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...     

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.     

Crystal structure and properties of Bi1 ? x Ca x FeO3 and Bi1 ? x Ca x FeO1 ? x Ti x O3 solid solutions

Systems of solid solutions Bi_{1 − x} Ca _x FeO₃ (I) and Bi_{1 − x} CaxFeO_{1 − x} Ti _x O₃ (II) have been obtained and their properties have been studied using neutronography and M?ssbauer spectroscopy; magnetization and permittivity have been measured. It is shown that an increase in the concentration of calcium ions in system I for x > 0.2 changes rhombohedral distortions of a unit cell (space group R3c) to tetragonal distortions (space group I4/mcm), while rhombohedral distortions in system II for x > 0.2 are replaced by orthorhombic distortions (space group Pnma). Analysis of the crystal structure has revealed strong anisotropy in vibrations of Bi and O ions in system I compounds. Systems I and II are characterized by G-type antiferromagnetic ordering of magnetic moments. In system II, spontaneous magnetization associated with the Dzyaloshinskii-Moriya interaction has been detected. According to M?ssbauer spectroscopy data, iron ions in compounds I and II are in the trivalent state and charge compensation occurs due to the formation of oxygen vacancies. The permittivity increases with the calcium concentration. Original Russian Text ? I.O. Troyanchuk, D.V. Karpinsky, M.V. Bushinskii, O. Prokhnenko, M. Kopcevicz, R. Szymczak, J. Pietosa, 2008, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2008, Vol. 134, No. 1, pp. 105–112.     

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.     

Structural investigation of anion-deficient manganites La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3 − δ</Subscript>

The crystal structure of the anion-deficient manganites La_0.7Sr_0.3MnO_{3 ? δ} (δ = 0, 0.10, 0.15, 0.20) is investigated using high-resolution neutron diffraction. At room temperature, the crystal structure of the stoichiometric manganite La_0.7Sr_0.3MnO₃ and the anion-deficient manganite La_0.7Sr_0.3MnO_2.9 is satisfactorily described in rhombohedral space group R \(\bar 3\) c. The anion-deficient manganite La_0.7Sr_0.3MnO_2.85 is characterized by two perovskite phases with space groups R \(\bar 3\) c and 14/mcm. The crystal structure of the La_0.7Sr_0.3MnO_2.8 manganite corresponds to the structure of a perovskite phase with space group I4/mcm. It is established that the phase separation in the crystal structure of the La_0.7Sr_0.3MnO_{3 ? δ} manganites at a temperature of 293 K is associated with a nonuniform distribution of oxygen vacancies.     

First-order magnetic phase transition in layered Sr3YCo4O10.5 + δ-type cobaltites

JETP Letters - In layered Sr3YCo4O10.5 + δ-type cobaltites with different oxygen contents, we have observed a first order magnetic phase transition from the high-temperature...     

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.