|
nr 4-5
617-621
EN
The magnetotransport in the vicinity of the metal-insulator transition in La_{1.85}Sr_{0.15}Cu_xZn_{1-x}O_4 is studied in the mK temperature range. Both longitudinal and transverse magnetoresistance are negative indicating the importance of spin effects. The magnitude of transverse magnetoresistance is larger than the magnitude of longitudinal magnetoresistance, indicating the absence of positive orbital magnetoresistance, in sharp contrast to strongly underdoped La_{2-x}Sr_xCuO_4. Both transverse and longitudinal magnetoresistance are proportional to the relative change of zero-field conductivity. This suggests that low-temperature localization of carriers may originate in the spin-disorder scattering on the spin droplets around Zn-impurities.
2
Content available remote Influence of Bound Magnetic Polarons on Magnetic and Electrical Properties in Metallic n-Cd_{0.95}Mn_{0.05}Se
86%
Głód P. , Sawicki M. , Dietl T. , Skośkiewicz T. , Lenard A. , Plesiewicz W.
Acta Physica Polonica A
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1995
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tom 87
|
nr 1
173-175
EN
Doping-induced contribution to the millikelvin magnetic susceptibility of Cd_{0.95}Mn_{0.05}Se:In has been found to undergo a maximum at n ≈ 2n_{c}, and to vanish for n ≥ 8n_{c}, where n_{c} is the electron concentration corre­sponding to the metal-insulator transition. This confirms the presence, also in the metallic phase, of bound magnetic polarons. Their slow dynamics may account for hysteresis visible in our magnetoresistance data.
3
Content available remote Search for Dimensional Effects in Spin-Glass Transition in Thin Cd_{1-x}Mn_{x}Te Multilayers
86%
Sawicki M. , Dietl T. , Skośkiewicz T. , Karczewski G. , Wojtowicz T. , Kossut J.
Acta Physica Polonica A
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1995
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tom 88
|
nr 5
1038-1042
EN
SQUID magnetic measurements of CdTe/Cd_{1-x}Mn_{x}Te, x ≃ 0.5, multi-layers with different CdMnTe layer thickness w reveal the persistence of the spin-glass irreversibilities down to ≃ 16 Å thin layers, i.e., well beyond the previously postulated 40 Å as a quasi-2D threshold. The freezing temperature T_{f} is found to be a monotonic function of w, and it obeys a scaling law T_{f} ∝ w^{a}, with a 0.8 similar to that for canonical spin-glasses. Magnetic properties of all studied structures are found to be independent of the orientation of the magnetic field.
4
Content available remote Search for Dimensionality Crossover of Spin-Glass Freezing in Superlattices of Cd_{0.50}Mn_{0.50}Te/CdTe
86%
Sawicki M. , Dietl T. , Karczewski G. , Wojtowicz T. , Kossut J. , Skośkiewicz T.
Acta Physica Polonica A
|
1996
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tom 90
|
nr 5
919-922
EN
SQUID measurements of the time decay of the thermoremanent magnetization (field-cooled in 1000 Oe) at long time scale, 10^{2} < t < 10^{5} s, are presented for MBE grown Cd_{0.50}Mn_{0.50}Te. We found that for both thin (32 Å) and thick (2500 Å) layers the spin-glass dynamics is characterized by a similar value of k = -(1/T_{f})(dT_{f}/dlogt) > 0.05, indicating the absence of the phase transition at nonzero temperature under the experimental conditions.
5
Content available remote Conductance Fluctuations in Microstructures of HgCdMnTe Bicrystals
72%
Grabecki G. , Lenard A. , Plesiewicz W. , Jaroszyński J. , Cieplak M. , Skośkiewicz T. , Dietl T. , Kamińska E. , Piotrowska A. , Bulka B.
Acta Physica Polonica A
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1991
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tom 80
|
nr 2
307-310
EN
Microscopic four-contact probes to semimagnetic HgCdMnTe grain-boundary inversion layers have been photolithographically patterned. Magnetoresistance measurements performed on these samples revealed aperiodic conductance fluctuations of the magnitude of the order of e^{2}/h. Quantitative analysis of both fluctuation amplitude and their mean period indicate that we have approached the mesoscopic regime in our system. This opens new possibilities in studies of spin-subsystem dynamics in semimagnetic semiconductors.
