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Dielectric measurements are used for characterizing the magnetic phase transitions in the doped ferroelectric oxides [Ho.sub.1-x][Y.sub.x]Mn[O.sub.3] (x = 0-0.8) and the effects of the magnetic field direction and Y doping on the reentrant T-B-[THETA] phase diagrams below Neel temperature are examined. The magnetic field anisotropic study is very important for understanding the magnetic and electric phase competition in the diluted Ho 4 f hexagonal system by the nonmagnetic ion yttrium.

A study was conducted to measure magnet susceptibility, electrical resistivity, specific heat, and Seebeck coefficient of Hastelloy C-276 from 2 to 300 K and thermal conductivity from 2 to 200 K. The data from the measurement can be used for the specific applications of the superconducting coated conductors that use Hastelloy C-276 as substrates for many cryogenic temperature applications.

Abstract: A newly discovered 1:3 A-site-ordered AA′3B4O12 perovskite oxide CaCu3Ir4O12 which has unusual electrical and magnetic properties was investigated using STEM imaging and EELS techniques in a probe corrected microscope. The target sample was compared with the other two iso-structural oxides of CaCu3Ru4O12 and CaCu3Ti4O12 with dissimilar physical properties. It has been found by STEM HAADF imaging that Ca and Cu on A and A′ sites are ordered as expected. Oxygen atoms are imaged with STEM ABF imaging. The fine structures of the Cu L2,3 core loss and O–K edges show that the electronic structure of CaCu3Ir4O12 is very close to that of CaCu3Ru4O12, but different from CaCu3Ti4O12. The O–K near edge fine structures show extensive hybridization of Ir 5d and O 2p band. Cu L2,3 peaks indicate Cu in CaCu3Ir4O12 has 2+ valence, though Cu2+ electrons mainly localized, they might have strong interactions with Ir4+ 5d electrons through IrOCu, similar to the strong coupling of Ru with Cu in CaCu3Ru4O12. [Copyright &y& Elsevier]

Abstract: Single crystals of the spin dimer compound Pb2V3O9 were grown for the first time by the floating zone method. Room temperature single-crystal X-ray diffraction measurements confirm their crystallinity and structure. The crystal growth process is discussed in detail and high temperature differential scanning calorimetry measurements that show a structural phase transition from a monoclinic to a triclinic unit cell at 759(1)K are presented. [Copyright &y& Elsevier]

Abstract: The pyrochlores in the series A 2Sb2O7 have been synthesized and characterized as exhibiting spin glass transitions at T SG=41, 4.5, and 2.6K (for A=Mn2+ , Co2+ and Ni2+ S=1, respectively) despite the lack of chemical disorder. Since the Curie–Weiss temperature remains essentially constant for all members in the series (), the frustration index for these materials increases significantly as the moment size is reduced from (Mn2+), to 9.3 (Co2+) to 14.6 (Ni2+). There is also a corresponding change in the spin dynamics measured by the shift in the AC susceptibility signal as a function of frequency. These new materials provide an avenue to investigate the effect of quantum fluctuations on the Heisenberg pyrochlore lattice in the low spin limit, and show there is a dramatic change in the spin dynamics as the quantum regime is approached. [Copyright &y& Elsevier]

Abstract: For comparison with the Mn4+/Mn3+ oxoperovskites at the crossover from localized to itinerant behavior of the σ-bonding e electrons, the electronic properties of three oxygen non-stoichiometric, mixed-valent Fe4+/Fe3+ oxoperovskites were explored by measuring their resistivity ρ(T), thermoelectric power α(T), and magnetic susceptibility χ(T). Oxidation of Ca2Fe2O5 by annealing in ozone progresses by oxygen insertion to give conductive CaFeO3 perovskite clusters in a localized-electron, weakly oxidized brownmillerite Ca2Fe2O5+ δ matrix. Removal of 0.12 oxygen per formula unit from La1/3Sr2/3FeO3 lowers somewhat its cooperative disproportionation reaction, and fivefold-coordinated ions neighboring oxygen vacancies in the more ionically bonded slabs act as donors to the covalently bonded Fe(V)O6 planes. Single-crystal SrFeO2.83 exhibited bad-metal behavior with superparamagnetic, electron-rich fluctuations below 240K that, on cooling below 190K, become progressively trapped by the oxide-ion vacancies as an immobile second phase; long-range antiferromagnetic order is stabilized below a T N≈60K. [Copyright &y& Elsevier]

