This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis whe...This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they trans-form from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.展开更多
Phase transition process and magnetic entropy change -Delta S of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied. Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural an...Phase transition process and magnetic entropy change -Delta S of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied. Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural and magnetic transitions and transform from ferro-magnetic martensitic phase to paramagnetic austenitic phase during heating. Under a field of 2 T, the maximum magnetic entropy change -Delta S-M of Ni55.2Mn18.6Ga26.15Gd0.05 alloy was 7.7 J/kg.K at 317 K during heating and 8.6 J/kg.K at 314 K during cooling while it was 11.8 J/kg.K at 317 K in Ni55.2Mn18.6Ga26.05Gd0.15 alloy during heating.展开更多
With the addition of Gd, the Ni56Mn18.8Ga24.5 Gd0.7 alloy exhibits non-modulated martensite phase at room temperature. From the illustration of Gd microstructure, it can be found that Gd exists along the subgrain boun...With the addition of Gd, the Ni56Mn18.8Ga24.5 Gd0.7 alloy exhibits non-modulated martensite phase at room temperature. From the illustration of Gd microstructure, it can be found that Gd exists along the subgrain boundaries. Hence, the crystalline size decreases and the mechanical properties improve. At-susceptibility results show that Ni56Mn18.8Ga24.5 Gd0.7 alloy still undergoes simultaneous structural and magnetic transitions and transforms from ferromagnetic martensitic phase to paramagnetic austenitic phase with increasing temperature. The maximum magnetic entropy change is 13.4 J· （kg·K） ^-1 under 1.9 T field at 338 K. The giant magnetocaloric effect found in Ni56Mn18.8Ga24.5 Gd0.7 alloy is attributed to the concurrently occurring first-order structural- and magnetic-phase transitions.展开更多
基金supported by the National Basic Research Program of China (Grant No.2006CB601101)the National High Technology Research and Development Program of China (Grant No.2007AA03Z440)the National Natural Science Foundation of China(Grant No.50731007)
文摘This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they trans-form from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.
基金Project supported by the National Science Foundation of Chinathe National Basic Research Program of China and Institute of Physics,Chinese Academy of Sciences
文摘Phase transition process and magnetic entropy change -Delta S of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied. Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural and magnetic transitions and transform from ferro-magnetic martensitic phase to paramagnetic austenitic phase during heating. Under a field of 2 T, the maximum magnetic entropy change -Delta S-M of Ni55.2Mn18.6Ga26.15Gd0.05 alloy was 7.7 J/kg.K at 317 K during heating and 8.6 J/kg.K at 314 K during cooling while it was 11.8 J/kg.K at 317 K in Ni55.2Mn18.6Ga26.05Gd0.15 alloy during heating.
基金Project supported bythe National Natural Science Foundation of China (50571008) National Basic Research Programof China(2006CB601101)
文摘With the addition of Gd, the Ni56Mn18.8Ga24.5 Gd0.7 alloy exhibits non-modulated martensite phase at room temperature. From the illustration of Gd microstructure, it can be found that Gd exists along the subgrain boundaries. Hence, the crystalline size decreases and the mechanical properties improve. At-susceptibility results show that Ni56Mn18.8Ga24.5 Gd0.7 alloy still undergoes simultaneous structural and magnetic transitions and transforms from ferromagnetic martensitic phase to paramagnetic austenitic phase with increasing temperature. The maximum magnetic entropy change is 13.4 J· （kg·K） ^-1 under 1.9 T field at 338 K. The giant magnetocaloric effect found in Ni56Mn18.8Ga24.5 Gd0.7 alloy is attributed to the concurrently occurring first-order structural- and magnetic-phase transitions.
