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Magnetic Characteristics (magnetic + characteristic)
Selected AbstractsFerromagnetic nanoparticles embedded in self-arranged matricesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008K. Rumpf Abstract The investigated nanoscopic system, consisting of a non magnetic host material and precipitated ferromagnetic nanostructures shows a magnetic behaviour correlated to the size and shape of the deposited particles but also to their spatial distribution within the template which modifies the magnetic interactions between them. The nanostructures are deposited electrochemically into an etched silicon wafer exhibiting an array of channels of a few ten nanometers in diameter and a length up to 50 µm. The self-assembled grown templates offer the opportunity of tuning the magnetic properties by varying the geometrical characteristics of the membrane which can be loaded with different metals like Ni or Co with variable metal distribution. Magnetic characteristics like coercivity, magnetic anisotropy and temperature dependent magnetization give a survey about the structure and the magnetic interactions of the nanocomposite. This achieved ferromagnetic nanocomposite system is not only of interest for basic research but also gives rise to applications in magneto-optics, spintronics and sensor application. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Preparation and characterization of powders and crystals of Vn-xTixO2n-1 Magneli oxidesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10-11 2005D. Calestani Abstract Vn-xTixO2n-1 Magnéli phases have been synthesized under vacuum in powder form (n = 4, 0 , x , 0.4) and crystals (n = 4 and 5, x = 0.5 and 1.4, respectively), grown by chemical vapour transport in closed ampoules. TeCl4 and NH4Cl were used as transporting agents. Needle-shaped crystals as long as 200-300 micrometers or 2-3 mm were obtained when in presence of NH4Cl or TeCl4, respectively. The powder and crystal structures were examined by X-ray diffraction and the transport and magnetic characteristics were measured.. The powders resulted to be single-phase and the relevant composition was assumed to be equal to the nominal one. The overall stoichiometry of compounds, n, was determined from single crystal X-ray diffraction data. The Ti content, x, was deduced from the elementary cell volume, by applying the Végard law. Crystals were mainly untwinned and of good quality. The elementary cell of both, powders and crystals, was triclinic (P-1) and did not change with doping. DC electrical resistivity of the crystals was measured in a four-points (van der Pauw) configuration. DC magnetic susceptibility of the powders was measured in a SQUID magnetometer. The Ti doping was found to progressively smooth and finally to suppress the magnetic transitions occurring in the V4O7. The metal-insulator transitions observed in V4O7 and V5O9, at around 235 and 125 K respectively, were not observed in the doped crystals, thus indicating some significant change of the electronic structure of the V oxides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Geophysical identification of unmarked historic gravesGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2010Rinita A. Dalan Down-hole magnetic susceptibility techniques were explored as a means of improving near-surface geophysical surveys in historic grave detection. These techniques were used to document distinctive magnetic characteristics of grave shafts at three historic cemeteries first surveyed using various near-surface geophysical methods. Tests revealed a low magnetic susceptibility signature that soil magnetic studies indicated was largely related to differential soil compaction associated with the excavation and refilling of grave shafts. Most apparent at depths beyond those reached by soil penetrometers, this magnetic signature offers a way to assess anomalies identified by near-surface techniques that potentially represent graves. At one cemetery, magnetic studies of the interments themselves suggested spatially patterned, magnetically enhanced zones that might also aid in burial identification in certain contexts. While down-hole techniques will not be foolproof, they do provide another geophysical tool that can be used to improve grave detection. © 2010 Wiley Periodicals, Inc. [source] Porous silicon/metal nanocomposite with tailored magnetic propertiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Petra Granitzer Abstract Porous silicon (PS) templates in the meso/macro porous regime with oriented pores clearly separated from each other and filled in a galvanic deposition process with various metals, especially ferromagnetic ones are magnetically investigated. The employment of different metals (e.g. Ni, Co, NiCo) together with the variation of the electrochemical deposition parameters modifies the structural characteristics of the PS/metal