Investigation On Magnetocaloric Properties Of Gd_1-xM_x(M=V,Ti) And Gd_0.97-yDy_yV_0.03 Alloys

Recently, Gadolinium metal has been the most thoroughly studied material for its MCE, but the price of Gd is very expensive, the curie temperature of Gd is fixed, as a result, its working region is quite narrow. Considering the various requirements for practical application, it is necessary to search for some magnetic refrigerants which MCE properties are same as(or higher than) Gd with different Curie temperatures (T_c), In this thesis, we investigated the binary and ternary Gd-based solid solution alloys by adding nonferrous metal elements(V,Ti), and heavy rare-earth element (Dy) to estimate their magnetocaloric properties.The author of this paper researched on the phase structure, the curie temperature, adiabatic temperature changes and magnetic entropy changes of Gd_1-xM_x(M=V,Ti) alloys and Gd_0.97-yDy_yV_0.03(y=0.1,0.2,0.3) alloys that were prepared by arc melting in an argon atmosphere.X-ray diffraction patterns show that all Gd_1-xM_x(M=V,Ti) alloys retain the phase structure of pure Gd. Compared with the pure Gd, the Curie temperature of these alloys decrease slightly. The adiabatic temperatures changes(ΔT_ad)of these alloys at Curie points increase firstly and decrease latter with increasing x in a field change 0～1.4T. The adiabatic temperatures changes of Gd_1-xTi_x alloys is, when x=0.09, 102.4% of that of Gd. The adiabatic temperatures changes of Gd_1-xV_xalloys is, when x=0.03, 106% of that of Gd; The magnetic phase transitions from paramagnetic state to the magnetically ordered state in Gd_1-xV_x alloys are the second order type. The magnetic entropy changes of Gd_1-xV_x alloys at Curie points increase firstly and decrease latter with increasing x in a field change 0～2T, the best magnetic entropy changes of Gd_1-xV_x alloys at Curie points increase is 5.19J/kg.K, when x=0.03, 103.8% of that of Gd; furthermore, the refrigeration capacities are larger than Gd.The ternary Gd_0.97-yDy_yV_0.03(y=0. 1,0.2,0.3) alloys were made on the basis of above binary Gd-based solid solution. X-ray diffraction patterns show that these alloys are all the hexagonal lattice structure as same as Gd; Their curie temperatures can be tuneable with an experiential formula, Tc=291.38-104.9y. The adiabatic temperatures changes(ΔT_ad)of these alloys at Curie points decrease firstly and increase latter with increasing y in a field change 0～1.4T. The best adiabatic temperatures change of Gd_0.97-yDy_yV_0.03 alloys is 2.65K when y=0.1, 106.85% of that of Gd; The magnetic entropy changes of Gd_0.97-yDy_yV_0.03 alloys at curie points increase firstly and decrease latter with increasing y in a field change 0～2T. When y=0.1, the magnetic entropy changeΔS_M is 99.2% of Gd, cooling capacity q is 104.6% of Gd; when y=0.2,ΔS_M is 106.6% of Gd, q is 99.5% of Gd.Above works reveal that magnetocaloric properties of Gd_0.91Ti_0.09,Gd_0.97V_0.03, Gd_0.87Dy_0.1 V_0.03,and Gd_0.77Dy_0.2V_0.03 are the best in Gd_1-xM_x(M=V,Ti) alloys and Gd_0.97-yDy_yV_0.03(y=0.1,0.2,0.3) alloys. These suggest that these alloys are promising candidates for magnetic refrigerants which may be used in the active magnetic regeneratior near room temperature in low magnetic fields.