19 research outputs found
High temperature behavior of Sr-doped layered cobaltites Y(Ba1-xSrx)Co2O5.5: phase stability and structural properties
In this article we present a neutron diffraction in-situ study of the thermal
evolution and high-temperature structure of layered cobaltites Y(Ba, Sr)Co2
O5+{\delta}. Neutron thermodiffractograms and magnetic susceptibility
measurements are reported in the temperature range 20 K <= T <= 570 K, as well
as high resolution neutron diffraction experiments at selected temperatures.
Starting from the as-synthesized samples with {\delta} ~ 0.5, we show that the
room temperature phases remain stable up to 550 K, where they start loosing
oxygen and transform to a vacancy-disordered "112" structure with tetragonal
symmetry. Our results also show how the so-called "122" structure can be
stabilized at high temperature (around 450 K) in a sample in which the addition
of Sr at the Ba site had suppressed its formation. In addition, we present the
structural and magnetic properties of the resulting samples with a new oxygen
content {\delta} ~ 0.25 in the temperature range 20 K <= T <= 300 K
Brillouin scattering studies in FeO across the Verwey transition
Brillouin scattering studies have been carried out on high quality single
crystals of FeO with [100] and [110] faces in the temperature range of
300 to 30 K. The room temperature spectrum shows a surface Rayleigh wave (SRW)
mode at 8 GHz and a longitudinal acoustic (LA) mode at 60 GHz. The SRW mode
frequency shows a minimum at the Verwey transition temperature of 123 K.
The softening of the SRW mode frequency from about 250 K to can be
quantitatively understood as a result of a decrease in the shear elastic
constant C, arising from the coupling of shear strain to charge
fluctuations. On the other hand, the LA mode frequency does not show any
significant change around , but shows a large change in its intensity. The
latter shows a maximum at around 120 K in the cooling run and at 165 K in the
heating run, exhibiting a large hysteresis of 45 K. This significant change in
intensity may be related to the presence of stress-induced ordering of
Fe and Fe at the octahedral sites, as well as to stress-induced
domain wall motion.Comment: 14 pages, 3 figures, accepted in Physical Review B 200
A comparative study of magnetic and dielectric behaviors for La 1-xBi xMn 1-yFe yO 3 series (with x=0.5, 0.7 and y=0.3, 0.7)
10.1088/0953-8984/24/25/255902Journal of Physics Condensed Matter2425-JCOM
Heat capacity, thermopower and magnetoresistance effects in multiferroic La0.5Bi0.5Mn0.5Fe0.5O3
10.1007/s10853-013-7580-6Journal of Materials Science48217629-7634JMTS
A Brillouin study of the temperature-dependence of the acoustic modes across the insulator- metal transitions in V<SUB>2</SUB>O<SUB>3</SUB> and Cr-doped V<SUB>2</SUB>O<SUB>3</SUB>
Brillouin scattering studies have been carried out on high-quality single crystals of undoped and 0.9%
Cr-doped V2O3. The observed modes in both the samples at ~12 and ~60 GHz are associated with
the surface Rayleigh wave (SRW) and bulk acoustic wave (BAW), respectively. In the undoped sample, the mode
frequencies of the SRW and BAW modes decrease as the temperature is lowered from room temperature to the
insulator- metal transition temperature (TIM=TN=~130 K). Below the transition, the modes
show hardening. In the doped sample, the SRW mode shows a similar temperature-dependence as the undoped one, but
the BAW mode shows hardening from room temperature down to the lowest temperature (50 K). This is the first
measurement of the sound velocity below TIM in the V2O3 system. The softening of
the SRW frequency from 330 K to TIM can be qualitatively understood on the basis of the
temperature-dependence of C44, which, in turn, is related to the orbital fluctuations in the
paramagnetic metallic phase. The hardening of the mode frequencies below TIM suggests that
C44 must increase in the antiferromagnetic insulating phase, possibly due to the orbital
ordering
Entanglement of cation ordering and manipulation of the magnetic properties through a temperature-controlled topotactic interface reaction in nanocomposite perovskite oxides
International audienceSchematic view of cation ordering across the interface of the grain boundary of two different perovskites via controlled thermal treatment. Such ordering is sensitive to the magnetic property