RESUMEN
Enhanced magnetic moment and coercivity in SrRuO3 thin films are significant issues for advanced technological usages and hence are researched extensively in recent times. Most of the previous reports on thin films with enhanced magnetic moment attributed it to the high spin state. Our magnetization results show high magnetic moment of 3.3 µB/Ru ion in the epitaxial thin films grown on LSAT substrate against 1.2 µB/Ru ion observed in bulk compound. Contrary to the previous reports the Ru ions are found to be in low spin state and the orbital moment is shown to be contributing significantly in the enhancement of magnetic moment. We employed x-ray absorption spectroscopy and resonant valance band spectroscopy to probe the spin state and orbital contributions in these films. The existence of strong spin-orbit coupling responsible for the de-quenching of the 4d orbitals is confirmed by the observation of the non-statistical large branching ratio at the Ru M2,3 absorption edges. X-ray magnetic circular dichroism studies performed at the Ru M2,3 edges provided direct evidence of significant contribution of orbital moment in the film grown on LSAT. The relaxation of orbital quenching by strain engineering provides a new tool for enhancing magnetic moment and strain disorder is shown to be an efficient mean to control the spin-orbit coupling.
RESUMEN
The short-range structure of 20BaO-80TeO2 glass was studied in situ by high pressure neutron diffraction and high pressure Raman spectroscopy. Neutron diffraction measurements were performed at the PEARL instrument of the ISIS spallation neutron source up to a maximum pressure of 9.0 ± 0.5 GPa. The diffraction data was analysed via reverse Monte Carlo simulations and the changes in the glass short-range structural properties, Ba-O, Te-O and O-O bond lengths and speciation were studied as a function of pressure. Te-O co-ordination increases from 3.51 ± 0.05 to 3.73 ± 0.05, Ba-O coordination from 6.24 ± 0.19 to 6.99 ± 0.34 and O-O coordination from 6.00 ± 0.05 to 6.69 ± 0.06 with an increase in pressure from ambient to 9.0 GPa. In situ high pressure Raman studies found that the ratio of intensities of the two bands at 668 cm-1 and 724 cm-1 increases from 0.99 to 1.18 on applying pressure up to 19.28 ± 0.01 GPa, and that these changes are due to the conversion of TeO3 into TeO4 structural units in the tellurite network. It is found that pressure causes densification of the tellurite network by the enhancement of co-ordination of cations, and an increase in distribution of Te-O and Ba-O bond lengths. The original glass structure is restored upon the release of pressure.
RESUMEN
The competition and cooperation between ferroelectric and anti-ferro-distortion (AFD) instabilities are studied using pressure dependent Raman spectroscopy on polycrystalline powder samples of Sr1-x Ca x TiO3(x = 0.0, 0.06, 0.25, 0.35). For x = 0.0 composition, a broad polar mode is detected in the Raman spectra above 6 GPa, while for x = 0.06 composition, the polar modes appear well above 9 GPa where the AFD modes showed strong suppression. In x = 0.25 and 0.35 composition, the application of small pressure resulted in the appearance of strong AFD modes suppressing the polar modes. At elevated pressures, re-entrant polar modes are observed along with the broad AFD modes and some new peaks are also observed, signifying the lowering of local symmetry. The reappearance of polar modes is found to be related to pressure induced symmetry disorder at local level, suggesting its electronic origin. The re-entrant polar modes observed at higher pressure values are found to be significantly broad and asymmetric in nature, signifying the development of ferroelectric micro regions/nano domains coexisting with AFD. The lower symmetry at local length scale provides a conducive atmosphere for coexisting AFD and FE instabilities.
