Magnetic ordering in the spin-ice candidate Ho2Ru2O7

Neutron scattering measurements on the spin-ice candidate material Ho2Ru2O7 have revealed two magnetic transitions at Tsimilar to95 and similar to1.4 K to long-range ordered states involving the Ru and Ho sublattices, respectively. Between these transitions, the Ho3+ moments form short-ranged ordered spin clusters. The internal field provided by the ordered S=1 Ru4+ moments disrupts the fragile spin-ice state and drives the Ho3+ moments to order. We have directly measured a slight shift in the Ho3+ crystal field levels at 95 K from the Ru ordering

Low-Temperature Continuous Flow Synthesis of Metal Ammonium Phosphates

The synthesis of the high performance inorganic materials essential to the quality of modern day life is hindered by traditionalist attitudes and reliance on outdated methods such as batch syntheses. While continuous flow methods have been extensively adopted in pharmaceutical circles, they remain largely unexplored for the preparation of inorganic compounds, despite higher efficiency, safety and versatility. In this publication, we demonstrate a step-change for the synthesis of metal ammonium phosphates through conversion of the extant batch process to a low-temperature continuous regime, exhibiting a tenfold increase in throughput combined with a significant decrease in particle size

Identifying the local structural units in La0.5Ba0.5MnO2.5 and BaY0.25Fe0.75O2.5 through the neutron pair distribution function

Neutron pair distribution function data are used to investigate the local structures of two oxygen deficient perovskites with simple cubic crystal structures. La0.5Ba0.5MnO2.5 is found to have alternating layers of MnO6 octahedra and MnO4 tetrahedra, making it similar to other members of the La1-xBaxMnO2.5 series with smaller x values which have brownmillerite crystal structures. Our fitting results suggest that La0.5Ba0.5MnO2.5 is not locally similar to any one brownmillerite structure type but instead has a variety of intra-layer and inter-layer relationships. We propose that this could be due to short range segregation of the much differently sized La(3+) and Ba(2+) cations, which creates significantly different inter-layer distances. BaY0.25Fe0.75O2.5 is found not to have a brownmillerite-type local structure but rather seems to consist of structural units which are similar to Ba3YFe2O7.5, an earlier member of the BanYFen-1O2.5n series. The PDF analysis shows that there are never neighboring Y atoms and that the O vacancies lie exclusively between Fe atoms, such that Y is always octahedrally coordinated. The PDF also suggests that there are more tetrahedral Fe than expected, which could be due to the presence of terminal O atoms in Fe centered dimeric units, similar to what is found in Ba3YFe2O7.5

Identifying the local structural units in La0.5Ba0.5MnO2.5 and BaY0.25Fe0.75O2.5 through the neutron pair distribution function

Neutron pair distribution function data are used to investigate the local structures of two oxygen deficient perovskites with simple cubic crystal structures. La0.5Ba0.5MnO2.5 is found to have alternating layers of MnO6 octahedra and MnO4 tetrahedra, making it similar to other members of the La1-xBaxMnO2.5 series with smaller x values which have brownmillerite crystal structures. Our fitting results suggest that La0.5Ba0.5MnO2.5 is not locally similar to any one brownmillerite structure type but instead has a variety of intra-layer and inter-layer relationships. We propose that this could be due to short range segregation of the much differently sized La(3+) and Ba(2+) cations, which creates significantly different inter-layer distances. BaY0.25Fe0.75O2.5 is found not to have a brownmillerite-type local structure but rather seems to consist of structural units which are similar to Ba3YFe2O7.5, an earlier member of the BanYFen-1O2.5n series. The PDF analysis shows that there are never neighboring Y atoms and that the O vacancies lie exclusively between Fe atoms, such that Y is always octahedrally coordinated. The PDF also suggests that there are more tetrahedral Fe than expected, which could be due to the presence of terminal O atoms in Fe centered dimeric units, similar to what is found in Ba3YFe2O7.5

High-resolution neutron scattering study of Tb2Mo2O7: A geometrically frustrated spin glass

The low-temperature magnetic properties of Tb2 Mo2 O7 have been studied with bulk susceptibility measurements and with elastic and high-resolution inelastic neutron scattering. This system is a spin glass with a freezing temperature Tg ∼25 K. A reverse Monte Carlo simulation of the neutron diffraction data shows weak ferromagnetic near-neighbor spatial correlations that do not extend beyond 10 Å. Neutron measurements of the spin dynamics reveal a slowing down with decreasing temperature without an anomaly at the glass transition. A low-lying Q -independent mode is seen at ω0 ∼0.28 meV. This dispersionless crystal electric field transition is measurable up to 60 K. © 2010 The American Physical Society

Thermal ring-opening polymerization of hydrocarbon-bridged [2]ferrocenophanes: Synthesis and properties of poly(ferrocenylethylene)s and their charge-transfer polymer salts with tetracyanoethylene

The poly(ferrocenylethylene)s [Fe(η-C5H3RCH2)2](n) 5a and 5b (a: R = H, b: R = Me) have been prepared by thermal ring-opening polymerization of the corresponding strained hydrocarbon-bridged [2]ferrocenophanes [Fe(η-C5-H3RCH2)2] (4a and 4b). An X-ray diffraction study of 4a indicated significant strain. Polymer 5a was crystalline and insoluble in common organic solvents and was characterized by solid-state 13C NMR. Polymer 5b, which was soluble in organic solvents, was characterized by 1H and 13C NMR. UV/visible spectroscopy and elemental analysis. Its molecular weight distribution was bimodal (gel permeation chromatography: M(w) = 9.6 x 104, M(n) = 8.6 x 104 for the high molecular weight fraction. M(w) = 4.8 x 103, M(n) = 3.5 x 103 for the oligomeric fraction), suggesting two polymerization mechanisms. The UV/visible spectrum implied a localized structure for the polymer backbone. Cyclic voltammetry revealed that 5b undergoes two reversible oxidations in CH2Cl2 solution at -0.25 and -0.16 V. The redox coupling is indicative of only a small degree of interaction between the iron centres. Thermogravimetric analysis indicated that 5a and 5b are thermally stable to ca. 300-350°C under N2. At higher temperatures they yield ferromagnetic iron carbide ceramics 6a and 6b (ca. 50% and 32%, respectively, at 600°C) together with molecular depolymerization products. The reaction of 5b with tetracyanoethylene (TCNE) yielded insoluble and soluble oxidized products 11 and 12, which differed in the degree of oligomerization of the TCNE(x)/(y-) counterions. These products were characterized by IR, elemental analysis, ESR spectroscopy, and magnetic susceptibility measurements. The last revealed the presence of significant antiferromagnetic interactions in 12