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1

Magnetite Fe_3O_4: the Correlated Electron-Phonon System

100%

Kozłowski A., Kąkol Z., Tarnawski Z.

Acta Physica Polonica A

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2007

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vol. 111

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issue 4

537-547

EN

In the paper the influence of magnetic as well as electron-lattice interactions on the Verwey transition in magnetite related compounds is discussed based on the authors' experimental activity and available literature. While magnetism was proved to only reflect the transition, the results of nuclear inelastic scattering show that lattice dynamics actively participates in it. The studies of diffuse neutron scattering and heat capacity suggest also that the low temperature lattice properties of slightly doped magnetite are distinct from those with higher dopant concentration. Finally, recent theoretical results strongly suggest that the Verwey transition in magnetite cannot be understood and described without strong involvement of electron-lattice interactions.

2

Specific Heat of RBa_{2}Cu_{3}O_{7-x} and RBaSrCu_{3}O_{7-x} Compounds (R = Sm, Dy, Er)

88%

Tarnawski Z., Kim-Ngan N., Wang X., Duijn V., Franse J.

Acta Physica Polonica A

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1998

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vol. 93

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issue 3

513-522

EN

The low-temperature specific-heat C(T) data of high-T_{c} superconductors RBa_{2}Cu_{3}O_{7-x}(R123O_{7-x}) were reviewed. A discussion of the C(T) data obtained on single-crystalline samples of Er123O_{7-x} and Sm123O_{7-x} compounds in applied magnetic fields for better evaluation of the crystal-electric-field parameters is given. The C(T) measurements of Sr-substituted compounds RBaSrCu_{3}O_{7} revealed the λ-type of peak related to the antiferromagnetic order at 1.2 K and 0.6 K respectively for Dy- and Er-compounds. The magnetic singlet ground state in these compounds is produced by weak exchange interactions of -0.05 T/μ_{B} and -0.035 T/μ_{B}, respectively. For Nd- and Sm-compounds, only a broad anomaly around 0.6 K was observed which is well fitted with a Schottky-type anomaly with an energy splitting of 1.4 K.

3

Electronic Properties of High-Temperature Superconductor DyBa_{2}Cu_{3}O_{7} from Critical Fields and Specific Heat Studies

76%

Kołodziejczyk A., Kozłowski A., Chmist J., Zalecki R., Ściężor T., Tarnawski Z., Woch W.

Acta Physica Polonica A

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1993

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vol. 84

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issue 1

127-138

EN

The lower and upper critical fields, as well as the specific heat were measured as a function of temperature for good quality DyBa_{2}Cu_{3}O_{7} high-temperature superconductor in the vicinity of superconducting transition temperature T_{c} = 91.2 K. The number of superconducting and normal state electronic quantities were determined basing on the Ginzburg-Landau-Abrikosov-Gorkov theory. It is argued that on the basis of this BCS-like theory one can describe the superconducting properties and, in combination with some information on the electronic structure, also the magnetic properties of high-temperature superconductors.

4

Studies of the Magnetic Axis Switching in Magnetite

76%

Król G., Kusz J., Tarnawski Z., Kąkol Z., Tabiś W., Kozłowski A.

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EN

The influence of the external magnetic field on magnetic and crystallographic structure of magnetite was studied. We have confirmed, by means of vibrating sample magnetometer measurements, that external magnetic field can switch the easy magnetic axis to the new crystallographic direction. We have also proved by the direct observation of the crystalline structure that this phenomenon is strictly related to the crystallographic structure relaxation.

5

Studies of the Verwey Transition in Magnetite

64%

Tarnawski Z., Wiecheć A., Madej M., Nowak D., Owoc D., Król G., Kąkol Z., Kolwicz-Chodak L., KozŁowski A., Dawid T.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

771-775

EN

Studies of the specific heat and simultaneous AC magnetic susceptibility (ρ') and electric resistance of stoichiometric magnetite single crystal are presented. The temperature hysteresis of the Verwey transition is of 0.03 K found from the specific heat data confirming its first-order character. The continuous temporal change of ρ' at T_V can be switched off by an external magnetic field without affecting the transition. The electrical resistance decreases continuously with increasing temperature with a rapid change of slope at the point when the phase transition is completed. It was concluded that the magnetic degrees of freedom do not actively participate in the transition and that the entropy released at T_V may come from ordering electrons.

