Neutron powder diffraction study of TbBaCo2−xFexO5+γ layered oxides

The crystal and magnetic structures of layered perovskites TbBaCo_2−xFe_xO_5+γ (0.08?x?0.24) were studied by neutron powder diffraction. Increasing iron concentration up to the x values higher than 0.10 leads to the orthorhombic→tetragonal phase transition resulting from the transformation of 2×1×1-type superstructure, formed due to ordering of extra oxygen incorporated into the vacant sites in [TbO_γ] layers, into 3×3×1 superlattice. The concentration ranges, where the orthorhombic and tetragonal lattices exist, are separated with a narrow two-phase domain. For the tetragonal phases with 3×3×1 superstructure (space group P4/mmm), the Co/Fe ions are antiferromagnetically coupled, forming G-type spin-ordered configuration. The Co³⁺ cations located in square-pyramidal sites adopt intermediate spin state, whilst a relatively small magnetic moment of Co³⁺ ions in the octahedral sublattice indicates that a minor fraction of cobalt is in the low-spin state.     

The two-phase crystal structure and magnetic properties of the LaCo<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>x</Subscript>O<Subscript>3−<Emphasis Type="Italic">d</Emphasis></Subscript> system

The preparation conditions and magnetic properties of the La(Co_1?xFe_x)O3?d system of solid solutions were studied. Irrespective of synthesis conditions, the samples with x ≤ 0.15 were rhombohedral (space group \(R\bar 3c\)), and those with x ≥ 0.7, orthorhombic (space group Pnma). In the intermediate region of 0.15 < x < 0.7, the samples could be mixtures of rhombohedral and orthorhombic phases. Structural heterogeneity considerably decreased as the temperature of the synthesis increased or after annealing in a reducing medium. The samples containing more than 40% iron exhibited weak spontaneous magnetization, as is characteristic of weak ferromagnets. The magnetic properties and structure depend on the content of oxygen. A decrease in the concentration of oxygen sharply increases magnetic anisotropy; the coercive force is then close to 10 kOe, which is more than that known for other oxide systems. The magnetic properties are explained in terms of the model according to which Co³⁺ ions are in the low-spin state.     

Spin state of cobalt ions in NdCoO3

The crystal structure of NdCoO₃ is studied by neutron diffraction. It is shown that static cooperative Jahn—Teller distortions are absent up to the temperature of transition to the metallic state. The results are discussed within the model considering the transition of cobalt ions from the low-spin to the intermediate-spin state by gradual thermal excitation without a clearly pronounced critical behavior.     

Magnetic Study of OrthomanganitesA1−xMnO3+y(A=La, Eu) with the Perovskite Structure

The crystal structure and magnetic properties of orthomanganitesA_1−xMnO_3+y(A=La, Eu;x≤0.2;y≤0.13) were investigated. It was shown that the increase of oxygen content leads to the transformation from the weak ferromagnetic to the ferromagnetic state in these compounds. The Curie temperatures of La_1−xMnO_3+yand freezing temperatures of magnetic clusters for Eu_1−xMnO_3+yin the samples with a deficit ofAcations are higher than those in parent compounds (withx=0). A mixed magnetic state involving ferro- and antiferromagnetic domains is suggested in the intermediate range ofx,yvalues. Arguments are presented to support the assumption that the magnetic properties in the lightly doped insulating regime are governed by superexchange via anions rather than by exchange via charge carriers.     

Structural,ferroelectric and magnetic properties of Bi0.85Sm0.15FeO3 perovskite

Room temperature crystal structure, ferroelectric and magnetic properties of polycrystalline Bi_0.85Sm_0.15FeO₃ samples were investigated. X‐ray diffraction study shows that the compound possesses a dominant PbZrO₃‐like orthorhombic structure with √2a ×2√2a ×2a superlattice (a is the parameter of the cubic perovskite subcell). In contrast to piezoresponse force microscopy data demonstrating some features characteristic of ferroelectrics, polarization vs. electric field measurements reveal the behavior expected for nonpolar materials. Investigation of magnetic properties confirms that 15% samarium substitution suppresses the spin modulation typical of BiFeO₃ and induces the appearance of spontaneous magnetization. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electric and magnetic properties of the perovskites Ba2(FeMo)O x (5.88 ≤ x 6.01)

The purpose of this work is to establish the relation between the magnetic, electric, and magnetotransport properties and the oxygen nonstoichiometry of the compounds Ba₂(FeMo)O _x (5.88 ≤ x ≤ 6.01). The investigations established the behavior of the magnetization, resistance, and magnetoresistance of samples in this series. It is shown that the behavior of the magnetization can be described by assuming that the iron ions become divalent (Fe³⁺→ Fe²⁺) as a result of the reduction of the samples and the molybdenum ions become hexavalent (Mo⁵⁺ → Mo₆₊) as a result the oxidation of the samples. It is established that there are two contributions to the magnetoresistance which arise as result of magnetic ordering of the intragranular interlayer and intergranular transfer of spin-polarized charge carriers. It is inferred that electric transport in samples of this series is determined by percolation processes between granules with metallic conductivity separated by a dielectric interlayers.     

Enhanced ferroelectric, magnetic and magnetoelectric properties of Bi1−xCaxFe1−xTixO3 solid solutions

We report on the enhanced electromechanical, magnetic and magnetoelectric properties of Bi_1−xCa_xFe_1−xTi_xO₃ solid solutions. The crystal structure of the x≈0.25 compounds are close to the rhombohedral-orthorhombic phase boundary, and the solid solutions are characterized by increased electromechanical properties due to the polarization extension near the polar-nonpolar border. The homogenous weakly ferromagnetic state is established at x>0.15 doping. The chemical doping shifts the magnetic transition close to room temperature, thus enlarging the magnetic susceptibility of the compounds. The solid solutions at the morphotropic phase boundary exhibit a nearly twofold increase in piezoelectric response, whereas the magnetoelectric coupling shows five times enhancement in comparison with the parent bismuth ferrite.     

Spin Crossover and Magnetic Properties of Ba-Substituted Cobaltites

Journal of Experimental and Theoretical Physics - The dependence of the properties of the La0.45Ba0.55CoO3 – δ and La0.4Ba0.6CoO3 – δ cobaltites on the oxygen content has been...