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  1. 30 Sawicki M.

  2. 14 Dietl T.

  3. 6 Minikayev R.

  4. 6 Paszkowicz W.

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1
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Magnetic Properties of (Ga,Mn)As

100%
Sawicki M.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
119-130
EN
A review is given of experimental findings and theoretical understanding of micromagnetic properties of zinc-blende ferromagnetic semiconductors, with (Ga,Mn)As taken as a sole example. It is emphasised that the Zener p-d model explains quantitatively the effect of strain on the easy axis direction as well as it predicts correctly the presence of the reorientation transition, observed as a function of hole concentration and temperature. Possible suggestions put forward to explain the existence of in-plane uniaxial magnetocrystalline anisotropy are then quoted.
2
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Magnetism and Superconductivity in Nd_{0.81}Sr_{0.19}MnO_3/YBa_2Cu_3O_7 Superlattices

52%
Komissarov I., Przysłupski P., Dłużewski P., Sawicki M.
Acta Physica Polonica A
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2004
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vol. 105
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issue 1-2
127-132
EN
We report on the growth, structural and magnetic characterization of Nd_{0.81}Sr_{0.19}MnO_3/YBa_2Cu_3O_7 (NSMO/YBCO) superlattices. The NSMO system for the doping level of x=0.19 is a ferromagnetic insulator. Multilayers with a fixed NSMO thickness of 13 unit cells and a varying YBCO layer thickness from 2 unit cells to 6 unit cells were sputtered on LaAlO_3 substrates. An onset of superconducting transition is seen starting from the multilayer with 3 unit cells of YBCO layer thickness. Hysteresis loops recorded above and below the superconducting transition show a signature of interlayer exchange coupling.
3
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Magnetic Phase Diagram of Zinc-Blende Cd_{1-x}Mn_{x}Se

52%
Sawicki M., Furdyna J., Luo H.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
923-926
EN
The paper reports first magnetic measurements performed on MBE grown epilayers of zinc-blende Cd_{1-x}Mn_{x}Se. For all samples studied in the concentration range 0.24 < x < 0.63 we find at low temperatures a history-dependent magnetic response, suggesting a transition to a spin-glass-like state. The central result of the paper is the presentation of a new, complete magnetic phase diagram for this material.
4
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Conductivity Near the Metal-to-Insulator Transition in Cd_{1-x}Mn_{x}Se:Sc

46%
Głód P., Sawicki M., Lenard A., Dietl T., Plesiewicz W.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
389-392
EN
Earlier studies of transition metal impurities in II-VI compounds suggest that Sc acts as a resonant donor. We performed Hall effect and conductivity measurements of CdSe:Sc and Cd_{0.95}Mn_{0.05}Se:Sc. The results, particularly the critical concentration of the metal-to-insulator transition, turned out to be similar to those obtained previously for Cd_{1-x}Mn_{x}Se doped with hydrogenic-like impurities, such as In and Ga. Therefore, if the ground state of Sc impurity is indeed located above the bottom of the conduction band, our data demonstrate that the metal-to-insulator transition is primarily driven by the scattering, i.e. it corresponds to the Anderson localization.
5
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Light-Controlled Transport in Doped Diluted Magnetic Semiconductors near Localization Boundary

46%
Głód P., Dietl T., Wojtowicz T., Sawicki M., Miotkowski I.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
657-660
EN
We report milikelvin studies of light induced metastable changes of the conductivity of the In doped Cd_{0.95}Mn_{0.05}Te_{0.97}Se_{0.03} crystals in the vicinity of the metal-insulator transition.
6
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Magnetic Nature of a Ni Dopant in La_{1.85}Sr_{0.15}CuO_4: Spin-Glass Behavior

39%
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.
7
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Influence of Bound Magnetic Polarons on Magnetic and Electrical Properties in Metallic n-Cd_{0.95}Mn_{0.05}Se

39%
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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vol. 87
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issue 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.
8
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Interval Identification of FMR Parameters for Spin Reorientation Transition in (Ga,Mn)As

