C.A. Cardoso

Spin glass behavior in RuSr 2 Gd 1.5 Ce 0.5 Cu 2 O 10 − δ

The dynamics of the magnetic properties of polycrystalline RuSr 2 Gd 1 . 5 Ce 0 . 5 Cu 2 O 1 0 - δ (Ru-1222) have been studied by ac susceptibility and dc magnetization measurements, including relaxation and ageing studies. Ru-1222 is a reported magnetosuperconductor with Ru spins magnetic ordering at temperatures near 100 K and superconductivity in Cu-O 2 planes below T c ∼40 K. The exact nature of Ru spins magnetic ordering is still being debated, and no conclusion has been reached yet. In this work, a frequency-dependent cusp was observed in Χ a c vs T measurements, which is interpreted as a spin glass transition. The change in the cusp position with frequency follows the Vogel-Fulcher law, which is commonly accepted to describe a spin-glass with magnetically interacting clusters. Such an interpretation is supported by thermoremanent magnetization (TRM) measurements at T=60 K. TRM relaxations are well described by a stretched exponential relation, and present significant aging effects.

Synthesis of colloidal magnetite nanocrystals using high molecular weight solvent

In this work, we describe a single-step synthetic route to obtain magnetic nanocrystals (MN), Fe3O4 nanocrystals, soluble in different solvents. To synthesize grafted MN in a single step, we used a high molecular weight solvent (a polyol) that can be attached to the particle surface, which then transfers its solubility to the particle. Using polyols with different molecular weights and polarity enabled us to control the size, aggregation and morphology. The solubility behavior of the MN confirms our success in transferring the solubility of the adsorbed polymer to the nanocrystal.

Magnetic and superconducting properties of Ru Sr 2 Gd 1.5 Ce 0.5 Cu 2 O 10 − δ samples: Dependence on the oxygen content and aging effects

The magnetic and superconducting properties of

Synthesis, characterization, and magnetic properties of room-temperature nanofluid ferromagnetic graphite

\mathrm{Ru}{\mathrm{Sr}}_{2}{\mathrm{Gd}}_{1.5}{\mathrm{Ce}}_{0.5}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}

Physical properties of single-crystalline fibers of the colossal-magnetoresistance manganite La0.7Ca0.3MnO3

polycrystalline samples with different oxygen-doping levels are presented. A strong suppression of the superconducting temperature

Manifestation of finite temperature size effects in nanogranular magnetic graphite

({T}_{c})

Unusually strong coherent response from grain-boundary Josephson network in polycrystalline PrxY1 − xBa2Cu3O7 − δ

, as well as a reduction in the superconducting fraction, occurs as the oxygen content is reduced by annealing the samples in oxygen-deprived atmospheres. Drastic changes in the electrical resistivity are observed above

Superconducting and magnetic behaviour of niobium doped RuSr2Gd1.5Ce0.5Cu2O10−δ

{T}_{c}

Experimental and theoretical study of demagnetization fields in superconducting samples of orthorhombic shape

, possibly associated with oxygen removal, mainly from grain boundaries. However, the magnetic ordering is relatively less affected by the changes in oxygen content of the samples. The spin-glass transition is enhanced and shifted to higher temperatures with the reduction in oxygen content. This could be correlated with an increase in the spin disorder and frustration for the oxygen-depleted samples. Also, the same oxygen-vacancy-induced disorder could explain the reduction in the fraction of the sample showing antiferromagnetic order. We also report significant changes in the measured properties of the samples as a function of time.

Critical current density anisotropy of aligned MgB2 crystallites

We report the chemical synthesis route, structural characterization, and physical properties of nanofluid magnetic graphite (NFMG) obtained from the previously synthesized bulk organic magnetic graphite (MG) by stabilizing the aqueous ferrofluid suspension with an addition of active cationic surfactant. The measured magnetization-field hysteresis curves along with the temperature dependence of magnetization confirmed room-temperature ferromagnetism in both MG and NFMG samples.