Raman scattering study of delafossite magnetoelectric multiferroic compounds: CuFeO2 and CuCrO2

Ultrasonic velocity measurements on the magnetoelectric multiferroic compound CuFeO2 reveal that the antiferromagnetic transition observed at TN1 = 14 K might be induced by an R-3m -> C2/m pseudoproper ferroelastic transition (G. Quirion, M. J. Tagore, M. L. Plumer, O. A. Petrenko, Phys. Rev. B 77, 094111 (2008)). In that case, the group theory states that the order parameter associated with the structural transition must belong to a two dimensional irreducible representation Eg (x^2 - y^2, xy). Since this type of transition can be driven by a Raman Eg mode, we performed Raman scattering measurements on CuFeO2 between 5 K and 290 K. Considering that the isostructural multiferroic compound CuCrO2 might show similar structural deformations at the antiferromagnetic transition TN1 = 24.3 K, Raman measurements have also been performed for comparison. At ambient temperature, the Raman modes in CuFeO2 are observed at omega_Eg = 352 cm^-1 and omega_Ag = 692 cm^-1, while these modes are detected at omega_E_g = 457 cm^-1 and omega_Ag = 709 cm^-1 in CuCrO2. The analysis of the temperature dependence of modes shows that the frequency of all modes increases down to 5 K. This typical behavior can be attributed to anharmonic phonon-phonon interactions. These results clearly indicate that none of the Raman active modes observed in CuFeO2 and CuCrO2 drive the pseudoproper ferroelastic transition observed at the N\'eel temperature TN1. Finally, a broad band at about 550 cm^-1 observed in the magnetoelectric phase of CuCrO2 below TN2 could be attributed to a magnon mode.Comment: 11 pages, 5 figure

Finding a rare fossilized comb jelly reveals new gaps in the fossil record

They look like jellyfish but they aren’t. They seem inoffensive but are efficient predators — occasionally, they even eat fish. They are gelatinous and very delicate — and extremely rarely do they fossilize! Ctenophores, also known as comb jellies, are colourful, translucent animals, that drift through oceanic waters. Unlike jellyfish, ctenophores don’t have stinging cells, and typically capture prey using long, sticky tentacles. Our research describing a fossilized ctenophore from Eastern Canada, published recently in Scientific Reports, suggests that our creature was a very late survivor from the very dawn of animals. It also means that a very controversial idea about early animal evolution can’t be rejected by the fossil record

Psychological mindedness and abstract reasoning in late childhood and adolescence: An exploration using new instruments

This study introduces two new measures of psychological mindedness, applying them in a study of the growth of abstract thinking in children and adolescents in a developmental design. The capacity to achieve psychological understanding of the self and of others involves comprehension of the motives, attitudes, and characteristics of the self and others. Psychological mindedness toward the self (PS) and toward others (PO) may be seen as complex cognitive capacities that should show a pattern of related development in childhood. Three groups of 60 fifth, eighth, and twelfth graders completed two measures of formal operations and two instruments to assess the two components of psychological mindedness. We find that psychological mindedness and abstract thinking both increase significantly with age, although the relationship between them is complex and varies with gender and age. Because the development of abstract reasoning skills does not correlate with the development of psychological mindedness in a simple way, a more complex model is necessary, taking age and gender differences into account. Performance on the two measures of psychological mindedness is found to be largely unrelated, suggesting that these are two different psychological skills. Implications of these findings are discussed, with special reference to education, peer counseling, and psychotherapy .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45274/1/10964_2005_Article_BF01537075.pd