Study On Magnetocaloric Effect Of Rare Earth Magnetic Refrigerant Materials GdTbCo,DyGdCoSi And Perovskite-Type Oxide

A series of Gd0.6(Tb1-xCox)0.4 (Dy1-xGdx)(Co0.99Si0.01)2 and (Dy1-xGdx)(Co0.98Si0.02)2 alloys have been prepared by arc-melting method. All magnetic measurements were performed using a vibrating sample magnetometer (VSM). The Curie temperature Tc was determined from the temperature dependence of magnetization measured under a field of 0.05T. The magnetization isotherms were measured on field increase in a wide temperature range covering the Curie temperature with different temperature steps. The magnetic entropy changes (â–³Sm) as a function of the temperature in magnetic field (1.5T or 1.0T) for these alloys have been obtained approximately from the isothermal magnetization through numerical calculation. The results from research suggested that by means of changing the content of some components, the Curie points of these samples obtained obvious improvement and the magnetic entropy changes still could maintain impressive magnitude. Considering the practicability, we can use these alloys to make complex materials that are suitable for the Ericsson cycle. So these alloys are suitable candidates as magnetic refrigerant materials near room temperature.In consideration of the study on perovskite-type oxide in Nanjing University, the nano-La0.62Ce0.05Ca0.33MnO3 and La0.67Ca0.33MnO3 were prepared by sol-gel in this paper. Their microstmcture has been analyzed by XRD, the magnetic capability has been researched. The experimental results showed that higher the thermal annealing temperature and longer the thermal annealmg time, smaller the particle size, then lower the Curie temperature and smaller the magnetic entropy changs. At the same time, we found that the magnetic entropy changs rised twice times and the Curie temprature was improved after a few Ce atoms substiting for La atoms.This paper has carried on the proper discussion about whether Maxwell's relationship could calculate the magnetic entropy changes of the first-order phase transition. The results from analysing indicated that Maxwell's relationship could calculate above magnetic entropy changes, and it could give more reasonable results in the actual system than Clausius-Clapeyron formula.Finally, based on formerly researches, a detailed analyse was made on the effects of the properties of magnetic-phase transition on the MCE in some typical magnetic refrigerant materials, then some conclusions were presented.