Izabela Jendrzejewska

Influence of nickel substitution on the crystal structure of CuCr2Se4

Abstract Substitution of divalent nickel ions in the spinel structure of CuCr 2 Se 4 results in fundamental changes of the crystal structure from cubic to monoclinic symmetry. The investigations were conducted in the two systems: Cu 1− x Ni x Cr 2 Se 4 (for x =0.1–0.9) and CuCr 2− x Ni x Se 4 (for x =0.1–2.0). When copper was substituted with nickel, a change in crystal structure was observed as the amount of doped nickel (from spinel-type structure to Cr 3 S 4 -type structure) was increased. When chromium was substituted with nickel, no change in crystal structure was observed. For x =0.1–0.9 just the spinel phase exists. For x ≥1.0 the single-phase CuCr 2− x Ni x Se 4 compounds do not exist.

Influence of nickel substitution on the cation distribution and magnetic properties of ZnCr2Se4

Abstract Single crystals of ZnCr2Se4 spinel doped with nickel were prepared by chemical vapour transport in closed silica tubes using ZnSe and NiSe with CrCl3 as the transport agent. The chemical compositions of three crystals have been determined by X-ray diffraction for the system Zn–Ni–Cr–Se to determine the cation distribution and to study an influence of the Ni ions on the magnetic properties of the system. Based on the structural data the formula describing cation distribution in the system is: Zn[Cr2−xNix]Se4. For x values equal to 0.03, 0.05 and 0.10, the observed symmetry was cubic, space group Fd-3m. The site occupation factors resulting from the structure refinement showed Ni2+ substituted for the Cr3+ ions on octahedral sites. The experimental data for the saturation magnetization on the concentration of nickel in the external magnetic fields have been analyzed. The nickel substitution modified the saturation magnetic moments, which decrease with increasing Ni concentration (comparatively to the parent ZnCr2Se4).

Zur Kenntnis von Spinelltyp Mischkristallen CuxInyCr2Se4

Abstract Solid solutions in the system CuxInyCr2Se4 were obtained from the elements by the ceramic method at 800°C. They were examined by X-ray diffraction. The changes in the values of the lattice constants (CuCr2Se4, a = 10.335 A ; Cu0.2In0.8Cr2Se4, a = 10.716 A ) in samples with the compositions CuxIn0.33(2-x)Cr2Se4, CuxIn0.67(1-x)Cr2Se4 and CuxIn(1-x)Cr2Se4 respectively are discussed as well as the influence of the indium amount on the variation in the copper valence in CuCr2Se4.

X-Ray Investigations and Magnetic Properties of CuCr2-xSnxSe4 - Compounds

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.

Influence of Manganese and Tin Substitution on the Structure and Magnetic Properties of CdCr2Se4

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.

The single crystals Cu1 − xZnxCr2Se4

Abstract Octahedral crystals of Cu 1 − x Zn x Cr 2 Se 4 ( x = 0.1–0.9) up to 4 mm long were grown by the chemical transport method in a closed tube using CuSe, ZnSe and CrCl 3 . The lattice parameters of the crystals were determined by the Bond method. The semimicro quantitative X-ray fluorescence solution method was used to verify the chemical composition.

Growth and Structure of Zn1-xMnxCr2Se4 Single Crystals

The single crystals of ZnCr2Se4 spinel doped with manganese were prepared by the chemical vapour transport in closed silica tubes using stoichiometric contents of ZnSe, MnSe and CrCl3 as the transporting agent. Chemical composition of four single crystals of Zn-Mn-Cr-Se system with different concentration of manganese was analyzed and confirmed by X-ray diffraction study. The structure refinements, taking into account site occupancy factors, indicated that Mn ion shared tetrahedral sites with Zn ion. Thus, the formula describing cation distribution in the system is: Zn1-xMnxCr2Se4. For all x values equal to 0.12, 0.13, 0.18 and 0.24, the observed symmetry was cubic, space group Fd 3m .

X-Ray Analysis of New Gadolinium Doped CuCr2Se4

Abstract. Phase and structure analysis of CuCr2-xGdxSe4 (x=0.1÷0.3) synthesized using a solid state reaction method were carried out using X-Ray powder diffraction. All obtained compounds were found to be multi phase with the spinel phase being dominant up to x=0.1, indicating low solubility limit of gadolinium. Two compounds CuCr1.95Gd0.05Se4 and CuCr1.9Gd0.1Se4,. were chosen for a detailed structure refinement.

X-ray analysis of the new ferrites CuCr2-xFexse4

The series of ferrites CuCr2-xFexSe4 (x=0.1uf0b80.5) 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.

The X-ray studies and magnetic properties of Co0.83Fe1.8Se4

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.