Papers by Keyword: Magnetic Ordering

Abstract: The normal state of high-T_c superconducting cuprates is crucial to understanding of the mechanism in superconductivity. There are two main ways to remove superconductivity so that the sample is in a normal state, that is by applying a large magnetic field or adding impurities such as Zn to the sample. To investigate the crystal structure and magnetic properties in the normal state of electron-doped high-T_c cuprates in overdoped regime, Eu_2-xCe_xCu_0.97Zn_0.03O_4+α-δ (ECCZO) with x = 0.16, 0.17, 0.18, and 0.19 has been synthesized by the solid-state reaction method. The crystal structure and magnetic properties of the samples were characterized by XRD and SQUID measurements. The results of XRD measurements shows all samples have T’-structure and the values of lattice parameters a, CuO bond length, and crystallite size increased with increasing x. On other hand, the value of lattice parameters c decreased with increasing x, causing the expansion of the tetragonal unit cell in the horizontal direction. From susceptibility measurements, in the normal state with 3% of Zn impurity all samples have the paramagnetic behaviour. The magnetic parameters of these samples analysed by the Curie law. With increasing of Ce concentration, the C and the are increased. The increase in the magnetic parameters since the increasing in magnetic ordering.

Abstract: We investigated the magnetic properties of pyrochlore ruthenates, R₂Ru₂O₇, by using the muon spin relaxation (μSR) method. The appearance of a magnetically ordered state was confirmed below 145 K by observing the decrease in the initial asymmetry of the muon-spin polarization. This was due to a long-range ordering of Ru⁴⁺ spins. An additional anomaly in the μSR time spectrum was observed around 30 K. A part of the lost initial asymmetry was recovered and gradually decreases again with decreasing temperature below 30 K. This anomaly was supposed to be due to a magnetic ordering of Nd³⁺ spins which was coupled with ordered Ir moment via the 3d-4f exchange interaction.

Abstract: Neutron diffraction has been carried out to study temperature evolution of crystal and magnetic structure parameters of the multiferroic (0.9)BiFeO₃ + (0.1)BaTiO₃ over region (300 – 1000) K. Crystal structure is rhombohedral over whole temperature region and it is described by the R3c space group. The lattice parameters increase with temperature. The Ba ions are placed in the Bi sublattice and the Ti ions partly occupy the Fe sublattice. Assuming that the sample has a modulated magnetic structure with the propagation vector k = [0.0045, 0.0045, 0], we obtained a temperature dependence of the Fe-ion magnetic moment. The value of the moment is equaled to be μ = (3.46 ± 0.05) μ_B at 300 K and becomes zero at 600 K.

Abstract: The results of the study of structures forming in magnetic colloids with magnetized aggregates under the action of an elliptically polarized rotating magnetic field are discussed. When a magnetic colloid layer with magnetized aggregates is affected by an elliptically polarized rotating magnetic field, some ordering of the structural lattice is observed, which is determined by the frequency and orientation of the rotating magnetic field polarization ellipse as well as by the value of an additionally imposed steady magnetic field.

Abstract: Six compositions: x = 0.0 to 0.5 of the spinel system Mn1.5(1-x)Ti0.5(1-x)Fe(1+ 1.5x) Li(0.5)x O4 are synthesized by ceramic method. The structural and magnetic properties are studied by means of X-ray diffraction, AC susceptibility, Magnetization and Mossbauer spectroscopy. The study reveals the significance of FeA-O-FeB magnetic linkages in evolution of long range magnetic ordering through rise in Curie temperature and growth of magnetic hyperfine field with increase in x.

Abstract: For the first time the rearrangement of cerium local environment in Ce2Fe17-xMnx(x = 0; 1; 2) intermetallics vs. Mn concentration and temperature was investigated by thespectroscopy of extended X-ray absorption fine structure (EXAFS) above K-Ce absorptionedge. At the same time under similar conditions by the spectroscopy of X-ray absorption near-edge structure (XANES) above L3-Ce absorption edge the valence state of Ce was studied. Thecorrelation is found between changes in local electronic and crystalline structure observed inCe2Fe17-xMnx and the types of magnetic states in these compounds.

Abstract: Conditions of coexistence of Fe/Cr/Fe film states with parallel and antiparallel Fe layer magnetisations orientation are established. The transition from antiparallel to parallel orientation in external magnetic field is caused with Cr layer spin density wave phase change when wave node in the centre of Cr layer is substituted with wave antinode. The coexistence of these two states means that Fe/Cr/Fe film ferromagnetic state created with external magnetic field retains after the switching this field off. This phenomenon will manifest itself in the fact that magnetisation curve of initially antiferromagnetic Fe/Cr/Fe film will go outside the hysteresis loop of it's remagnetisation in ferromagnetic state created by external field.

Abstract: Owing to the technological importance of M-type hexaferrites of general formula MFe12O19 (M = Ba, Sr and Pb) and their substituted analogues, a staggering number of research activities on their synthesis, magnetic properties and thermal properties are being pursued in recent years. However, many critical issues on the effect of aliovalent ion substitution either on the M-site or Fe-sites are still unexplored. This paper deals with a survey of crystallochemical and thermodynamic properties of this important class of ferrimagnetic oxides.

Abstract: The effect of hydrostatic argon pressure equal to 105 Pa and 1.1 GPa applied to processing at up to 1270 K (HT) of Si:Cr samples prepared by Cr+ implantation (dose 1x1015 cm-2, 200 keV) into (001) oriented Czochralski silicon, has been investigated by Secondary Ion Mass Spectrometry, photoluminescence, X-ray and SQUID methods. Cr+ implantation at this energy and dosage produces amorphous silicon (a-Si) near the implanted ions range. Solid phase epitaxial re-growth (SPER) of a-Si takes place at HT. The Cr profile does not depend markedly on HP applied during processing at 723 K. Si:Cr processed at up to 723 K indicates magnetic ordering. Annealing under 105 Pa at 873 K, 1070 K and 1270 K results in a marked diffusion of Cr toward the sample surface. In the case of processing under 1.1 GPa this diffusion is less pronounced, SPER of a-Si is retarded and the a-Si/Si interface becomes enriched with Cr. The Cr concentration in Si:Cr sample processed at 1270 K under 1.1 GPa forms two distinct maxima, the deeper one at 0.35 μm depth.

Abstract: The structure studies of single crystalline silicon implanted at 340 K or 610 K with Mn+ ions (Si:Mn) and subsequently processed under atmospheric and enhanced hydrostatic pressure at up to 1270 K are reported. The defect structure was determined by an analysis of X-ray diffuse scattering around the 004 reciprocal lattice point and by electron microscopy. High resolution X-ray diffraction techniques based on the conventional source of radiation were used for this purpose. The crystal structure of Si:Mn and the Si1-xMnx precipitates in the implantation – disturbed layer were studied by synchrotron radiation diffraction in the grazing incidence geometry. Processing of Si:Mn results in crystallization of amorphous Si within the buried implantation – disturbed layer and in formation of Mn4Si7 precipitates. Structural changes are dependent both on temperature of the Si substrate at implantation and on processing parameters.