6
Content available remote Mesoscopic Phenomena in Microstructures of IV-VI Epilayers
72%
Grabecki G. , Dietl T. , Plesiewicz W. , Lenard A. , Skośkiewicz T. , Kamińska E. , Piotrowska A. , Papis E. , Frank N. , Bauer G.
Acta Physica Polonica A
|
1995
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tom 87
|
nr 2
551-554
EN
Magnetoresistance measurements of photolithographically patterned PbSe and Pb-{1-y}Mn_{x}Se microstructures were performed. Reproducible mag­netoconductance fluctuations with the amplitude increasing with decreasing temperature were observed. Unexpectedly, these fluctuations contain a com­ponent periodic in the magnetic field, and their magnitude is greater than that expected from the current theory of the universal conductance fluctua­tions. Possible explanations are discussed.
7
Content available remote Second Harmonic Generation in Spin-Glass Microstructures and Fabrication of Microstructures in IV-VI Epilayers
58%
Grabecki G. , Dietl T. , Cieplak M. , Plesiewicz W. , Lenard A. , Skośkiewicz T. , Kamińska E. , Piotrowska A. , Żarecka R. , Springholz G. , Bauer G.
Acta Physica Polonica A
|
1993
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tom 84
|
nr 4
781-784
EN
We studied magnetoconductance of two different mesoscopic systems: microregions containing two-dimensional electron gas adjacent to a grain-boundary plane in bicrystals of Hg_{0.79}Cd_{0.19}Mn_{0.02}Te and photolithographically patterned microstructures of Pb_{1-x}Mn_{x}Se. In both systems universal conductance fluctuations and generation of the second-harmonic voltage were observed at T ≤ 1 K. Moreover, in the former system the second harmonic signal exhibited distinct rise when the sample was cooled below the spin-glass freezing temperature (100 mK).
8
Content available remote Conductance Fluctuations in Quantum Wires of n-CdTe and n-Cd_{1-x}Mn_{x}Te
58%
Jaroszyński J. , Wróbel J. , Sawicki M. , Skośkiewicz T. , Karczewski G. , Wojtowicz T. , Kossut J. , Dietl T. , Kamińska E. , Papis E. , Barcz A. , Piotrowska A.
Acta Physica Polonica A
|
1995
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tom 88
|
nr 5
1000-1004
EN
We present millikelvin studies of magnetoconductance in submicron wires of In-doped n^{+}-CdTe and n^{+}-Cd_{0.99}Mn_{0.01}Te epilayers. Weak-field magnetoresistance which arises from quantum localization as well as universal conductance fluctuations have been observed. The exchange coupling to magnetic impurities is shown to decrease the correlation field of the fluctuations. This novel effect is interpreted by invoking a new driving mechanism of the magnetoconductance fluctuations - the redistribution of the electrons between energy levels of the system, induced by the giant s-d spin-splitting of the electronic states.
9
Content available remote Dimensional Crossovers in Magnetoresistance of Submicron Films and Wires of CdTe:In
58%
Jaroszyński J. , Wróbel J. , Sawicki M. , Skośkiewicz T. , Karczewski G. , Wojtowicz T. , Kossut J. , Dietl T. , Kamińska E. , Papis E. , Piotrowska A. , Duś R. , Nowakowski R.
Acta Physica Polonica A
|
1996
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tom 90
|
nr 5
1027-1031
EN
We present millikelvin studies of magnetoresistance for epitaxial films and wires of CdTe:In. In comparison to the data with theoretical predictions for the weakly localized regime we put into the evidence the presence of the temperature-induced dimensional crossovers in the studied systems. Our measurements probe the electron phase-breaking rate and indicate that the main dephasing mechanism arises from electron scattering from thermal fluctuations of three- or two-dimensional electron liquid.
10
Content available remote Conductance Anomalies in Strained Quantum Wires: the Case of PbSe and PbTe
58%
Grabecki G. , Wróbel J. , Dietl T. , Sawicki M. , Skośkiewicz T. , Papis E. , Kamińska E. , Piotrowska A. , Frank N. , Ueta Y. , Sprinholtz G. , Bauer G.
Acta Physica Polonica A
|
1996
|
tom 90
|
nr 4
797-800
EN
We show that conducting edge channels are formed in free standing wires of PbSe/BaF_{2} and PbTe/BaF_{2} as temperature is lowered. The effect results from spatially inhomogeneous strain caused by a difference between the thermal expansion coefficients of the epilayer and the substrate. The presence of the edge channels can explain anomalous mesoscopic effects observed previously in these wires.
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