Magnetic Structures of High Temperature Phases of TbBaCo2O5.5

Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite TbBaCo2O5.5 in the temperature range of 7-370 K. There have been observed several magnetic or structural transitions. Among these, the existence of the transitions to the insulating phase from the metallic one at ~340 K, to the one with the ferromagnetic moment at ~280 K and possibly to the antiferromagnetic one at ~260 K, with decreasing temperature T correspond to those reported in former works. We have studied the magnetic structures at 270 K and 250 K and found that all Co3+ ions of the CoO6 octahedra are in the low spin state and those of the CoO5 pyramids carry spins which are possibly in the intermediate spin state. Non-collinear magnetic structures are proposed at these temperatures. Two other transitions have also been observed at the temperatures, ~100 K and ~250 K.Comment: 9 pages, 2 tables, 10 figure

Transport and Magnetic Properties of R1-xAxCoO3 (R=La, Pr and Nd; A=Ba, Sr and Ca)

Transport and magnetic measurements have been carried out on perovskite Co-oxides R1-xAxCoO3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0<x<0.5: All sets of the R and A species except Nd1-xBaxCoO3 have been studied.). With increasing the Sr- or Ba-concentration x, the system becomes metallic ferromagnet with rather large magnetic moments. For R=Pr and Nd and A=Ca, the system approaches the metal- insulator phase boundary but does not become metallic. The magnetic moments of the Ca-doped systems measured with the magnetic field H=0.1 T are much smaller than those of the Ba- and Sr-doped systems. The thermoelectric powers of the Ba- and Sr-doped systems decrease from large positive values of lightly doped samples to negative ones with increasing doping level, while those of Ca-doped systems remain positive. These results can be understood by considering the relationship between the average ionic radius of R1-xAx and the energy difference between the low spin and intermediate spin states. We have found the resistivity-anomaly in the measurements of Pr1-xCaxCoO3 under pressure in the wide region of x, which indicates the existence of a phase transition different from the one reported in the very restricted region of x~0.5 at ambient pressure [Tsubouchi et al. Phys. Rev. B 66 (2002) 052418.]. No indication of this kind of transition has been observed in other species of R.Comment: 9 pages, 8 figures. J. Phys. Soc. Jpn. 72 (2003) No.

3,3′Diindolylmethane Suppresses Vascular Smooth Muscle Cell Phenotypic Modulation and Inhibits Neointima Formation after Carotid Injury

3,3'Diindolylmethane (DIM), a natural phytochemical, has shown inhibitory effects on the growth and migration of a variety of cancer cells; however, whether DIM has similar effects on vascular smooth muscle cells (VSMCs) remains unknown. The purpose of this study was to assess the effects of DIM on the proliferation and migration of cultured VSMCs and neointima formation in a carotid injury model, as well as the related cell signaling mechanisms.DIM dose-dependently inhibited the platelet-derived growth factor (PDGF)-BB-induced proliferation of VSMCs without cell cytotoxicity. This inhibition was caused by a G0/G1 phase cell cycle arrest demonstrated by fluorescence-activated cell-sorting analysis. We also showed that DIM-induced growth inhibition was associated with the inhibition of the expression of cyclin D1 and cyclin-dependent kinase (CDK) 4/6 as well as an increase in p27(Kip1) levels in PDGF-stimulated VSMCs. Moreover, DIM was also found to modulate migration of VSMCs and smooth muscle-specific contractile marker expression. Mechanistically, DIM negatively modulated PDGF-BB-induced phosphorylation of PDGF-recptorβ (PDGF-Rβ) and the activities of downstream signaling molecules including Akt/glycogen synthase kinase(GSK)3β, extracellular signal-regulated kinase1/2 (ERK1/2), and signal transducers and activators of transcription 3 (STAT3). Our in vivo studies using a mouse carotid arterial injury model revealed that treatment with 150 mg/kg DIM resulted in significant reduction of the neointima/media ratio and proliferating cell nuclear antigen (PCNA)-positive cells, without affecting apoptosis of vascular cells and reendothelialization. Infiltration of inflammatory cells was also inhibited by DIM administration.These results demonstrate that DIM can suppress the phenotypic modulation of VSMCs and neointima hyperplasia after vascular injury. These beneficial effects on VSMCs were at least partly mediated by the inhibition of PDGF-Rβ and the activities of downstream signaling pathways. The results suggest that DIM has the potential to be a candidate for the prevention of restenosis

Spin state equilibria and localized versus collective d-electron behaviour in neodymium and gadolinium trioxocobaltate(III)