6

Study of Ti, V and Their Oxides-Based Thin Films in the Search for Hydrogen Storage Materials

64%

Tarnawski Z., Zakrzewska K., Kim-Ngan N.-T., Krupska M., Sowa S., Drogowska K., Havela L., Balogh A.

Acta Physica Polonica A

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2015

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vol. 128

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issue 3

431-439

EN

Thin film series consisting of Ti, V, TiO₂ and V₂O₅ layer with different layer geometries, sequences and thicknesses have been prepared by the sputtering technique. The hydrogen depth profile of selected films upon hydrogen charging at 1 bar and/or hydrogenation at pressure up to 102 bar was determined by using secondary ion mass spectrometry and nuclear reaction analysis using a N-15 beam. The highest hydrogen storage with a concentration up to 50 at.% was found in the pure Ti and Ti-contained layer, while it amounts to around 30% in the metallic Ti-V-Ni layer. Hydrogen can diffuse through the TiO₂ layer without accumulation, but can be stored in the VO₂ layer in some cases. Hydrogen can remove the preferential Ti orientation in the films and induce a complete transition of V₂O₅ into VO₂ in the films.

7

Structural, Thermal, Magnetic, and Transport Properties of (La_{2/3}Ca_{1/3})(Mn_{1-x}Sn_x)O_{3-δ} Compounds

64%

Przewoźnik J., Chmist J., Kolwicz-Chodak L., Tarnawski Z., Kołodziejczyk A., Krop K., Kellner K., Gritzner G.

Acta Physica Polonica A

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2004

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vol. 106

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issue 5

665-680

EN

The structural, magnetic, and electrical transport properties of Sn-doped manganite La_{0.67}Ca_{0.33}Mn_{1-x} Sn_xO_{3-δ} (x=0, 0.01, 0.03, andδ≈0.06) compounds were studied using X-ray powder diffraction, scanning electron microscopy, AC susceptometer and vibrating sample magnetometer measurements as well as four-probe resistance measurements. The specific heat was measured by the heat-pulse method. The Curie temperature T_C and the metal-insulator transition temperature T_{M-I} decreased nonlinearly with increasing Sn content. The T_C and T_{M-I} values, for the x=0, 0.01, and 0.03 compounds were separated by 18.2 K, 66.3 K, and 10 K, respectively. The resistivity above T_C for all of these compounds followed the Mott variable-range-hopping model. This allowed the estimation of the localization lengths of 2.2Å (x = 0), 1.33Å (x=0.01) and 1.26Å (x=0.03). The x=0 and x=0.01 compounds exhibited anomalies of R(T) at corresponding T_C and allowed the separation of the magnitude of the purely magnetic contribution to the resistance which for x=0 was≈5 .7Ω and for x=0.01,≈22 .4Ω. The specific heat of the Sn-free sample exhibited a sharp peak at T_C. With increasing Sn content the peak at T_C broadened and the area under the peak decreased. For x= 0.03 the peak was hardly detectable. Our results on La_{0.67}Ca_{0.33} Mn_{1-x}Sn_xO_3 reveal that a small substitution of Sn^{4+} for Mn^{4+} suppresses double exchange interactions and strongly affects the magnetic, thermal, and transport properties of the parent compound.

Refine search results

Magnetite Fe_3O_4: the Correlated Electron-Phonon System

Specific Heat of RBa_{2}Cu_{3}O_{7-x} and RBaSrCu_{3}O_{7-x} Compounds (R = Sm, Dy, Er)

Electronic Properties of High-Temperature Superconductor DyBa_{2}Cu_{3}O_{7} from Critical Fields and Specific Heat Studies

Studies of the Magnetic Axis Switching in Magnetite

Studies of the Verwey Transition in Magnetite

Study of Ti, V and Their Oxides-Based Thin Films in the Search for Hydrogen Storage Materials

Structural, Thermal, Magnetic, and Transport Properties of (La_{2/3}Ca_{1/3})(Mn_{1-x}Sn_x)O_{3-δ} Compounds