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A triangular-lattice antiferromagnet of Ag_{2}FeO_{2} was synthesized under high pressure. Its magnetism was studied in terms of electrical resistivity, magnetic susceptibility, heat capacity, powder neutron scattering, and Mössbauer spectroscopy. The magnetic state of Ag_{2}FeO_{2} changes successively through a second-order phase transition at T_{p}=36 K and a crossover at T_{c}=20 K. A partially disordered (PD) state appears below T_{p}, in which ≈2/3 spins are ordered and the remaining ≈1/3 spins fluctuate, which state persists at least down to 5 K. The spin correlation length starts to grow at T_{p}; however, it remains very short (≈27 Å) below T_{c}. This exotic magnetism is concerned with strong frustration in the classic antiferromagnetic triangular lattice.

Abstract We have carried out 99/101Ru-NMR, measurements at zero magnetic field in magnetic superconductors RuEu1.4Ce0.6Sr2Cu2O10-d and RuSr2YCu2O8 to investigate charge and magnetic states of Ru ions in its magnetically ordered state. In RuEu1.4Ce0.6Sr2Cu2O10-d, only one Ru site corresponding to Ru5+ ions with S=3/2 high spin state was shown to exist. This contrasts sharply to the case of RuSr2YCu2O8 where two kinds of Ru sites of Ru5+ (S=3/2) and Ru4+ (S=1) were observed. These results indicate the magnetic and charge states of the Ru ions in the RuO2 planes are different for both systems. [ABSTRACT FROM AUTHOR]

Heavily potassium-substituted barium iridates Ba2−xKxIrO4 (x≤0.5) and lanthanum-substituted Ba2−yLayIrO4 (y≤0.05) were prepared for the study of the carrier doping effects on the transport properties of the spin-orbit Mott state. The carrier type is holelike for the nondoped (x = y = 0) and K-doped (x>0) phases, while it is electronlike for the La-doped (y>0) phases. It was found that electron doping is more effective in decreasing the electrical resistivity. This suggests an asymmetry of the density of states between the upper and lower energies of the Fermi level. A semimetallic state emerges for the K-doped phases with x≥0.3 at ambient pressure. More conducting metallic states (ρ∼10−2 Ω cm, dρ/dT>0) were achieved under high pressure for both the K- and La-doped phases. Notwithstanding, no superconductivity was observed in the metallic states down to 4.2 K. The experimental results are discussed with respect to the electronic phase diagram calculated by Watanabe et al. [ Phys. Rev. Lett. 110 027002 (2013)]. [ABSTRACT FROM AUTHOR]