39%
Gutowski M., Stefanowicz W., Proselkov O., Sawicki M., Żuberek R., Sadowski J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1228-1230
EN
In this work we report results of ferromagnetic resonance studies of a 6% 15nm (Ga,Mn)As layer, deposited on (001)-oriented GaAs. The measurements were performed with in-plane oriented magnetic field, in the temperature range between 5 K and 120 K. We observe a temperature induced reorientation of the effective in-plane easy axis from [\overline{1}10] to [110] direction close to the Curie temperature. The behavior of magnetization is described by anisotropy fields, H_{eff} (=4π M-H_{2⊥}), H_{2∥}, and H_{4∥}. In order to precisely investigate this reorientation, numerical values of anisotropy fields have been determined using powerful - but still largely unknown - interval calculations. In simulation mode this approach makes possible to find all the resonance fields for arbitrarily oriented sample, which is generally intractable analytically. In "fitting" mode we effectively utilize full experimental information, not only those measurements performed in special, distinguished directions, to reliably estimate the values of important physical parameters as well as their uncertainties and correlations.
9
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Superconductivity and Magnetism in Nd_{0.5}Sr_{0.5}MnO_3/YBa_2Cu_3O_7 Superlattices

39%
Tsarou A., Paszkowicz W., Minikayev R., Dłużewski P., Sawicki M., Przysłupski P.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
179-183
EN
We report the synthesis and characterization of Nd_{0.5}Sr_{0.5}MnO_3/YBa_2Cu_3O_7 superlattices. X-ray diffraction studies show that the superlattices are [001] oriented. We observe that the magnetic ground state of Nd_{0.5}Sr_{0.5}MnO_3 system in a multilayered structure is strongly dependent on the substrate.
10
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Magnetic Properties of Molecular Beam Epitaxy Grown High x Cd_{1-x}Mn_{x}Te

39%
Sawicki M., De Groot P., Brummell M., Tomka G., Ashenford D., Lunn B.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
745-748
EN
Magnetization measurements performed on molecular beam epitaxy grown Cd_{1-x}Mn_{x}Te structures revealed basically similar magnetic properties of thick epilayers to their bulk counterparts. However, remarkably different properties were detected for a superlattice. These are attributed to a smearing out of the Mn profile in the superlattice.
11
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Search for Dimensionality Crossover of Spin-Glass Freezing in Superlattices of Cd_{0.50}Mn_{0.50}Te/CdTe

39%
Sawicki M., Dietl T., Karczewski G., Wojtowicz T., Kossut J., Skośkiewicz T.
Acta Physica Polonica A
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1996
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vol. 90
|
issue 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.
12
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Search for Dimensional Effects in Spin-Glass Transition in Thin Cd_{1-x}Mn_{x}Te Multilayers

39%
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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vol. 88
|
issue 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.
13
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Signature of the Spin Triplet Phase in La_{0.7}Sr_{0.3}MnO_3/Yba_2Cu_3O_7/La_{0.7}Sr_{0.3}MnO_3 Trilayers

39%
Przyslupski P., Dybko K., Werner-Malento K., Aleshkevych P., Wojcik M., Sawicki M.
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|
issue 2
313-315
EN
Differential dynamical subgap transport measurements were performed on LSMO/YBCO/LSMO trilayers to probe local evolution of the Andreev bound states which are manifested as the zero bias conductance peak. Dynamical conductivity dI/dV vs. magnetic field measured in current in plane and current perpendicular to plane geometries show nonmonotonic behavior with maximum at about 500 Oe. The shape of the zero bias conductance peak measured in current in plane geometry is sharp, whereas zero bias conductance peak measured in current perpendicular to plane geometry demonstrates V shape. These shapes of the zero bias conductance peak were predicted theoretically for unconventional p-wave spin triplet phase superconductor and superconductor with d-wave symmetry of the order parameter, respectively.
14
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Magnetic Characterization of Molecular Beam Epitaxy Grown Cd_{1_{x}}Mn_{x}Te Structures

33%
Sawicki M., Kolesnik S., Wojtowicz T., Karczewski G., Janik E., Kutrowski M., Żakrzewski A., Dynowska E., Dietl T., Kossut J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
169-172
EN
The paper reports on the application of SQUID magnetometry to probe magnetic ion distribution in epilayers and at interfaces of diluted magnetic semiconductors. We present also new results on the possible influence of the magnetic confinement on the formation of the spin-glass phase, and on antiferromagnetic phase transition in zinc-blende MnTe.
15
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Properties and Characterization of ALD Grown Dielectric Oxides for MIS Structures

33%
Gierałtowska S., Sztenkiel D., Guziewicz E., Godlewski M., Łuka G., Witkowski B., Wachnicki Ł., Łusakowska E., Dietl T., Sawicki M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
692-695
EN
We report on an extensive structural and electrical characterization of undergate dielectric oxide insulators Al_2O_3 and HfO_2 grown by atomic layer deposition. We elaborate the atomic layer deposition growth window for these oxides, finding that the 40-100 nm thick layers of both oxides exhibit fine surface flatness and required amorphous structure. These layers constitute a base for further metallic gate evaporation to complete the metal-insulator-semiconductor structure. Our best devices survive energizing up to ≈ 3 MV/cm at 77 K with the leakage current staying below the state-of-the-art level of 1 nA. At these conditions the displaced charge corresponds to a change of the sheet carrier density of 3 × 10^{13} cm^{-2}, which promises an effective modulation of the micromagnetic properties in diluted ferromagnetic semiconductors.
16
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Electronic Properties of Thin HfO_2 Films Fabricated by Atomic Layer Deposition on 4H-SiC

