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1
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Numerical Studies of Magnetization Relaxation of Mn^{2+} in Zinc Blende Crystals

100%
Witowski A.
Acta Physica Polonica A
|
1992
|
vol. 82
|
issue 5
876-878
EN
The results of numerical simulation of magnetization relaxation of Mn^{2+} centers are presented. They show that the relaxation can be exponential in certain time intervals, with the relaxation rate related by a simple formula to the transition probabilities.
2
Content available remote

Magnetization Relaxation in a Four-Level System

100%
Witowski A.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 4
795-797
EN
The relaxation of magnetization in a four-level system (e.g. Co^{2+} in II-VI compounds) is discussed. It is shown that in the heat pulse experiment the slowest relaxation time is basically observed.
3
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Magnetization Relaxation in CdMnS

51%
Witowski A., Kutter C., Mac W., Wyder P.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 4
798-800
EN
The static magnetization measurements and relaxation of magnetization data for two Cd_{1-x}Mn_{x}S samples with different composition are presented. The magnetization is described by the modified Brillouin function. The magnetization relaxation shows unusual composition dependence. This behavior is explained by cross-relaxation to the unknown fast relaxing centers introduced during growth.
4
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Content available

An Estimate of the Energy Gap of InN from Measurements of the Fundamental Absorption Edge

51%
Trautman P., Pakuła K., Witowski A., Baranowski J.
Acta Physica Polonica A
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2005
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vol. 108
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issue 5
903-908
EN
Optical absorption between 0.4 and 4.5 eV of an InN layer grown by metalorganic vapour phase epitaxy on sapphire was measured at 296 and 12 K. The layer was also characterized by measurements of the Hall effect and of infrared reflectivity in the region of the plasma edge, which determined the concentration, mobility, and effective mass of electrons in the conduction band. The energy gap of InN was estimated to be equal to 0.9±0.2 eV. It was obtained from the spectral position of the fundamental absorption edge. Corrections to the energy gap resulting from the broadening of the fundamental absorption edge, from the Burstein-Moss shift, and from a band-gap shrinkage due to the impurity potential were included.
5
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The Relaxation of Mn Pairs in CdMnTe at High Magnetic Fields

51%
Strutz T., Witowski A., Wyder P.
Acta Physica Polonica A
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1991
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vol. 80
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issue 3
313-316
EN
The spin-lattice relaxation in CdMnTe at 4.7 K has been measured at high magnetic fields up to 24.5 T. At fields, where the ground state of nearest-neighbor exchange coupled Mn pairs changes due to energy level crossing, an increase in the relaxation rate is observed. This is attributed to the change of relaxation of nearest-neighbor Mn pairs. It proves that not only large size Mn clusters are involved in the relaxation as it has been shown previously, but also Mn pairs. It shows as well that the mixing of pair states is quite effective.
6
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Orientation Dependent Spin-Lattice Relaxation in CdMnSe

51%
Witowski A., Strutz T., Wyder P.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
536-538
EN
The magnetization dynamics of Cd_{1-x}Mn_{x}Se at 4.5 K as a function of magnetic field up to 22 T was measured using a nonresonant technique. For x = 0.01 the relaxation does not depend on orientation and in higher fields the relaxation rates are proportional to B^{3}. For x = 0.02 a dependence on orientation is observed. The difference does not depend on magnetic field. This suggests that either the interaction between Mn ions responsible for spin-lattice relaxation in Mn clusters is anisotropic, or the relaxing clusters are oriented in a given manner with respect to the c axis.
7
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Long-wavelength Optical Phonons in Cd_{1-x}Mn_{x}Se and Cd_{1-x}Fe_{x}Se Mixed Crystals

51%
Witowski A., Hausenblas M., Wyder P.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 2-3
311-314
EN
The results of FIR reflectivity measurements for CdMnSe and CdFeSe are presented. These results are described theoretically using Dynamic Dielectric Function in which two phonon modes are included. The composition dependencies of mode parameters and dielectric constant are discussed.
8
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Spin-Lattice Relaxation of CdMnTe, Measured with a Pick-up Coil in a High Magnetic Field

51%
Strutz T., Witowski A., Wyder P.
Acta Physica Polonica A
|
1991
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vol. 79
|
issue 1
149-153
EN
The spin-lattice relaxation (SLR) time of Cd_{1-x}Mn_{x}Te with x=0.008 is measured directly under electron spin resonance condition in a magnetic field of 8.9 T, using a pick-up coil. The SLR times are measured for different sample temperatures between 3.0K and 35K and compared with data of a more diluted sample with x=0.002. The SLR times are shorter than expected for single spin SLR. Moreover, the temperature dependence of the SLR time does not show any of the characteristic behaviours for single spin SLR. Thus, the observed SLR times are explained by cross relaxation of single spins with spin clusters.
9
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Infrared Optical and X-Ray Determination of Parameters for MOVPE Grown InAs_{1-x}Sb_{x} Epilayers

