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1

The Effect on Highly Cr-Substituted Manganite Nd_{0.6}C a_{0.4}(Mn_{0.5}Cr_{0.5})O_3

100%

Gamari-Seale H., Troyanchuk I., Bushinsky M., Stefanopoulos K., Hernandez-Velasco J.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

81-86

EN

Neutron powder-diffraction experiments on the highly Cr-substituted manganite, Nd_{0.6}Ca_{0.4}(Mn_{0.5}Cr_{0.5})O_3, at different temperatures and fields reveal that the structure retains the charge exchange-type of the parent compound, Nd_{0.6}Ca_{0.4}MnO_3. It is antiferromagnetic below 200 K and becomes a canted antiferromagnet below 50 K. The Mn and Cr form zig-zag ferromagnetic chains coupled antiferromagnetically in the ac-plane. These are stacked along the b-axis with opposite spins.

2

Orbital Correlations and Magnetic Phase Transitions in Lightly Doped La_{0.88}MnO_x and LaMn_{0.94}O_y Manganites

100%

Troyanchuk I., Khomchenko V., Tovar M., Szymczak H., Bärner K.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

27-44

EN

The results of X-ray and neutron diffraction study as well as the elastic, magnetic, and electrotransport properties of La_{0.88}MnO_x (2.82≤ x≤2.96) and LaMn_{0.94}O_y (2.91≤ y≤3.00)$ manganites have been presented. Under oxygen doping, the transitions from antiferromagnetic to ferromagnetic or spin-glass state are observed for La-deficient and La-excessive series, respectively. These transitions have been found to correlate with the change of the type of Jahn-Teller distortions from static to dynamic ones. The dynamic orbital correlations favor a ferromagnetic state, while an A-type antiferromagnetic state is typical of the static Jahn-Teller distortions. It is argued that the canting magnetic structure in manganites is not realized. The transition to a ferromagnetic or spin-glass state occurs via the formation of inhomogeneous state with different types of orbital correlations and magnetic structure. The key role of intrinsic chemical inhomogeneity in the formation of inhomogeneous magnetic states in solid solutions of manganites is emphasized.

3

Crystal Structure and Chemical Characterization of La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_{x}O₃ (0 ≤ x ≤ 0.15) Compounds

100%

Troyanchuk I., Bushinsky M., Tereshko N., Fedotova V., Partyka J.

Acta Physica Polonica A

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2017

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vol. 132

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issue 2

240-244

EN

Neutron powder diffraction and magnetization measurements have been performed for La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_xO₃ (0 ≤ x ≤ 0.15) stoichiometric compounds. Increase of the Al³⁺ content enlarges the Mn⁴⁺ ions fraction from 0% (x=0) up to around 20% (x=0.15). The x=0 composition around 150 K exhibits a structural transition from the rhombohedral phase to the orthorhombic one whereas the crystal structure of the compounds with x=0.1 and 0.15 remains to be rhombohedral down to 2 K. The substitution of Ti⁴⁺ by Al³⁺ ions is accompanied by a gradual increase in the bond angle Mn-O-Mn and decrease in the Mn-O bond length which lead to enhancement of the covalent component of the chemical bond. All these compounds exhibit ferromagnetic components below 100 K. Magnetic moments estimated per manganese from the neutron powder diffraction data are found to be around 1.3 μ_{B} (x=0) and 1.7 μ_{B} (x=0.1 and 0.15) at 2 K. It is suggested that ferromagnetism is originated predominantly from the Mn³⁺-O-Mn³⁺ and Mn³⁺-O-Mn⁴⁺ superexchange interactions whereas bond angles fluctuation leads to magnetic frustrations. Enhancement of covalence slightly increases ferromagnetism.

4

Thermoelectric Properties of Ca_3Co_4O_9-Based Ceramics Doped with Fe and/or Y

73%

Fedotov A., Fedotov A., Mazanik A., Svito I., Saad A., Troyanchuk I., Bushinski M., Fedotova V., Zukowski P., Koltunowicz T.

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vol. 125

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issue 6

1344-1347

EN

We describe here structure and temperature dependences of conductivity σ(T), the Seebeck coefficient α(T), thermal conductivity λ(T) and figure-of-merit ZT(T) in Ca_3Co_4O_9 ceramics, doped with Fe and Y, depending on compacting pressure (0.2 or 6 MPa) and temperature (300 < T < 700 K). It is shown that introduction of iron and yttrium to ceramics does not alter the crystalline structure of the material. Increasing the pressure in the compacting process before the additional diffusion annealing leads to a smaller-grained structure and increase σ and λ due to reducing of the synthesized samples porosity. The Seebeck coefficients of nanocomposite ceramics Ca_3Co_{3.9}Fe_{0.1}O_9 and (Ca_{2.9}Y_{0.1})(Co_{3.9}Fe_{0.1})O_9 have linear dependences on temperature is not changed after increase of compacting pressure. Electrical-to-heat conductivity ratio (σ/λ) for the samples compacted at high (6 GPa) pressure increases not more than 20-30% in comparison with ones compacted at low (0.2 GPa) pressure, whereby ZT is increased more than 50%. The main reason for this effect is samples porosity reduction with the compacting pressure increase.

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The Effect on Highly Cr-Substituted Manganite Nd_{0.6}C a_{0.4}(Mn_{0.5}Cr_{0.5})O_3

Orbital Correlations and Magnetic Phase Transitions in Lightly Doped La_{0.88}MnO_x and LaMn_{0.94}O_y Manganites

Crystal Structure and Chemical Characterization of La_{0.7}Sr_{0.3}Mn_{0.7}Ti_{0.3-x}Al_{x}O₃ (0 ≤ x ≤ 0.15) Compounds

Thermoelectric Properties of Ca_3Co_4O_9-Based Ceramics Doped with Fe and/or Y