137 research outputs found
Magnetic behavior of spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, from heat capacity and ac susceptibility studies
Heat-capacity (C) and ac susceptibility measurements have been performed on
the spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, to establish their magnetic
behavior and to explore whether there are magnetic frustration effects due to
antiferromagnetic coupling of the chains arranged in a triangular fashion.
While the paramagnetic Curie temperatures have been known to be large with a
negative sign, as though antiferromagnetic interaction is very strong, the
results establish that (i) the former apparently undergoes inhomogeneous
magnetic ordering only around 15 K, however without spin-glass anomalies, and
(ii) the latter orders antiferromagnetically at a relatively low temperature
(17 K). Thus, the magnetic frustration manifests differently in these
compounds.Comment: J. Solid State Chemistry, in pres
Magnetic behaviour of quasi-one-dimensional oxides, CaCoMnO
The results of ac and dc magnetization and heat capacity measurements on the
oxides, CaCoMnO, forming in a KCdCl-derived
rhombohedral quasi-one-dimensional crystal structure, are reported. As far as
CaCoO is concerned, the results reveal truly complex nature of the
two magnetic transitions, identified to set in at 24 and 12 K in the previous
literature. However, partial replacement of Co by Mn apparently results in a
long magnetic ordering of an antiferromagnetic type (below 13 and 18 K for x=
0.0 and 0.25 respectively), instead of spin-glass freezing in spite of the fact
that there is Co-Mn disorder; in addition, interestingly there are hysteretic
spin reorientation effects as revealed by isothermal magnetization behavior
Studies on La2-xPrxCayBa2Cu4+yOz (0.1 < x < 0.5) type mixed oxide superconductors
The La2-xPrxCayBa2Cu4+yOz (LaPrCaBCO) mixed oxides have been studied for
their structural and superconducting properties using X-ray diffraction (XRD),
d. c. resistivity, d. c. susceptibility and iodometric double titration. All
the LaPrCaBCO samples for x = 0.1 - 0.5, exhibit tetragonal crystalline
structure with P 4/mmm space group as determined by Rietveld analysis of the
X-ray diffraction data. With increasing x, enhancement in Tc is observed, which
is quite interesting for Pr substituted high Tc oxides. Maximum Tc ~ 58 K has
been observed for x = 0.5(La-2125 stoichiometry). The results of structural
studies and superconducting property measurements are presented in light of
increase in Tc in LaPrCaBCO system with increasing Pr concentration.Comment: 6 pages including 5 figures and 1 tabl
Low temperature magnetic studies on PbFe0.5Nb 0.5O3 multiferroic
PbFe0.5Nb0.5O3 (PFN), a well-known A(B′1/2B″1/2)O3 type multiferroic, was successfully synthesized in single phase by a single step solid state reaction method. The single phase PFN was characterized through XRD, microstructure through SEM, and magnetic studies were carried out through a temperature dependent vibrating sample magnetometer (VSM) and neutron diffraction (ND) measurements. PFN exhibits a cusp at around 150 K in the temperature dependent magnetic susceptibility corresponding to the Néel temperature (TN1) and another peak around 10 K (TN2) corresponding to spin-glass like transition. In the temperature dependent ND studies, a magnetic Bragg peak appears at Q=1.35 Å−1 (where Q=4πsinθ/λ, is called the scattering vector) below TN (150 K) implying antiferromagnetic (AFM) ordering in the system. On the basis of Rietveld analysis of the ND data at T=2 K, the magnetic structure of PFN could be explained by a G-type antiferromagnetic structure
Critical current density and flux pinning in La2-xPrxCa2xBa2Cu4+2xOz (x = 0.1 - 0.5) superconductors
Polycrystalline La2-xPrxCa2xBa2Cu4+2xOz (LPCaBCO) compounds with x = 0.1 -
0.5 were synthesized by solid-state reaction method and studied by room
temperature X-ray diffraction, dc resistivity, dc magnetization and iodometry.
The superconducting transition temperatures in these tetragonal triple
perovskite compounds increases from 32 to 62 K (Tconset values) with increasing
dopant concentration. The mixing of rare earth La3+ and Pr3+/4+ ions at rare
earth site (La3+) along with substitution of divalent Ca2+ results in the
shrinkage of unit cell volume. The contraction of unit cell volume due to
larger ion being substituted by smaller ions, gives rise to creation of pinning
centers in the unit cell leading to increase in critical current density and
flux pinningComment: To be published in Solid State Communications (2004
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