Papers by Author: Ewa Maciążek

Abstract: Abstract. The polycrystalline compounds in the ZnCr2-xNdxSe4 system were prepared by the ceramic method in closed silica tubes using ZnSe, Nd2Se3, and Cr2Se3 as starting materials. The chemical composition and structural data has been determined by X-ray diffraction. The observed symmetry is cubic, space group . For ZnCr1.95Nd0.05Se4 compounds, a pure spinel phase forms for stoichiometric and smaller amounts of ZnSe. For both compounds of ZnCr1.90Nd0.10Se4, near spinel phase, a foreign ZnSe phase exists. It may indicate that 10% doping is close to the solubility limit of Nd in ZnCr2Se4.

Abstract: A high spin (HS) – low spin (LS) transition has been discovered in the Co[Cr0.5Ga1.5]S4 spinel, where the Co ions occupy tetrahedral sites and the Cr and Ga ions octahedral ones. The latter are diluted by the non-magnetic Ga-ions. Application of magnetic fields revealed ferrimagnetic order with a Curie temperature TC = 126 K, a strong suppression of the magnetic susceptibility () and a slight shift of TC to lower temperatures. A cusp at 15.6 K on the ac (T) curve suggests a spin frustration of the re-entrant type. Characteristic for the HS-LS transition is an inflection point at 150 K on the 1/(T) curve, a lack of the Curie-Weiss region above TC and a small value of the magnetization, 4.76 emu/g at 4.4 K and at a magnetic field of 57.5 kOe.

Abstract: The series of ferrites CuCr2-xFexSe4 (x=0.10.5) were obtained as polycrystalline compounds using conventional ceramics sintering method. The stoichiometric amounts of spectrally pure elements were used for synthesis. The phase and structure determination was done using X-ray analysis. The Rietveld method was applied for structure refinement. It occurred that all samples were multi-phase, the main content crystallized in cubic, normal spinel structure.

Abstract: The polycrystalline Co0.83Fe1.8Se4 compound was obtained using ceramic method. The chemical composition was verified using energy-dispersive X-ray fluorescence spectrometry (EDXRF) and EDS method. X-ray analysis was used to make phase and structure analysis. The Rietveld method was applied for structure refinement. Co0.83Fe1.8Se4 compound crystallized in monoclinic system, space group C . The magnetic susceptibility and magnetization were measured, they revealed ferrimagnetic properties of a sample.

Abstract: We have observed that doping CuCr2Se4 with tin introduces and then increases the tetrahedral deformation of the spinel structure, which can be connected with the Jahn-Teller (JT) distortion due to Cr2+ ions in antiprismatic environment. The presence of Cr2+ is corroborated by the increase of the saturation magnetization above the 6μB value expected for the 2 Cr3+ ions. In the high limit of the high Sn doping the deformation is decreased, which we attribute to elimination of the JT condition by the increased local distortions. With the tin doping the magnetic structure evolves from the ferromagnet, through spin-glass like to the antiferromagnetic due to increased AF coupling in the system. This is corroborated by the decreasing transition temperature and the Curie-Weiss parameter.

Abstract: Single phase materials with general formula CdxMeyCr2Se4 (where Me = Mn, Sn) were obtained using solid state synthesis method. Both compounds are ferromagnets with TC =115K (Sn) and 135K (Mn). The values of Curie-Weiss parameter ΘC-W = 135K (Sn) and 145K (Mn) are higher than respective values of TC indicating a presence of competing antiferromagnetic component. The values of lattice parameters are consistent with Sn and Mn replacing Cd. Slight cadmium deficiency has been also observed.

Abstract: The polycrystalline compounds of the general formula Cd1-xNixCr2Se4 have been prepared by the ceramic method in closed silica tubes using CdSe, NiSe and Cr2Se3. The phase composition and structural data have been determined by X-ray diffraction. The observed symmetry is cubic, space group Fd 3m . Apart from spinel phases, other phases were observed: CdSe, NiSe2 and Cr5.6Se8. Depending on amount of nickel, nickel ions can occupy tetrahedral and octahedral sites.

Abstract: The polycrystalline Cd0.5Ge0.5Cr2Se4 and CdCr1.9Ge0.075Se4 compounds were obtained using ceramic method. X-ray analysis was used to make phase and structure analysis. The Rietveld method was applied for structure refinement. Both compounds crystallized in cubic, normal spinel structure, Fd 3m. Besides the main spinel phase, Cr2Se3 was observed.