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1

Doping Effects of Co, Ni, and Cu in FeTe_{0.65}Se_{0.35} Single Crystals

100%

Bezusyy V., Gawryluk D., Berkowski M., Cieplak M.

Acta Physica Polonica A

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2012

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vol. 121

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issue 4

816-819

EN

The resistivity, magnetoresistance, and magnetic susceptibility are measured in single crystals of FeTe_{0.65}Se_{0.35} with Cu, Ni, and Co substitutions for Fe. The crystals are grown by Bridgman's method. The resistivity measurements show that superconductivity disappears with the rate which correlates with the nominal valence of the impurity. From magnetoresistance we evaluate doping effect on the basic superconducting parameters, such as upper critical field and coherence length. We find indications that doping leads to two component superconducting behavior, possibly because of local charge depression around impurities.

2

Influence of Iron Substitutions on the Transport Properties of FeTe_{0.65}Se_{0.35} Single Crystals

88%

Bezusyy V., Gawryluk D., Malinowski A., Berkowski M., Cieplak M.

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vol. 126

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issue 4a

A-76-A-80

EN

We study the ab-plane resistivity and Hall effect in the single crystals of Fe_{1-y}M_yTe_{0.65}Se_{0.35}, where M = Co or Ni (0 ≤ y ≤ 0.21). In case of each dopant two types of crystals, with different crystalline quality, are prepared by Bridgman's method using different cooling rates, fast or slow. The impurities suppress the superconducting transition temperature, T_c, with different rates. T_c reaches zero at markedly different impurity content: only 3 at.% of Ni, and about 14 at.% of Co. In addition, the suppression is somewhat dependent on the crystal cooling rate. The resistivity at the onset of superconductivity rises only weakly with the Co doping, while it increases 10 times faster for Ni. The Hall coefficient R_{H} is positive for Co doping indicating that hole carriers dominate the transport. For Ni R_{H} changes sign into negative at low temperatures for crystals with the Ni content exceeding 6 at.%. The implications of these results are discussed.

3

Magnetic Nature of a Ni Dopant in La_{1.85}Sr_{0.15}CuO_4: Spin-Glass Behavior

76%

Malinowski A., Bezusyy V., Minikayev R., Paszkowicz W., Dziawa P., Syryanyy Y., Sawicki M.

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issue 2

244-248

EN

The magnetic properties of La_{1.85}Sr_{0.15}CuO_4 doped with Ni was investigated in the field up to 5 T and in the temperature range from 2 K to 400 K using both dc and ac techniques. For Ni content larger than 0.05 the system exhibits irreversibility of low-field susceptibility χ(T) below a certain temperature depending on y and a cusp at T_{g} in χ(T) measured after zero-field cooling. The decay of remnant magnetization below T_{g} with time is described by a stretched-exponential function. In accordance with scaling theory, all the χ(T) data for y = 0.50 sample taken in the vicinity of T_{g} at different fields collapse onto two separate curves when plotted as q|t|^{-β} vs. B^2 |t|^{-β - γ}, where q is the spin-glass order parameter, t = (T - T_{g})/T_{g}, and β and γ are the critical exponents. All these features taken together reveal existence of spin-glass phase below T_{g}. Variation of T_{g} with y is linear below y = 0.25 and T_{g} extrapolates to 0 K for y → 0 what strongly suggests that spin-glass phase extends into superconducting region of the phase diagram.

4

From Cuprate to Nickelate: Evolution of the Normal State Properties with Ni from La_{1.85}Sr_{0.15}CuO_4 to La_{1.85}Sr_{0.15}NiO_4

76%

Bezusyy V., Malinowski A., Minikayev R., Paszkowicz W., Dziawa P., Gorzelniak R.

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issue 2

402-405

EN

The influence of Ni doping on the normal-state pseudogap in La_{1.85}Sr_{0.15}CuO_4 is studied by dc magnetic susceptibility measurements, accompanied by X-ray powder diffraction analysis and resistivity measurements. The measurements are carried out on the polycrystalline La_{1.85}Sr_{0.15}Cu_{1-y}Ni_yO_4 samples in the whole doping range from y=0.01 up to y=1. The temperature of pseudogap opening is found to decrease above y=0.05 and to vanish when y exceeds 0.07. At small Ni content, up to y=0.07, the magnetic moment induced by Ni is constant and equal to 0.7 μ_{B} per Ni, while for larger y it increases abruptly and reaches about 1.6 μ_{B} per Ni ion for y = 0.5. The dependence of the normal-state resistivity on temperature evolves smoothly from the metallic-like for small y, to the variable range hopping, described by the Mott law with the exponent 1/4, for samples with y>0.15.

5

Optimization of the Superconducting Properties of Laser Ablated YBa_2Cu_3O_{7-δ} Films on CeO_2-Buffered Sapphire

64%

Abal'osheva I., Zaytseva I., Aleszkiewicz M., Syryanyy Y., Gierłowski P., Abal'oshev O., Bezusyy V., Cieplak M.

Acta Physica Polonica A

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2012

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vol. 121

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issue 4

805-807

EN

We use pulsed laser deposition to grow YBa_2Cu_3O_{7-δ} (YBCO) superconducting films for microwave applications. The films are grown on R-cut sapphire substrates, with CeO_2 buffer layers, which are re-crystallized at high temperature prior to YBCO growth. Using the atomic force microscopy (AFM) and X-ray diffractometry we determine the optimal temperature for recrystallization (1000°C) and the optimal buffer layer thickness (30 nm). The properties of YBCO films of various thickness, grown on the optimized CeO_2 buffer layers, are studied using several methods, including AFM, magnetooptical imaging, and transport experiments. The YBCO film roughness is found to increase with the increasing film thickness, but the magnetic flux penetration in the superconducting state remains homogeneous. The superconducting parameters (the critical temperature and the critical current density) are somewhat lower than the similar parameters for YBCO films deposited on mono-crystalline substrates.

6

Growth and Characterization of YBa_2Cu_3O_{7-δ} Films Deposited by Laser Ablation on CeO_2-Buffered Sapphire

64%

Abal'osheva I., Zaytseva I., Aleszkiewicz M., Malinowski A., Bezusyy V., Syryanyy Y., Gierłowski P., Abal'oshev O., Kończykowski M., Cieplak M.

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vol. 126

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issue 4a

A-69-A-73

EN

In this work we study the growth, by pulsed laser deposition, of YBa_2Cu_3O_{7-δ} (YBCO) films on the CeO_2-buffered R-cut sapphire substrates, with the buffer layer recrystallized prior to the deposition of superconductor. We find that the superconducting critical temperature and the critical current density of the films are very close to similar parameters for the YBCO films grown on lattice-matched single crystalline substrates. It appears that the structural defects in the buffer layer affect the microstructure of YBCO films, resulting in high values of the critical current density, suitable for applications.

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6 Acta Physica Polonica A

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6 Bezusyy V.

4 Cieplak M.

4 Malinowski A.

3 Syryanyy Y.

2 Abal'oshev O.

2 Abal'osheva I.

2 Aleszkiewicz M.

2 Berkowski M.

2 Dziawa P.

2 Gawryluk D.

2 Gierłowski P.

2 Minikayev R.

2 Paszkowicz W.

2 Zaytseva I.

1 Gorzelniak R.