R. L. de Almeida

Magnetic phase evolution in the LaMn1−xFexO3+y system

We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn1−xFexO3+y, in the whole range 0.0≤x≤1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn–Teller distortion, thus favoring a ferromagnetic (FM) superexchange interaction between Mn3+–O–Mn3+. For x=0.0 the oxygen excess (y≈0.09) produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn4+ ions and 82% of the usual Mn3+ ions, with possible double-exchange interaction between them. The Fe doping in this system is known to produce only stable Fe3+ ions. We find an evolution from a fairly strong FM phase with a Curie temperature TC∼160 K, for x=0.0, to an antiferromagnetic (AFM) phase with TN=790 K, for x=1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease (increase) in the FM (AFM) phase, accompanied by a systematic transiti...

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

Magnetic phase separation and cluster-spin-glass behavior in LaMn1−xFexO3+y

\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 the novel ruthenate La3.5Ru4O13: Possible mixed valence of Ru ions

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

TRIZ: criatividade como uma ciência exata?

({T}_{c})

Synthesis and magnetic properties of the double layer perovskite CeBaFe2O5+w

, 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

Synthesis and Characterization of BaFe2As2 Single Crystals Grown by In-flux Technique

{T}_{c}

Irreversibility lines and anomalous Meissner effect in Ba(Fe1-xCox)2As2 superconducting crystals

, 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.

Vortex matter behavior dependent on magnetic field orientation in Bi2Sr2CaCu2O8+δ crystals

The crystal structure and some magnetic properties were investigated for polycrystalline samples of LaMn1−xFexO3+y, prepared by solid-state reaction in air. All samples show the ORT-2 orthorhombic structure that suppresses the Jahn–Teller distortion and favors a ferromagnetic (FM) superexchange interaction between Mn3+–O–Mn3+. An evolution from a fairly strong FM phase, for x=0.0, to an antiferromagnetic (AFM) phase, for x=1.0, was observed. For intermediate Fe contents, a magnetic mixed-phase state occurs, with a gradual decrease (increase) in the FM (AFM) phase as x increases. A clear cluster-spin-glass (CG) behavior is observed in our samples for x≤0.1, where FM coupling dominates. In this case, the Vogel–Fulcher law describes very well the CG dynamics, giving reasonable values for the fitted parameters.

Magnetic phase separation in LaMn1-xFexO3+y

Structural, magnetization, heat capacity, and electrical resistivity measurements have been carried out on a new ruthenate compound La3.5Ru4O13. This compound forms in the orthorhombic structure (Pmmm space group, #47). The coexistence of the triple-layered perovskite-type planes [quasi-two-dimensional (2D) structure] and the rutilelike slabs [one-dimensional (1D) structure] leads to interesting magnetic and electronic properties in this compound. The relatively short Ru–O bond distances or stronger 4d-2p hybridization of rutilelike slabs suggest an electronic delocalization feature along the slab axis (b-axis). In the high-temperature region, a Curie–Weiss behavior of the magnetic susceptibility is observed with an effective magnetic moment μeff=(2.44±0.02)μB per Ru ion and a paramagnetic Curie temperature θp=−198±2 K. The magnetic susceptibility of this compound shows a peak at T∼47 K typical of an antiferromagnetic (AFM) order which is confirmed by heat capacity measurements. This AFM order can be asso...