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Possible ferromagnetic and ferroelectric orders in ceramicBi1–xLaxMnO3(x= 0.0, 0.1, and 0.2) samplesprepared under 3–6 GPa pressure have been investigated. Rietveldfits to powder neutron diffraction data show that BiMnO3and Bi0.9La0.1MnO3adopt a monoclinic C2/cperovskite superstructure whereasBi0.8La0.2MnO3has orthorhombic Pnmasymmetry. Both structural analysis and Curie–Weissfits to magnetic susceptibility data show that high spin d4Mn3 present with no significant Bi deficiencyor Mn4犉 apparent. La substitution suppresses themagnetic Curie temperature of the monoclinic phase from 105 K for x= 0 to 94 K at x= 0.1, but the x= 0.2 material shows antiferromagnetic order similar tothat of LaMnO3. Impedance spectroscopy and dielectric measurementson the x= 0.1 and 0.2 materials show modest bulkpermittivity values (45–80) down to 50 K, and there is no strongevidence for ferroelectric behavior. The two samples have thermallyactivated conductivities with activation energies of 0.21–0.24eV. [ABSTRACT FROM AUTHOR]

An investigation of Ca substitution in the multiferroic material BiFeO3shows that a wide range of perovskites BixCa1−xFeO3(0.4 ≤ x≤ 1.0) can be prepared by sintering in air at 810−960 °C. 0.4 ≤ x< 0.8 samples are cubic Pm3̅m, whereas x= 0.8 and 0.9 show a coexistence of the cubic and the rhombohedral R3cBiFeO3-type structure. Considerable disorder arising from Bi3+lone-pair distortions is evidenced by synchrotron X-ray and neutron studies of the average structures of the cubic phases, and electron microscopy reveals commensurate and incommensurate local superstructures. The BixCa1−xFeO3(0.4 ≤ x≤ 1.0) materials show a remarkably robust antiferromagnetic order with TN= 623−643 K and ordered moments of 3.6−4.1 μB. They are “leaky” dielectrics with relative permittivities of ∼30−100 and bulk resistivities ∼50−500 kΩ cm at room temperature. The activation energy for bulk conduction increases from 0.27 eV for x= 0.4 to 0.5 eV for x= 1, but with a discontinuity at the cubic-rhombohedral boundary. Further processing of the x= 0.8 and 0.9 compositions to reduce conductivity through control of oxygen content could lead to improved BiFeO3-based multiferroics. [ABSTRACT FROM AUTHOR]

The relationships between the intervalence energy (E[subIT]) and the free energy difference (AG) that exists between the minima of redox isomers (Fe[supII]-Ru[supIII]/Fe[supIII]-Ru[supIII]) for various heterobimetallic complexes [(R-Fcpy)Ru(NH[sub3])[sub5]][sup2+/3+] (R = H, ethyl, Br, actyl; Fcpy = (4-pyridyl)ferrocenyl; Ru(NH[sub3])[sub5] = pentaam(m)ineruthenium) were examined. The changes in ΔG for the complexes in various solvents were due to the effects of both solvent donicity and the substituents. The intervalence energy versus ΔG, ΔG ≈ FAE112 (AE112 = E112(Fe°') - E112(Ru'°")), plots for the complexes in various solvents suggest a nuclear reorganization energy ()L) of 6OOO cm1 (Chen et al. !norg. Chem. 2000, 39, 189). For [(R-Fcpy)Ru(NH3)5]2 and [(et-Fcpy)Ru(NH3)4(py)]2 (Ru(NH3)4 = trans-tetraam(m)ineru- thenium; py = pyridine) in various solvents, the E112(Ru'°'°) of rutheniumam(m)ine typically was less than the E1/2(F°'°) of the ferrocenyl moiety. However, the low-donicity solvents resulted in relatively large values of E112(Ru"°) for [(et-Fcpy)Ru(NH3)4(py)]234t Under our unique solvent conditions, a dramatic end-to-end interaction was observed for the trimetal cation, [(et-Fcpy)2Ru(NH3)4]4, in which the [(et-Fcpy)2Ru(NH3)4]4 included a central trans-tetraam(m)ineruthenium(lll) and a terminal Fe°/Fe'° pair. In general, results of electrochemical studies of [(et- Fcpy)2Ru(NH3)4]2 indicated both solvent-tunable E112(Ruu1/11) (1 e) and solvent-insensitive E112(Fe°"°) (2 e-) redox centers. However, in nitriles, two Eii2(Fevu) peaks were found with E112(Fe" - Fe°) ranging between 83 and 108 mV at a terminal metal-to-metal distance of up to 15.6 A. Furthermore, the bridging dr orbital of the ruthenium center mediated efficient end-to-end interaction between the combinations of the terminal Fe°-Fe°'/Fe°'-F&' pair. To our knowledge, this is the first example of solvent-tunable end-to-end interactions in multimetal complexes. [ABSTRACT FROM AUTHOR]

