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Electrical and Magnetic Studies of Zn_{x}Mn_{y}Cr_{z}Se_{4} p-Type Semiconductors

100%
Jendrzejewska I., Groń T., Duda H., Zajdel P., Pacyna A., Maciążek E.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
913-915
EN
The structural, electrical and magnetic investigations carried out on the Zn_{x}Mn_{y}Cr_{z}Se_{4} polycrystals with y = 0.19, 0.29 and 0.38 revealed the spinel structure with the Mn ions occupying tetrahedral sites, p-type conduction with polaronic transport at high temperatures and antiferromagnetic order with a Néel temperature of 20 K and a Curie-Weiss temperature of 103 K. With increasing Mn content in a sample both the effective magnetic moment and the re-entrant temperature increase while the first and second critical fields connected with a metamagnetic transition and the breakdown of the conical spin arrangement decrease, respectively. These results are interpreted in terms of giant cubic anisotropy as well as an effect of Mn impurities on the screw structure of ZnCr_{2}Se_{4}.
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The Mössbauer Spectroscopy and Analytical Investigations οf the Polycrystalline Compounds with General Formula Zn_xSn_yCr_zSe_4

100%
Jendrzejewska I., Hanc A., Zajdel P., Kita A., Goryczka T., Maciążek E., Mrzigod J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1591-1597
EN
We present combined X-ray powder diffraction and Mössbauer ^{119}Sn studies of polycrystalline compounds with a general formula Zn_xSn_yCr_zSe_4 (where x+y+z ≈3). The obtained single-phase compounds crystallize in the spinel cubic structure - Fd3m. Tin ions are found to occupy both tetrahedral and octahedral sublattices. On the contrary to the strong tetrahedral site preference energy of Sn, the presented data strongly suggest that the increase in lattice parameters with Sn doping is caused by Sn ions that incorporated into octahedral positions. A quadrupole and isomer shifts of ^{119}Sn in (SnSe_4)^{6-} and (SnSe_6)^{4-} are also reported.
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The Mössbauer and X-Ray Studies οf the Spinel Ferrites Cu_{0.5}Fe_{0.5}Cr_2Se_4 and Cu_{0.2}Fe_{0.8}Cr_2Se_4 Prepared by the Ceramic Method

100%
Maciążek E., Hanc A., Sitko R., Zawisza B., Jendrzejewska I., Mrzigod J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 6
1599-1603
EN
Seleno-spinels with nominal chemical composition Cu_{0.5}Fe_{0.5}Cr_2Se_4 and Cu_{0.2}Fe_{0.8}Cr_2Se_4 were prepared as polycrystalline samples using ceramic method. The assumed composition was verified by wavelength-dispersive X-ray fluorescence spectrometry. The X-ray analysis was carried out in order to make phase analysis and to compare its results with those obtained with the Mössbauer spectroscopy.
4
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Effect of Cation Substitution on Critical Fields in the n-type Zn_{x}Sn_{y}Cr_{z}Se_{4} Spinel Semiconductors

100%
Groń T., Jendrzejewska I., Maciążek E., Pacyna A., Duda H., Zajdel P., Krok-Kowalski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
971-974
EN
The ac dynamic magnetic susceptibility was used to study a cation substitution on critical fields in polycrystalline (Zn_{0.87}Sn_{0.048})Cr_{2.02}Se_{4} and Zn_{0.93}[Cr_{1.95}Sn_{0.05}]Se_{4} spinels with tetra- and octahedral coordination of Sn ions, respectively. An increasing static magnetic field shifts the Néel temperature T_{N} to lower temperatures while a susceptibility peak at T_{m} in the paramagnetic region - to higher temperatures. Below T_{N} the magnetic field dependence of susceptibility, χ_{ac}(H), shows two peaks at critical fields H_{c1} and H_{c2}. The values of H_{c1} decrease slightly with temperature while the values of H_{c2} decrease strongly with temperature, especially for spinel with octahedral coordination of Sn ions, suggesting a weakness of the ferromagnetic component.
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