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Muon spin depolarization has been studied in moderately concentrated AgMn and AuFe alloys from the freezing temperature T~up to 300 K. The muon depolarization function can be analyzed to show that the temperature dependence of the strongly nonexponential form of the local spin autocorrelation function in these canonical alloys is similar to that observed in numerical simulations on Ising spin glasses. The dynamic behavior above Tg appears to be an intrinsic precursor to spin glass freezing.

Modified iron phosphate glasses have been prepared with nominal molar compositions [(1−x)·(0.6P2O5-0.4Fe2O3)]·xRySO4, where x = 0-0.5 in increments of 0.1 and R = Li, Na, K, Mg, Ca, Ba, or Pb and y = 1 or 2. In most cases the vast majority or all of the sulfate volatalizes and quarternary P2O5-Fe2O3-FeO-RyOz glasses or partially crystalline materials are formed. Here we have characterized the structure, thermal properties, chemical durability and redox state of these materials. Raman spectroscopy indicates that increasing modifier oxide additions result in depolymerization of the phosphate network such that the average value of i, the number of bridging oxygens per -(PO4)-tetrahedron, and expressed as Q i , decreases. Differences have been observed between the structural effects of different modifier types but these are secondary to the amount of modifier added. Alkali additions have little effect on density; slightly increasing Tg and Td; increasing α and Tliq; and promoting bulk crystallization at temperatures of 600-700 °C.Additions of divalent cations increase density, α, Tg, Td, Tliq and promote bulk crystallization at temperatures of 700-800 °C. Overall the addition of divalent cations has a less deleterious effect on glass stability than alkali additions.57 FeMössbauer spectroscopy confirms that iron is present as Fe 2+ and Fe 3+ ions which primarily occupy distorted octahedral sites. This is consistent with accepted structural models for iron phosphate glasses. The iron redox ratio, Fe 2+/ΣFe, has a value of 0.13-0.29 for the glasses studied. The base glass exhibits a very low aqueous leach rate when measured by Product Consistency Test B, a standard durability test for nuclear waste glasses. The addition of high quantities of alkali oxide (30-40 mol% R2O) to the base glass increases leach rates, but only to levels comparable with those measured for a commercial soda-lime-silica glass and for a surrogate nuclear waste-loaded borosilicate glass. Divalent cation additions decrease aqueous leach rates and large additions (30-50 mol% RO) provide exceptionally low leach rates that are 2-3 orders of magnitude lower than have been measured for the surrogate waste-loaded borosilicate glass. The P2O5-Fe2O3-FeO-BaO glasses reported here show particular promise as they are ultra-durable, thermally stable, lowmelting glasses with a large glass-forming compositional range.

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High-resolution neutron powder diffraction and tr-v-e field ~S R mea. surements have been used to examine the nature of the magnetic and structural transition at 100 K in YMn2. The neutron measurements indicate a first-order hysteretic transition occurring at 92.5 K on cooling and 108 K on warming. The low-temperat-phase is tetragonal (./a = 0.995) and antiferromagnetic with localized Mn moments of 2.8 pg ordering i n a long-wavelength helix characterized by an antiferromaeetic translation vector (T, 7') 1) where T = 0.018 and T' = 0.003. The high-temperat-phase is cubic and Pauli paramagnetic, The collapse of the Mn moment at the transition is accompanied by a 5% decrease in the cell volume. In the paramagnetic state of YMn? measurement of the muon transverse relaxation rate reveals an underlying second-order transition which we assodate with the critical slowing of longitudinal spin fluctuations as the transition temperatureis approached.

The crystal and magnetic structure of the C15 Laves phase of HoMn2 was restudied using powder neutron diffraction. High-resolution spectra showed HoMn2 to remain cubic Fd3m below the magnetic transition temperature. The Ho spins assume a spin-canted ferromagnetic structure with 7.9 mu B per Ho atom. One out of four Mn sites carries a moment of 0.6 mu B induced by the strongly polarizing magnetic environment of ferromagnetically coupled near-neighbour (111) planes of rare-earth spins. A small thermal expansion anomaly accompanied by a spin reorientation is found at the Curie point of 25 K; the Neel point of the system lies at 31 K.

The evolution with temperature of the magnelic structure of the C15 Laves-phase compound DyMn2 has been studied using powder neutron diffraction and magnetization techniques. The Dysublattice assumesa spin-canted ferromagneticstructure with 8.8 pBper Dy atom. Alrhough all Mn sites within the unit cell are chemically equivalent, only one Mn atom in four is found to possess a magnetic moment (of 1.4 ps). These magnetic Mn atoms are located at sites with a strongly polarizing magnetic environment resulting from a nearneighbour configuration of ferromagnetically mupled Dy spins. A spin reorientation is observed at 36 K. and is accompanied by a small thermal expansion anomaly. The Curie temperature of DyMn,is found to be 45 K.