Magnetic and magnetocaloric properties of LaCaMnO and FeCrCuNbSiB compounds

Recently, perovskite manganites A1-xA?xMnO3 (where a is a trivalent rare earth ion such as La and A? is a divalent ion such as Ca) have become a subject attracting of investigation due to the colossal magnetoresistance (CMR) and large magnetocaloric effect (MCE). The MCE is an isothermal magnetic entropy change or an adiabatic temperature change of a magnetic material caused by an applied magnetic field. This physical phenomenon has been basis of magnetic refrigeration technology. This thesis presents results of structural, magnetic, magnetocaloric and magnetoresistive properties of Fe74-xCrxCu1Nb3Si13BB9 (x = 14 and 17) amorphous alloys and some manganites. The manganites studied in this work have a perovskite structure with the chemical composition of La2/3Ca1/3MnO3, La0.67-xBixCa0.33MnO3 (x=0.05, 0.1 and 0.2), La0.67Ca0.33Mn1-xVxO3 (x=0, 0.03, 0.06, 0.1, 0.15 and 0.25) and La0.67Ca0.33Mn1-xBxB O3 (x=0, 0.05, 0.1, 0.2 and 0.3) . The samples were prepared by the conventional solid-state reaction and sol-gel method. The magnetocaloric effect of the all samples was measured by means of magnetization measurements. All the samples iii showed a magnetocaloric effect in the vicinity of Tc. The effect of the doping concentration of the elements with different ionic radius on the magnetic and magnetocaloric properties has been examined. The magnetism and conductivity properties of manganites were discussed on the basis of Double exchange (DE) mechanism. KEYWORDS : Perovskite Manganites, Magnetocaloric Effect, Magnetic Refrigeration, Magnetoresistance, Amorphous Ferromagnetic Alloys