Study On The Microstructure And Magnetocaloric Effects Of Gd-Zn-Mn And Gd-Mn-Si Alloys

Magnetic refrigeration can be achieved by magnetocaloric effect of magnetic materials.Compared with the gas compression refrigeration,it has no noise,no pollution and is a green refrigeration technology,which has great developing potential.Gd and Gd based binary alloys which at near room temperature have great magnetocaloric effect but they still cannot satisfy the requirement of room temperature refrigeration technology.This paper aimed at Gd-Mn and Gd-Zn binary alloys,which have been prepared by using vacuum smelting with nominal compositions of Gd70MnxZn30-x(x=3,5,7,9,11)and Gd80MnxSi20-x(x=3,5,7,9,11).The following work has been carried out:1.The Miedema model is used to calculate the formation energies of Gd-Zn,Gd-Si and Gd-Mn.The formation energy of Gd5Si3 phase can be less than that of GdMn2 phase,and the formation energy of Gd Mn2 phase can be less than the formation energy of GdZn phase.2.It studied the Curie temperatures,magnetic entropy change,Arrott plots,adiabatic temperature and microstructure of Gd70MnxZn30-x(x=0,3,5,7,9,11)alloys.The experimental results showed that,when the Mn increases,the Curie temperature of Gd70MnxZn30-x(x=3,5,7,9,11)alloys is rising and then stablized,and the magnetic entropy of Gd70MnxZn30-x(x=3,5,7,9,11)alloys is rising and then stablized,and the adiabatic temperature of Gd70MnxZn30-x(x=3,5,7,9,11)alloys is rising first and then decreaing.According to the Arrott curve,the alloys have second-order phase transformation.The increasing of Mn element could refine GdZn grain and also can slow down the declining process of the magnetization process.3.It studied the Curie temperatures,magnetic entropy change,Arrott plots,adiabatic temperature and microstructure of Gd80SixMn20-x(x=3,5,7,9,11)alloys.With the increasing of Si content,the Curie temperature of Gd80SixMn20-x(x=3,5,7,9,11)alloys is rising and then stablized,and magnetic entropy change of Gd80SixMn20-x(x=3,5,7,9,11)alloys is increased and then decreased.Through the Arrott curve,it is known that the samples have second-order phase transformation.According to the analysis of M-T plots,Si element can reduce the sensitivity of the alloy to temperature which makes the response weaker.In conclusion,Gd70MnxZn30-x(x=0,3,5,7,9,11)alloys and Gd80SixMn20-x(x=3,5,7,9,11)alloys,can improve the Curie temperatures.Therefore Gd70MnxZn30-x(x=0,3,5,7,9,11)alloys and Gd80SixMn20-x(x=3,5,7,9,11)alloys are potential materials for room temperature refrigeration.