nanocomposite and thus leads to distinct magnetic properties of the hybrid system. Furthermore the use of different PS-templates which means a change of the pore-diameter and interpore spacing results also in various magnetic characteristics, especially influences on the magnetic interactions among the deposited metal nanostructures. Therefore the specimens show tailored magnetic properties like coercivity, squareness and magnetic anisotropy. The achieved nanocomposite merges electronic properties of a semiconductor with nanomagnetism and therefore opens the possibility of integrated spin-based electronic devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis of MnGeO3 polycrystalline and single-crystal samples and comparative analysis of their magnetic propertiesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009N. V. Sapronova Abstract MnGeO3 single crystals have been grown by a flux method. The obtained MnGeO3 is orthorhombic; a Pbca space group does not undergo any structural phase transitions in the range from room temperature to 900 °C. Magnetic measurements carried out for the first time on the MnGeO3 single crystal have revealed higher values (TN = 38 K and , = ,100 K) as compared to the data for polycrystalline samples reported in the literature (TN = 10 K and 14 K, , = ,54 K and ,46 K). These magnetic parameters for polycrystalline samples synthesized by us are close to the literature data. A Mössbauer spectrum taken at T = 300 K for a sample containing 5% Fe257O3 shows that manganese ions, Mn2+, occupy two nonequivalent positions and iron is included in a sublattice as Fe2+ and distributed among two positions substituting Mn2+. In this study, the magnetic characteristics are shown to be sensitive even to minor impurity amounts. The MnGeO3 magnetic structure and one of possible reasons causing the effect of impurities on the MnGeO3 magnetic properties are considered in the framework of a simple indirect coupling model. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature dependence of a twofold magnetic behaviour of a nanoscopic metal/silicon hybrid system , a comparison between Ni/Si and Co/SiPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2009K. Rumpf Abstract The investigated hybrid nanocomposite consists of a porous silicon template with electrochemically embedded Ni or Co nanostructures and offers magnetic characteristics which can be tailored by the electrochemical process parameters during fabrication. A twofold magnetic behaviour can be observed, a first one due to the spinmagnetism at magnetic fields below the saturation magnetization of the deposited metals and a second non-saturating term at higher fields (> 1 T up to 7 T) above the saturation magnetization. In case of Ni deposited within the pores this non-saturating term shows a paramagnetic characteristic and follows exactly the Curie-Weiss law, whereas for Co/porous silicon samples the temperature dependent magnetization shows some deviations from the Curie Weiss law. In this high field region a difference in the temperature dependence between Ni and Co is observed whereas the non-saturating term does not depend on the geometry of the embedded nanostructures in contrast to the ferromagnetic behaviour at lower magnetic fields. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural and Magnetic Modulation of a Purely Organic Open Framework by Selective Guest InclusionCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007Daniel Maspoch Dr. Abstract Solvent inclusion/evacuation caused variations in the structural and magnetic characteristics of the purely organic porous magnet based on the tricarboxylic-substituted PTMTC radical. Whereas no inclusion is observed for nonpolar solvents, the exposure of crystals of the ,-phase of PTMTC to vapors of polar organic solvents with hydrogen acceptor and/or donor functionalities, such as, ethanol, benzoic alcohol, n -decanol, THF, and DMSO results in the inclusion of these solvents in the highly polar tubular channels of the ,-phase. The resulting inclusion compounds of formula PTMTC,x(guest) show several structural rearrangements, as confirmed by IR and XRPD (X-ray powder diffraction) measurements. The crystal transformations have been studied for a specific case: the PTMTC,EtOH adduct. The crystal structure reveals that included guest solvent molecules participate in the formation of new hydrogen bonds with the carboxylic groups of PTMTC radicals, inducing the disruption of several direct hydrogen bonds among these radicals. As expected, the interruption of direct hydrogen bonds between PTMTC radicals induces large transformations in the magnetic properties. From the ferromagnetic behavior of the ,-phase, predominant antiferromagnetic interactions are observed for the inclusion adducts. Interestingly, both structural and magnetic changes are reversible after removal of guest solvent molecules. [source] | ||||||||||