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2 Acta Physica Polonica A

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Structure and Transport Properties of La_{0.75-x}RE_xCa_{0.25}MnO_3 (RE = Gd, Dy, Ho; 0≤ x≤0.75) Manganites

100%

Drozd V. , Pękała M. , Kovac J. , Skorvanek I. , Szymański M. , Nedilko S.

Acta Physica Polonica A

2004

tom 106

nr 5

751-758

Structure and transport properties have been studied for a series of La_{0.75-x}RE_xCa_{0.25}MnO_3 manganites with heavy rare earth ions of Gd, Dy, Ho substituting La with x=0, 0.10, 0.25, 0.50, and 0.75. Polycrystalline samples were prepared by the carbonate precipitation route. The oxygen content was determined by the iodometric titration. The X-ray investigations carried out by the powder method show that the unit cell volume gradually decreases and orthorhombic distortion of the lattice increases with rising RE content. Below the room temperature the electrical resistivity is of the semiconducting type for all the samples studied. Electrical resistivity vs. temperature dependences were analyzed within different models: simple thermal activation, Mott's variable range hopping, adiabatic, nonadiabatic, and bipolaron. The Curie temperatures of Gd, Dy, and Ho substituted manganites determined from magnetization measurements show that at 280 K all the samples are in the paramagnetic phase. The increasing RE fraction reduces magnetization at 4 K as compared to La_{0.75}Ca_{0.25}MnO_3.

Thermomagnetic Properties of LaFe_{11.0}Co_{0.8}(Si_{1-x}Al_{x})_{1.2} (x=0, 0.6) Alloys

84%

Gębara P. , Pawlik P. , Skorvanek I. , Marcin J. , Pawlik K. , Przybył A. , Wysłocki J. , Szwaja M. , Filipecka K.

Acta Physica Polonica A

2014

tom 126

nr 1

166-167

In the present work, Curie temperature, refrigeration capacity and cooling power of the LaFe_{11.0}Co_{0.8}(Si_{1-x}Al_{x})_{1.2} (where x=0, 0.6) alloys, are investigated. The value of Curie temperature was found to be 280 and 290 K for x=0 and 0.6, respectively. The determined values of cooling power (RCP) and refrigeration capacity (RC) differ only slightly for both investigated alloys. The maximum values of RCP and RC obtained under the change of external magnetic field from 0 to 5 T are 433 J/kg (for x=0) and 290 J/kg (for x=0.6), respectively.