Search

Half doped cluster glass compound Eu 0.5 Sr 0·5 CoO 3 is prepared in polycrystalline form and is characterized by using x-ray diffraction, x-ray absorption spectroscopy, x-ray photoelectron spectroscopy and magnetization studies. The magnetic properties of this compound have been reinvestigated using DC magnetization studies. Magnetization versus Temperature (M-T) measurements revealed that the sample is ferromagnetic below 110 K with an additional transition observed around 230 K, which has not been reported in the previous studies on this compound. After analyzing the 1/M versus temperature data, the new transition was attributed to the onset of short range ferromagnetic interactions in the sample at ~230 K. Based on magnetization versus applied magnetic field (M − H) measurement, the sample has been projected as a coexistent state of ferromagnetic and antiferromagnetic clusters below 110 K. In view of the coexistent magnetic state, the possibility of the presence of exchange bias in the system has also been explored and it was established that this compound exhibits a negative exchange bias of about −4683Oe, making it technologically important. [ABSTRACT FROM AUTHOR]

High pressure Raman spectroscopic studies on Polycrystalline CaCu 3 Ti 4 O 12 and SrCu 3 Ti 4 O 12 compounds are carried out in order to validate the theoretical predictions of a structural transformation near 3–4 GPa and an insulator to metal transition above 7 GPa [S. B. Fagan et al., Phys. Rev. B 72 , 014106 (2005)]. Our studies showed normal hardening and broadening of peaks with increasing pressure up to 20 GPa besides a discontinuity between 8 and 9 GPa which is attributed to an isostructural phase transition. The Ag(1) peak occurring at 442 cm −1 showed asymmetric Fano lineshape and the lineshape parameter ‘ q ’ shows an increase with increasing pressure. This is completely against the theoretical predictions of an insulator to metal transition above 7 GPa. [ABSTRACT FROM AUTHOR]

This is our first report highlighting the strain-disordered induced magnetic domain mapping in epitaxial thin films of SrRuO 3. Strain controls magnetic anisotropy and plays a crucial role in strong spin-phonon coupling. This study offers a way to induce complex coupling between the lattice degrees of freedom in this material, making it a promising candidate for potential spintronics-based applications. [Display omitted] • Temperature dependent magnetic force microscopy of SrRuO3 epitaxial thin films. • Visual evolution of magnetic domains across the two magnetic transitions. • Raman spectra showed strong spin-phonon coupling across magnetic ordering. • Perpendicular magnetic anisotropy is found dominating preferably in out-of-plane direction. • Magnetic order is strongly influenced by the lattice dynamics. SrRuO 3 epitaxial thin films with large strain disorder have been grown using pulsed laser deposition on (LaAlO 3) 0.3 (Sr 2 TaAlO 6) 0.7 (LSAT) and SrTiO 3 (STO) substrates. The films demonstrate two distinct transition temperatures in magnetic measurements. We present a visual evolution of magnetic domains across the two transitions using magnetic force microscopy in these films. The study clearly shows that the magnetic anisotropy corresponding to the two transitions is different. The perpendicular magnetic anisotropy is found dominating in films which results in domain spin orientation preferably in out-of-plane direction. The Raman study shows that the magnetic order strongly influences the lattice. The analysis of the phonon spectra around the magnetic transitions reveals the existence of strong spin-phonon coupling and the calculations resulted in the spin-phonon coupling constant λ ∼ 0.65 cm−1 and 1.96 cm−1, for SrRuO 3 films grown on LSAT and SrTiO 3 single crystal substrates, respectively. [ABSTRACT FROM AUTHOR]

This study sheds a light on the in-situ growth of nanoflakes structure in Bi 0. 9 La 0. 1 Fe 0. 5 Mn 0. 5 O 3 (BLFMO) thin film. The BLFMO thin films of various thicknesses were grown on LaNiO 3 (LNO) coated Si (100) substrates using pulsed laser deposition technique. A long-range crystal structure of the as prepared BLFMO thin films was studied by X-ray diffraction measurements, which shows that the LNO buffer layer allows growth for a specific orientation. The compact and densely packed nanoflake structures in BLFMO thin film samples were confirmed by surface morphological investigations. To measure the polarization versus electric field (p - E) loop of BLFMO chip samples, a standard bipolar sinusoidal waveform with its magnitude of 250 kV/cm was applied at the frequency of 1 kHz. The maximum saturation and remnant polarizations of 104.50 μC/cm2 and 86.24 μC/cm2 respectively were probed for a critical thickness (420 nm) of the BLFMO layer. The voltage polarity-dependent leakage current behavior of Ag/BLFMO/LNO thin-film capacitor is thoroughly explored in detail. The value of leakage current density was observed from 1.16 × 10−4 to 2.24 × 10−5 J/cm2 for BLFMO thin films at an external applied electric field of 300 kV/cm. The highest tunability ∼60.20% and minimum temperature capacitance coefficient ∼1.23 × 10−3 were also observed for the same critical thickness of proposed chip element. The present study may open up a new opportunity to fabricate thin film based ferroelectric memory devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The crystal and magnetic structure of brownmillerite Ca 2 Fe 2-x Al x O 5 ; x = 0.8 has been refined against the powder neutron diffraction data collected as a function of temperature from 3 K to 350 K. Ca 2 Fe 2-x Al x O 5 is a G-type antiferromagnet with Ibm 2 symmetry, the magnetic ion Fe occupies both tetrahedral and octahedral sites and both the sites are antiferromagnetically coupled individually. In this report, the mechanism of spin reorientation transition shown by these compounds is elucidated. The moment direction is found to be directed preferably along the crystallographic c -axis at low temperatures along with a small fraction of domains that are aligned along the a -axis. As the temperature is increased the domain with a -axis aligned moment inflates at the expense of domains with the moment directed along c -axis. However, at all temperatures both types of domains are found to be coexisting. The results suggest phase coexistence of the two magnetic structures with temperature dependent dynamics. [ABSTRACT FROM AUTHOR]

The phenomenon of relaxor ferroelectrics is studied through detailed Raman spectroscopy on polycrystalline Sr 1- x Pr x TiO 3 (x = 0.01–0.17) samples. The polar mode was observed up to very high temperature ~1000 K indicating presence of dipoles well above the characteristic relaxor temperatures and they develop a short range correlation at 505 K leading to formation of PNRs. Below 505 K, the TO 2 polar mode anomalously soften along with Fano resonance and changes in the octahedral tilt angle. This establishes growth of local polar order associated with local structural phase transition at T ~505 K. The local TiO 6 octahedral tilt scales with the intensity of the polar mode and hence can be used as an order parameter for relaxor transition. It is shown that the paraelectric to relaxor ferroelectric phase transition in this compound is random polarizability instability driven phenomenon which has been correlated with the local octahedral tilt angle. • The electric dipoles remains present well above the characteristic relaxor temperatures. • The local octahedral tilt angle modulates around 505K allowing growth of Polar nano regions (PNRs). • It is shown that the paraelectric to relax or ferroelectric phase transition in this compound is random polarizability instability driven phenomenon which has been correlated with the local octahedral tilt angle. [ABSTRACT FROM AUTHOR]