The temperature dependence of the paramagnetic susceptibility χm(T) taken in 2500 Oe, the resistivity ρ(T), and the thermoelectric power α(T) of DyBaCo2O5+x, which has Ba and Dy ordered into alternate (001) planes of an oxygen-deficient perovskite, have revealed a phase segregation in the compositional range 0.3x<0.5. Orthorhombic DyBaCo2O5.51 has, in addition, oxygen vacancies ordered into alternate rows of the DyO0.51 (001) planes; a cold-pressed polycrystalline sample exhibits a first-order insulator–metal transition at TIM=320 K, a Curie temperature TC=300 K, and a broadened metamagnetic transition temperature TM≉265 K in 2500 Oe. A ferromagnetic M–H hysteresis curve fails to saturate at 5 T, and a minority ferromagnetic phase below TM has a volume fraction that decreases with decreasing temperature, vanishing below 50 K. Oxygen vacancies in the DyBaCo2O5.5 phase suppress the metallic state; interstitial oxygen does not. A thermoelectric power α(T)>0 of DyBaCo2O5.51 changing continuously across TIM is interpreted to manifest a metallic minority phase crossing a percolation threshold; α(T) also provides evidence for a progressive excitation of higher-spin Co(III) with increasing temperature from below 50 K to above TIM. A previous model of the RBaCo2O5.5 phase is extended to account for the Ising spin configuration below TC, the magnetic order in the presence of higher-spin octahedral-site Co(III), and the α(T) data. [Copyright &y& Elsevier]

The morphologies of the charge carriers in the perovskite system SrFe1-xTixO3-δ are explored by transport and magnetic measurements. Oxygen vacancies are present in all samples, but they do not trap out the Fe3+ ions they introduce. The x=0.05 composition was prepared with three different values of δ. They all show small-polaron conduction above 225 K; but where there is a ratio c=Fe4+/Fe<0.5, the polaron morphology appears to change progressively with decreasing temperature below 225 K to two-Fe polarons that become ferromagnetically coupled in an applied magnetic field at lower temperatures; With an applied field of 2500 Oe, divergence of the paramagnetic susceptibility for zero-field-cooled and field-cooled samples manifests a greater stabilization of ferromagnetic pairs on cooling in the applied field. With a c>0.5, the data are consistent with a disproportionation reaction 2Fe4+=Fe3++Fe(V)O6/2 that inhibits formation of two-Fe polarons and, on lowering the temperature, creates Fe3+–Fe(V)–Fe3+ superparamagnetic clusters. [Copyright &y& Elsevier]

The longitudinal and transverse ultrasonic velocities and attenuations, the transport and magnetic properties, as well as the structural changes of polycrystalline La[sub 0.25]Ca[sub 0.75]Mn[sub 0.93]Cr[sub 0.07]O[sub 3] have been studied systematically. A velocity minimum and an attenuation peak for both longitudinal and transverse waves occur around the temperature T[sub co] of charge ordering transition accompanied by the structural change from a cubic to a tetragonal phase. Near temperature T[sub N] (where the c-axis length shows a maximum), the sharp decrease of velocities for both waves and the appearance of a longitudinal attenuation peak are attributed to the antiferromagnetic transition together with the anomalous change in c-axis length of the tetragonal phase. The simultaneous occurrence of the ultrasonic, lattice, charge ordering, magnetic, and transport anomalous characteristics indicates the strong electron-phonon and spin-phonon interactions in the system. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The in-plane resistivity of Bi2Sr2CaCu2O8+δ single crystal in different magnetic fields was measured for magnetic field H parallel and perpendicular to the CuO2 plane. The irreversibility line Hirr⊥c(T) for H parallel to the CuO2 plane locates in higher field and higher temperature region in the H–T phase diagram than Hirr&par;c(T) for H perpendicular to the CuO2 plane. Hirr&par;c(T) is dominated by surface barrier pinning, while Hirr⊥c(T) shows different temperature dependencies above and below 2 T, which may indicate different energy dissipation above and below the field. The field dependence of activation energy above 2 T in H⊥c configuration could be explained by vortex–antivortex expansion in CuO2 plane. [Copyright &y& Elsevier]

Abstract: Spin liquids, multiferroics, and doubly-chiral helical structures are just some of the exotic magnetic states found in the langasite compounds. A subclass of the langasite group, the Te6+-containing dugganites, has also shown exotic magnetism including magnetoelectric coupling, coexisting complex long-ranged ordered structures, and low-field induced magnetic transitions. Here, we present the first detailed structural study of Pb3TeMn3P2O14 as well as the first neutron scattering measurements. This material undergoes long-range magnetic ordering, similar to the multiferroic Ba3NbFe3Si2O14, at T N =6.6K, which is consistent with previous magnetization measurements. However unlike any other langasite or dugganite studied to date, we present evidence of a large, pseudohexagonal incommensurate supercell that alters the nuclear and magnetic structures away from the langasite ideal. [Copyright &y& Elsevier]