45%
Marszałek B., Zielińska-Rohozińska E., Bożek R., Stępniewski R., Witowski A.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
919-922
EN
The experimental room-temperature transmission of metalorganic vapour phase epitaxy grown InAsSb epilayers is compared with calculations based on a Kane model of the band structure. The band structure parameters are found. The composition of the samples was determined by X-ray diffraction.
10
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Changes of FIR Reflectivity of HgSe:Cr in a Magnetic Field

45%
Hausenblas M., Wyder P., Witowski A., Wittlin A., Mycielski A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
741-744
EN
The results of FIR magnetoreflectivity of HgSe:Cr are presented. They are interpreted using a classical dynamic dielectric function.
11
Content available remote

Do the Mixed Crystals HgSeS Exhibit the One-Mode Behavior?

39%
Szuszkiewicz W., Witowski A., Julien C., Balkanski M., Dybko K., Witkowska B., Mycielski A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
887-889
EN
The low-temperature far-infrared reflectivity spectra of HgSe and HgSeS are measured and analysed. The results suggest the one-mode behavior of phonon excitations in HgSeS mixed crystals.
12
Content available remote

Spin-Lattice Relaxation Beyond the Debye Approximation

39%
Witowski A., Bardyszewski W., Kutter C., Wyder P., Witkowska B., Mycielski A.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
533-535
EN
In this paper we present the results of magnetization relaxation in HgCdMnTe at high magnetic fields. In this mixed crystal the TA phonons have an energy lower than the spin splitting of the Mn^{2+} ground orbital singlet at about 20 T, which allows to check the effect of phonons with wave vectors from the edges of the Brillouin zone on the spin-lattice relaxation.
13
Publication available in full text mode
Content available

Infrared Spectroscopy of GaAs Doped with Mn

33%
Rutkowska A., Wasik D., Witowski A., Sadowski M., Orłowski W., Strzelecka G., Hruban A., Kamińska M., Twardowski A., Potemski M.
Acta Physica Polonica A
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2005
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vol. 108
|
issue 5
845-849
EN
We found that the fine structure related to Lyman spectra of [Mn^{2+}(d^5) + a hole] centers in GaAs was present only for samples with low Mn concentration. Such samples, at low temperature, did not show any hopping conductance within Mn impurity band. Magnetooptical measurements revealed that magnetic field induced splitting of the Lyman optical transitions was larger than Zeeman splitting observed for typical shallow acceptors in GaAs, like Be, Zn, and C. This experimental result proved that in the case of Mn acceptor impurity, the exchange coupling of a hole and the S = 5/2 Mn^{2+}(d^5) core could not be neglected, which was in accordance with the [Mn^{2+}(d^5) + a hole] model of the neutral Mn center in GaAs.
14
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Structural and Electronic Properties of Graphene Oxide and Reduced Graphene Oxide Papers Prepared by High Pressure and High Temperature Treatment

33%
Tokarczyk M., Kowalski G., Witowski A., Koziński R., Librant K., Aksienionek M., Lipińska L., Ciepielewski P.
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vol. 126
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issue 5
1190-1194
EN
"Graphene paper" prepared by new proprietary method involving high pressure and high temperature treatment in the reduction process show new possibilities in this area. Different phase content: multilayer and single layer graphene stacks recorded in this study for RGO samples are accompanied by the specific electric and optical parameters. We have found that process temperatures above 900°C play crucial role in structural and other properties. For the process temperature around 2000°C we found the onset of the graphitization in the samples.
15
Publication available in full text mode
Content available

Formation of Mn-Related Defect Band in InP

27%
Macieja B., Korona K., Piersa M., Witowski A., Wasik D., Wysmołek A., Strzelecka G., Hruban A., Surma B., Palczewska M., Kamińska M., Twardowski A.
|
EN
Electron paramagnetic resonance, optical absorption, luminescence and electrical studies of InP highly doped with Mn were performed. Electron paramagnetic resonance revealed presence of manganese in Mn^{2+}(d^5) configuration. In optical absorption, systematic reduction of InP band gap was observed with increase in Mn content. This was correlated with increase in photoionization-type absorption band starting at 0.2 eV. Time-resolved photoluminescence measurements showed decrease in photoexcited carrier lifetime and shortening of donor-acceptor pair recombination time with increase in Mn content. Moreover, photoluminescence band was shifted to lower energies, similarly to optical band gap. In electrical transport two mechanisms of conductivity were observed. Valence band transport dominated at higher temperatures, above 160 K, and activation energy of free-hole concentration was determined as about 0.20 eV. At lower temperatures hopping conductivity, clearly related to Mn defect band, was present. All these results were consistent with assumption of creation of Mn-related defect-band at 0.2 eV above InP valence band. It was found that Mn centers responsible for this band were in configurations of either d^5 or d^5 plus a hole localized about 7Å around corresponding Mn core.
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