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W. Cheikh-Rouhou Koubaa M. Koubaa A. Cheikhrouhou 《Journal of Alloys and Compounds》2009,470(1-2):42-46
We investigate the effect of potassium doping on the structural, magnetic and magnetocaloric properties of La0.7Sr0.3−xKxMnO3 (x = 0.05, 0.1, 0.15 and 0.2) powder samples. Our polycrystalline compounds were synthesized using the solid-state reaction at high temperature. X-ray diffraction characterizations showed that all our studied samples crystallize in the distorted rhombohedral system with space group. With increasing potassium content, the unit cell volume exhibits a broad maximum around x = 0.15. Magnetization measurements versus temperature showed that all our samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature TC is found to decrease from 365 K for x = 0 to 328 K for x = 0.2 as well as the saturated magnetization Msp which shifts from 3.68 μB/Mn for x = 0 to 3.05 μB/Mn for x = 0.2. The critical exponent γ defined as Msp (T) = Msp(0)[1−(T/TC)]γ is found to remain almost constant and equal to 0.33 for all our samples. The maximum of magnetic entropy changes |ΔSmax| of La0.7Sr0.3−xKxMnO3 for x = 0.05 and 0.15 is found to be respectively, 1.37 and 1.2 J kg−1 K−1 under a magnetic field change of 1 T. 相似文献
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X.C. Zhong P.F. TangZ.W. Liu D.C. ZengZ.G. Zheng H.Y. YuW.Q. Qiu M. Zou 《Journal of Alloys and Compounds》2011,509(24):6889-6892
Amorphous Gd68−xNi32+x (x = −3, 0, 3) ribbons were prepared by melt-spinning method. The crystallization onset temperatures Tx1 for Gd68−xNi32+x amorphous ribbons with x = −3, 0, and 3 are 561, 568, and 562 K, respectively. All the samples undergo the second-order magnetic transition at temperatures between ∼122 (x = −3 and 3) and 124 K (x = 0). The Curie temperature TC does not change with the composition significantly. The maximum isothermal magnetic entropy changes (−ΔSM)max of Gd71Ni29, Gd68Ni32, and Gd65Ni35 amorphous ribbons for a magnetic field change of 0-5 T were 9.0, 8.0, and 6.9 J kg−1 K−1, respectively. Large values of the refrigerant capacity (RC) were obtained in these ribbons. For example, Gd71Ni29 amorphous ribbon has a maximum RC value of 724 J kg−1. Large magnetic entropy change and RC values together with high stability enable the Gd71Ni29 amorphous alloy a competitive candidate among the magnetic refrigeration materials working at temperatures near 120 K. 相似文献
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E. Ta?arkuyu A. Co?kunA.E. Irmak S. AktürkG. Ünlü Y. Samanc?o?luA. Yücel C. Sar?kürkçüS. Aksoy M. Acet 《Journal of Alloys and Compounds》2011,509(9):3717-3722
We investigate the effect of sintering temperature on the structural and magnetic properties of La1.4Ca1.6Mn2O7 double perovskite manganite compound prepared by the sol-gel route. Three sintering temperatures (1273, 1473 and 1673 K) are utilized for the heat treatment. Regardless of the sintering temperature, the tetragonal crystal structure with the I4/mmm space group is stable. However, a reduction in a and an increase in c lattice parameters along with a significant increase in crystallite-size occur on increasing the sintering temperature. This is also accompanied by the growth of grains. Grain-growth and changing crystallite-sizes account for the changes in magnetization, Curie temperature and magnetic entropy-change values. As the sintering temperature increases from 1273 to 1673 K the Curie temperature increases from 225 to 268 K and the magnetic entropy-change increases from 0.58 to 3.1 J kg−1 K−1 respectively. 相似文献