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2 Acta Physica Polonica A

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Comparison of Flux Pinning in Single Crystals and Melt-Textured YBa_{2}Cu_{3}O_{7-x}

100%

Puźniak R. , Wiśniewski A. , Baran M. , Zhou L.

nr 3

373-376

Flux pinning properties of single crystals and melt-textured samples of YBa_{2}Cu_{3}O_{7-x} were studied for external magnetic field oriented parallel and perpendicular to the CuO_{2} planes (ab-planes). For H ∥ ab vortex behaviour is mainly determined by a very effective intrinsic pinning mechanism. The irreversibility line is located in the region of higher fields and temperatures in comparison with the irreversibility line for H ⊥ ab. In a single crystal for H ⊥ ab, we observed an increase in the critical current density j_{c} with magnetic field - the so-called "fishtail effect" - in a very broad temperature range. For H ∥ ab, this effect is observed only at temperatures close to T_{c}, when the intrinsic pinning is much weaker.

Magnetic and Structural Study of Mn_{1.15}Fe_{0.85}P_{1-x}Ge_{x} (0.25 < x < 0.32) Magnetocaloric Compounds Prepared by Arc Melting

63%

Hawelek L. , Wlodarczyk P. , Zackiewicz P. , Polak M. , Kaminska M. , Puźniak R. , Radelytskyi I. , Kolano-Burian A.

nr 1

76-80

Recently, room temperature magnetocaloric materials increasingly attracted attention in the development of magnetic refrigerators. In this paper, an effect of P/Ge substitution on the magnetic phase transition in the series of Mn_{1.15}Fe_{0.85}P_{1-x}Ge_{x} (0.25 < x < 0.32) magnetocaloric compounds prepared by the arc melting technique and subsequent homogenization process has been studied. Calorimetric and magnetization results show that the temperature of structural phase transition coincide with the Curie temperature and fall within the temperature range 270-355 K. The magnetic entropy change reaches the maximum value for the compound with x=0.28 and equals to 32 J/(kg K) for the magnetic field change of 5 T. The adiabatic temperature change for the same sample, measured using magnetocalorimeter, is equal to 1.2 K for the magnetic field change of 1.7 T. It was found that the increase of Ge content in the sample causes weakening of first order magnetic transition, which is manifested by the lowering difference in transition temperature measured in two zero-field-cooling and field-cooled-cooling regimes.