Solid solutions of Pauli-paramagnetic CaCu3V4O12 and antiferromagnetic CaMn3V4O12 were prepared by a high-pressure synthesis technique. All samples crystallized in the A-site-ordered perovskite structure with isovalent Cu2+ and Mn2+ ions at the square-planar A' site. The V ion at the B site kept a charge state close to +4 in all of the solid solutions, and the electrons of V were delocalized and contributed to the metallic properties. The substitution of Mn2+ for Cu2+ in CaCu3V4O12, where both Cu and V electrons were delocalized, produced the S = 5/2 localized moments, and the spins at the Mn site interacted antiferromagnetically. Spin-glass-like magnetic behaviors due to the random distribution of Cu/Mn ions at the A' site were observed at intermediate compositions of the solid solution, whereas the antiferromagnetic transition was observed at the end composition CaMn3V4O12. [ABSTRACT FROM AUTHOR]

Ultra-high-resolution neutron diffraction studies of BiFe0.8Co0.2O3 show a transition from a cycloidal space modulated spin structure at T = 10 K to a collinear G-type antiferromagnetic structure at T = 120 K. The model of antiparallel directions of Fe3+ and Co3+ magnetic moments at the shared Wyckoff position describes well the observed neutron diffraction intensities. On heating above RT, the crystal structure of BiFe0.8Co0.2O3 changes from a rhombohedral R3c to a monoclinic Cm. At 573 K only the Cm phase is present. The collinear C-type antiferromagnetic structure is present in the Cm phase of BiFe0.8Co0.2O3 at RT after annealing. [ABSTRACT FROM AUTHOR]

A-site-ordered perovskite-structure oxides with Mn and V at A' and B sites, respectively, were synthesized by using a high-pressure method. Valence-state analyses revealed that the A-site substitution modulated the valence states of the Mn ions at the A' site and V ions at the B site sequentially. By changing the A-site ions from Na+ to Ca2+ and from Ca2+ to La3+, the valence distribution changed site-selectively from Na+Mn2.33+ V4+4O12 to Ca2+Mn2+3V4+4O12 and to La3+Mn2+3V3.75+4O12. The electrons of the A'-site Mn were localized and contributed to the magnetic properties, that is, spin-glass-like behavior in NaMn3V4O12 and antiferromagnetic behavior in CaMn3V4O12 and LaMn3V4O12. The valence electrons of the B-site V, in contrast, were delocalized, as could be seen from the low resistivity of the samples. The delocalized electrons at the B-site V did not correlate with the localized spins at the A'-site Mn. [ABSTRACT FROM AUTHOR]

dc and ac magnetic susceptibility, magnetization, specific heat, and Raman scattering measurements are combined to probe low-lying spin excitations in α-Ru1-xIrxCl3 (x≈0.2), which realizes a disordered spin liquid. At intermediate energies (ℏω>3  meV), Raman spectroscopy evidences linearly ω-dependent Majorana-like excitations, obeying Fermi statistics. This points to robustness of a Kitaev paramagnetic state under spin vacancies. At low energies below 3 meV, we observe power-law dependences and quantum-critical-like scalings of the thermodynamic quantities, implying the presence of a weakly divergent low-energy density of states. This scaling phenomenology is interpreted in terms of the random hoppings of Majorana fermions. Our results demonstrate an emergent hierarchy of spin excitations in a diluted Kitaev honeycomb system subject to spin vacancies and bond randomness. [ABSTRACT FROM AUTHOR]

We report on magnetization M(H), dc and ac magnetic susceptibility χ(T), specific heat Cm(T) and muon spin relaxation (μSR) measurements of the Kitaev honeycomb iridate Cu2IrO3 with quenched disorder. In spite of the chemical disorders, we find no indication of spin glass down to 260 mK from the Cm(T) and μSR data. Furthermore, a persistent spin dynamics observed by the zero-field muon spin relaxation evidences an absence of static magnetism. The remarkable observation is a scaling relation of χ[H,T] and M[H,T] in H/T with the scaling exponent α=0.26-0.28, expected from bond randomness. However, Cm[H,T]/T disobeys the predicted universal scaling law, pointing towards the presence of additional low-lying excitations on the background of bond-disordered spin liquid. Our results signify a many-faceted impact of quenched disorder in a Kitaev spin system due to its peculiar bond character. [ABSTRACT FROM AUTHOR]