Magnetic susceptibility measurements and mossbauer spectra show that NdCoO<SUB>3</SUB> and GdCoO<SUB>3</SUB> contain predominantly low-spin Co<SUP>III</SUP> ions at low temperatures which transform partially to high-spin Co<SUP>3+</SUP> until a certain temperature. Beyond this temperature, there is a transfer of e<SUB>g</SUB> electrons from Co<SUP>3+</SUP> to Co<SUP>III</SUP> giving rise to di- and tetra-valent Co species followed by short-range ordering. Co<SUP>3+</SUP> ions completely disappear at about 1000 K where there is a gradual transition from localized electron behaviour to collective behaviour. The cobaltates are semi-metals beyond this transition. The spin state equilibria and the electronic transition described here find support from electron transport properties, mossbauer parameters as well as differential thermal analysis and x-ray data

Mossbauer studies of the high-spin-low-spin equilibria and the localized-collective electron transition in LaCoO<SUB>3</SUB>

Mossbauer studies combined with magnetic-susceptibility data on well-characterized LaCoO<SUB>3</SUB> in the 4.2-1200-K region show that cobalt ions exist predominantly in the low-spin Co<SUP>III</SUP> state at low temperatures which transform partially to high-spin Co<SUP>3+</SUP> ions up to 200 K. Above 200 K, Co<SUP>3+</SUP> and Co<SUP>III</SUP> ion pairs transform to Co<SUP>II</SUP> and Co<SUP>4+</SUP> pairs. At high temperatures, the population of Co<SUP>3+</SUP> decreases significantly and completely disappears at the localized-electron-collective-electron transition temperature at 1210 K. The variations of the lamb-mossbauer factor and the center shift with temperature provide valuable information on the high-spin-low-spin equilibria, as well as on the nature of the phase transitions and symmetry changes in LaCoO<SUB>3</SUB>. All these changes are reflected in the transport properties of LaCoO<SUB>3</SUB>. There appears to be little doubt that the first-order localized-electron-collective-electron transition in LaCoO<SUB>3</SUB> is caused essentially by the change in entropy of the d electrons

Itinerant-electron ferromagnetism in La<SUB>1-x</SUB>Sr<SUB>x</SUB>CoO<SUB>3</SUB>: a Mossbauer study

Mossbauer and other studies establish that in La<SUB>1-x</SUB>Sr<SUB>x</SUB>CoO<SUB>3</SUB> (x&gt;0.125), ferromagnetic Sr<SUP>2+</SUP>-rich clusters coexist with paramagnetic La<SUP>3+</SUP>-rich regions in the same crystallographic phase, with the ferromagnetic component increasing with increasing x and decreasing T. The 3d holes created by Sr<SUP>2+</SUP> substitution are itinerant both above and below T<SUB>C</SUB>. All the experimental observations on this system can be explained on the basis of itinerant-electron ferromagnetism

Spin-state equilibria in holmium cobaltate

Mossbauer and magnetic susceptibility studies of HoCoO<SUB>3 </SUB>have shown that there is coexistence of low-spin Co(III) ions and high-spin Co<SUP>3+</SUP> ions; Co(III) being more predominant at low temperatures. The population of Co(III) and Co<SUP>3+</SUP> equalizes above a particular temperature with these ions occupying alternate oxygen octahedra, leading to an ordered phase. The ordering transition is evidenced by the temperature variation of Lamb-Mossbauer factor, x-ray Debye-Waller factor, and inverse susceptibility. Electrical-conductivity data reflect these changes in the spin-state equilibria and show that at around 1080 K, HoCoO3 becomes metallic. At this temperature, a first-order localized electron-collective electron transition seems to occur. Co(II) and Co<SUP>4+</SUP> are not formed by electron transfer from Co<SUP>3+</SUP> to Co(III) as in LaCoO<SUB>3</SUB>. This behavior is correlated with the variation of covalency in the cobaltates

Rare earth cobaltite catalysts: relation of activity to spin and valence states of cobalt

Catalytic activities of rare earth cobaltites and related compounds are shown to be related to the spin and valence states of cobalt

Localized-to-itinerant electron transitions in rare-earth cobaltates

Mossbauer studies show that cobalt ions in LaCoO<SUB>3</SUB> exist predominantly in the low-spin Co<SUP>III </SUP>state at low temperatures and partially transform to the high-spin Co<SUB>3+</SUB> state up to 200 K. Above 200 K, Co<SUP>II</SUP> and Co<SUP>4+</SUP> ions are formed by the transfer of d electrons from Co<SUP>3+</SUP> to Co<SUP>III</SUP>; Co<SUP>3+</SUP> ions completely disappear at the first-order localized-to-itinerant electron transition temperature