1,048 research outputs found
Magnetic-history-dependent nanostructural and resistivity changes in Pr0.5Ca0.5Mn0.98Cr0.02O3
We show that nanostructure and resistivity of Pr0.5Ca0.5Mn0.98Cr0.02O3 are
sensitive to whether the sample is zero-field-cooled (ZFC) of field-cooled (FC)
either in the 'self magnetic field (H = 2 T)' of the electron microscope or
under the external magnetic field of 2 T. FC resistivity at H = 2 T is lower
than ZFC values below 140 K. The average value of the chare-orbital modulation
vector (q = 0.44) of the FC crystallites is lower than that of the ZFC
cystallites (q = 0.48) and the FC crystallites exhibit numerous defects like
discommensuration, dislocations and regios with loss of superstructures
compared to the ZFC crystallites.Comment: 7 pages, 3 figure
Electronic Correlations in CoO2, the Parent Compound of Triangular Cobaltates
A 59Co NMR study of CoO2, the x=0 end member of AxCoO2 (A = Na, Li...)
cobaltates, reveals a metallic ground state, though with clear signs of strong
electron correlations: low-energy spin fluctuations develop at wave vectors q
different from 0 and a crossover to a Fermi-liquid regime occurs below a
characteristic temperature T*~7 K. Despite some uncertainty over the exact
cobalt oxidation state n this material, the results show that electronic
correlations are revealed as x is reduced below 0.3. The data are consistent
with NaxCoO2 being close to the Mott transition in the x -> 0 limit.Comment: 4 pages, submitte
Magnetic structure and phase diagram in a spin-chain system: CaCoO
The low-temperature structure of the frustrated spin-chain compound
CaCoO is determined by the ground state of the 2D Ising model on
the triangular lattice. At high-temperatures it transforms to the honeycomb
magnetic structure. It is shown that the crossover between the two magnetic
structures at 12 K arises from the entropy accumulated in the disordered
chains. This interpretation is in an agreement with the experimental data.
General rules for for the phase diagram of frustrated Ising chain compounds are
formulated.Comment: 4 pages, 2 figure
Ferromagnetic to spin glass cross over in (La,Tb)_{2/3}Ca_{1/3}MnO_{3}
In the series La_{2/3-x}Tb_{x}Ca_{1/3}MnO_{3}, it is known that the
compositions are ferromagnetic for smaller values of x and show spin glass
characteristics at larger values of x. Our studies on the magnetic properties
of various compositions in the La_{2/3-x}Tb_{x}Ca_{1/3}MnO_{3} series show that
the cross over from ferromagnetic to spin glass region takes place above x ~
1/8. Also, a low temperature anomaly at 30 K, observed in the ac susceptibility
curves, disappears for compositions above this critical value of x. A mixed
phase region coexists in the narrow compositional range 0.1 <= x <= 0.125,
indicating that the ferromagnetic to spin glass cross over is not abrupt.Comment: 5 pages, 5 figure
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