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 Fe3_3O4_4 across the Verwey transition

Brillouin scattering studies have been carried out on high quality single crystals of Fe$_3$O$_4$ 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 $T_V$ of 123 K. The softening of the SRW mode frequency from about 250 K to $T_V$ can be quantitatively understood as a result of a decrease in the shear elastic constant C$_{44}$, 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 $T_V$, 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$^{3+}$ and Fe$^{2+}$ 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