Investigation On Magnetocaloric Properties Of Gd_0.6Dy_0.4Co_2-xAl_x And Gd_0.55Dy_0.45Co_2-xAl_x Alloys

Recently, GdCo₂ and DyCo₂ which have a cheap price have been come to people's notice. The curie temperature of GdCo₂, which magnetic phase transition is second order transition, is much higher than room temperature, and magnetic entropy change of alloy is relative low. Otherwise, the curie temperature of DyCo₂, which magnetic phase transition is first order transition, is much lower than room temperature, and magnetic entropy change of alloy is relative high. Neither of them is fit to be a magnetic refrigerant material in room temperature. For making capital out of advantages of GdCo₂ and DyCo₂, and preparing alloys which curie temperature are near room temperature, magnetic entropy change is high enough to be used in low magnetic fields, and have a cheap price, the author of this paper prepared two series of Gd_0.6Dy_0.4Co_2-xAl_x and Gd_0.55Dy_0.45Co_2-xAl_x(X=0,0.05,0.1,0.15) alloys by substituting Dy for Gd in GdCo₂, and Al for Co by arc melting in an argon atmosphere. The casting samples were then heat-treated in 4 days and 7 days at 900℃respectively. The properties of two series alloys with casting and heat-treated conditions were checked by SQUID quantum magnetometer, XRD, SEM, the adiabatic temperature changes measurement system, to reveal that addition of Al and Dy how to influence the phase structure, adiabatic temperature changes, the curie temperature and magnetic entropy changes of casting and heat-treated GdCo₂ alloys.X-ray diffraction patterns at room temperature showed that Gd_0.6Dy_0.4Co_2-xAl_x and Gd_0.55Dy_0.45Co_2-xAl_x alloys of casting and heat-treated in 4 days were all belong to crystal structure of GdCo₂ and GdCo₃, and these alloys of heat-treated in 7 days were belong to crystal structure of GdCo₂ only. In a field change 0-1.4T, with content of Al increasing, the peak of adiabatic temperatures changes (â–³T_ad) of Gd_0.6Dy_0.4Co_2-xAl_x and Gd_0.55Dy_0.45Co_2-xAl_x alloys of casting and heat-treated in 7 days all decreased, the peak of adiabatic temperatures changes (â–³T_ad) of these alloys heat-treated in 4 days decreased firstly and increased latter. When x=0.1, the peak of adiabatic temperatures changes of alloy was the smallest one. When content of Al is same, to Gd_0.6Dy_0.4Co_2-xAl_x and Gd_0.55Dy_0.45Co_2-xAl_x alloys, there is identical regulation that the peak of adiabatic temperatures changes of alloys heat-treated in 7 days were higher than alloys heat-treated in 4 days, the peak of adiabatic temperatures changes of alloys heat-treated in 4 days were higher than casting alloys. In addition, when content of Al is same and at the same condition, the peak of adiabatic temperature changes of Gd_0.6Dy_0.4Co_2-xAl_x alloys were higher than Gd_0.55Dy_0.45Co_2-xAl_x alloys. With content of Al increasing, the curie temperature of two series alloys in different conditions increased firstly and decreased latter. When x=0.1, the curie temperature of alloys was the highest one. This result is corresponded with forecasting regulation.Because of heat treatment 4 days and 7 days at 900℃, the peak of adiabatic temperature changes of Gd_0.6Dy_0.4Co_2-xAl_x and Gd_0.55Dy_0.45Co_2-xAl_x alloys increased. Particularly, after heat-treated in 7 days, because crystal structure of Gd_0.6Dy_0.4Co_2-xAl_x(X=0,X=0.1) alloys changed from double-phases to single-phase and element distribution of alloys were more uniform basically, magnetic entropy changes of alloys also kept high value in low magnetic fields 1Tesla, magnetic entropy changes of alloys were 53.2% and 33.1% higher than casting alloys respectively.Above works showed that it could make the curie temperature of alloys change near room temperature by changing content of Dy and Al in GdCo₂ alloy. In addition, adding Dy and Al to alloys could make cost decreasing, and not change second order transition of GdCo₂ alloy. In this research, the curie temperature of Gd_0.6Dy_0.4Co₂ alloy is near room temperature, the alloy with a cheap price exhibits high magnetic entropy change in low magnetic fields. These suggested that this alloy is a promising candidate for magnetic refrigerants, which may be used in the active magnetic refrigerating materials near room temperature in low magnetic fields.