33%
Taube A., Gierałtowska S., Gutt T., Małachowski T., Pasternak I., Wojciechowski T., Rzodkiewicz W., Sawicki M., Piotrowska A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
696-698
EN
Applicability of thin HfO_2 films as gate dielectric for SiC MOSFET transistor is reported. Layers characterisation was done by means of atomic force microscopy and scanning electron microscopy, spectroscopic ellipsometry and C-V and I-V measurements of MIS structures. High permittivity dielectric layers were deposited using atomic layer deposition. Investigation showed high value of κ = 15 and existence of high density surface states (5 × 10^{12} eV^{-1} cm^{-2}) on HfO_2/SiC interface. High leakage current is caused probably due to low conduction band offset between hafnium oxide and silicon carbide.
17
Publication available in full text mode
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MnAs Overlayer on GaN(000_1)-(1 x 1) - Its Growth, Morphology and Electronic Structure

33%
Kowalski B., Kowalik I., Iwanowski R., Łusakowska E., Sawicki M., Sadowski J., Grzegory I., Porowski S.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
645-650
EN
MnAs layer has been grown by means of MBE on the GaN(000_1)-(1 x 1) surface. Spontaneous formation of MnAs grains with a diameter of 30-60 nm (as observed by atomic force microscopy) occurred for the layer thickness bigger than 7 ML. Ferromagnetic properties of the layer with Curie temperature higher than 330 K were detected by SQUID measurements. Electronic structure of the system was investigated in situ by resonant photoemission spectroscopy for MnAs layer thickness of 1, 2, and 8 ML. Density of the valence band states of MnAs and its changes due to the increase in the layer thickness were revealed.
18
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Growth of GaN Metalorganic Chemical Vapour Deposition Layers on GaN Single Crystals

33%
Pakula K., Baranowski J. M., Stępniewski R., Wysmołek A., Grzegory I., Jun J., Porowski S., Sawicki M., Starowieyski K.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
861-864
EN
The homoepitaxial growth of GaN layers has been achieved for the first time. Bulk GaN single crystals which have been used as a substrate have been grown from diluted solution of atomic nitrogen in the liquid gallium at 1600°C and at nitrogen pressure of about 15-20 kbar. It is shown that a terrace growth of GaN epitaxial layer has been realized. The high quality of the GaN film has been confirmed by luminescence measurements. The analysis of donor-acceptor and exciton luminescence is presented.
19
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Electron Localization in Sb-Doped Si/SiGe Superlattices

33%
Dietl T., Jaroszyński J., Sawicki M., Głód P., Wróbel J., Stöger G., Brunthaler G., Bauer G., Schäffler F.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
699-702
EN
Millikelvin studies of in-plane magnetoconductance in short period Si/Ge:Sb superlattices have been carried out in order to examine the effect of anisotropy on quantum localization. The field-induced metal-to-insulator transition has been observed, indicating the existence of extended states. This suggests that despite anisotropy as large as D_{∥}/D_{⊥} ≈ 10^{3} the system behaves as 3D in respect of localization by disorder.
20
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Structure and Magnetic Characterization οf BiFeO_3/YBa_2Cu_3O_7 Bilayers

33%
Werner-Malento K., Tsarou A., Dluzewski P., Paszkowicz W., Minikayev R., Sawicki M., van der Beek K., Konczykowski M., Przyslupski P.
Acta Physica Polonica A
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2009
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vol. 115
|
issue 1
95-97
EN
Bilayered epitaxial BiFeO_3/YBa_2Cu_3O_7 films were fabricated on (100) [(LaAlO_3)_{0.3}(Sr_2TaAlO_6)_{0.7}] substrates by sputtering method. For structural comparison the bilayered BiFeO_3/La_{0.67}Sr_{0.33}MnO_3 films were also deposited on (100) SrTiO_3 substrates. A weak ferromagnetic moment is observed in BiFeO_3/YBa_2Cu_3O_7 films. The mechanism responsible for weak ferromagnetic moment arises presumably from the epitaxy strain induced canted antiferromagnetic structure.
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