33 research outputs found
High temperature magnetic ordering in La2RuO5
Magnetic susceptibility, heat capacity and electrical resistivity
measurements have been carried out on a new ruthenate, La2RuO5 (monoclinic,
space group P21/c) which reveal that this compound is a magnetic semiconductor
with a high magnetic ordering temperature of 170K. The entropy associated with
the magnetic transition is 8.3 J/mole-K -close to that expected for the low
spin (S=1) state of Ru4+ ions. The low temperatures specific heat coefficient g
is found to be nearly zero consistent with the semiconducting nature of the
compound. The magnetic ordering temperature of La2RuO5 is comparable to the
highest known Curie temperature of another ruthenate, namely, metallic SrRuO3,
and in both these compounds the nominal charge state of Ru is 4+.Comment: 16 pages, 6 figures, To be published in Solid State Communication
Magnetic and transport properties of Mo substituted La0.67Ba0.33Mn1-xMoxO3 perovskite system
The effect of doping Mo for Mn on the magnetic and transport properties of
the colossal magnetoresistance material, La0.67Ba0.33MnO3, has been studied.
Compounds of the series La0.67Ba0.33Mn1-xMoxO3 (x=0.0 to 0.1) have been
prepared and found to crystallize in the orthorhombic structure (space group
Pbnm). Energy Dispersive X-ray Analysis (EDAX) measurements confirm the
stoichiometry of all the samples. Magnetotransport and magnetization
measurements reveal that the metal-insulator transition temperature (Tp)
decreases from 330K for x=0 to 255K for x=0.1. The change in Tp on Mo
substitution is relatively much smaller than the corresponding change observed
on substitution by other transition elements, such as Ti, Fe, Co, Ni, etc.
Further, the ferromagnetic transition temperature (TC) is nearly unchanged by
Mo substitution. This is in striking contrast to the large decrease in TC
observed with substitution of above-mentioned 3d elements. These unusual
magnetic and transport properties of La0.67Ba0.33Mn1-xMoxO3 may be either due
to the formation of magnetic pair between Mn and Mo or due to strong
Mo(4d)-O(2p) overlap, which in turn, may affect the Mn-Mn interaction via the
oxygen atomsComment: 25 pages, 5 figure
Physicochemical Characterization, and Relaxometry Studies of Micro-Graphite Oxide, Graphene Nanoplatelets, and Nanoribbons
The chemistry of high-performance magnetic resonance imaging contrast agents remains an active area of research. In this work, we demonstrate that the potassium permanganate-based oxidative chemical procedures used to synthesize graphite oxide or graphene nanoparticles leads to the confinement (intercalation) of trace amounts of Mn2+ ions between the graphene sheets, and that these manganese intercalated graphitic and graphene structures show disparate structural, chemical and magnetic properties, and high relaxivity (up to 2 order) and distinctly different nuclear magnetic resonance dispersion profiles compared to paramagnetic chelate compounds. The results taken together with other published reports on confinement of paramagnetic metal ions within single-walled carbon nanotubes (a rolled up graphene sheet) show that confinement (encapsulation or intercalation) of paramagnetic metal ions within graphene sheets, and not the size, shape or architecture of the graphitic carbon particles is the key determinant for increasing relaxivity, and thus, identifies nano confinement of paramagnetic ions as novel general strategy to develop paramagnetic metal-ion graphitic-carbon complexes as high relaxivity MRI contrast agents
Consequences of niobium doping for the ferromagnetism and microstructure of anatase Co:TiO2 films
Electrical properties of epitaxial junctions between Nb:SrTiO<SUB>3</SUB> and optimally doped, underdoped, and Zn-doped YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-δ</SUB>
Epitaxial thin films of optimally doped, underdoped, and Zn-doped YBa2Cu3O7-δ (YBCO) were grown on single crystal (001) Nb:SrTiO3 substrates by pulsed laser deposition (PLD) and the electrical properties of the corresponding interface junctions were examined. The growth conditions were optimized in each case to get the appropriate crystalline quality of the films as well as the desired normal state and superconducting properties. The films or heterointerfaces were characterized by x-ray diffraction, Rutherford backscattering (RBS) ion channeling spectrometry in normal and oxygen resonance modes, magnetic susceptibility, four probe in-plane resistivity, and the temperature dependent current-voltage (I-V) characteristics. Nonlinear I-V curves (forward and reverse) were obtained in all the cases, revealing some characteristic differences and interesting temperature evolution. These data, when analyzed within the framework of a standard description of transport across the metal-semiconductor (Schottky) interface, suggest lateral intrinsic nanoscale electrical inhomogeneity in the system. Also as compared to the case of optimally doped YBCO a small but definitive lowering of the effective Schottky barrier height ΦB is observed for junctions based on oxygen underdoped and Zn-doped YBCO