The research on the fabrication and magnetic property of GdAl2 nanoparticles

• Main Authors: Shin-Hong Zheng, 鄭信宏
• Other Authors: 王昌仁
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/72456307577177257141

碩士 === 東海大學 === 物理學系 === 97 === Bulk GdAl2 is good candidate for application of magnetocaloric effect. Recently, some studies predicated a larger cryogenic magnetocaloric effect can be found in nano-structure GdAl2. On the contrary, the magnetization was reduced in CeAl2 nanoparticles. In this report, the good quantity GdAl2 nanoparticles were fabricated by electron discharge machine (EDM) to verify the magnetic behaviors of GdAl2 nanoparticles. The X-ray diffraction pattern shows that the GdAl2 nanoparticles are single-phase. The nanoparticles with size about 20~40nm and a few μm-particles can be observed in our specimen by HRTEM. Two nano-scale specimens for this research exhibit ferromagnetic behavior with ferromagnetic temperature near 170 K. Below 170 K, the superparamagnetic behavior coming from nanoparticles can be recognized by magnetic susceptibility for these specimens. The smaller Curie constant of nanoparticles as compared to that of bulk can be obtained the Curie-Weiss fit about 170 K. This imply that the concentration of magnetic Gd3+ decreases when the size decrease. The behavior is similarly to the GdAl2 nanoparticles. The magnetic entropy change -ΔS were calculated from variable magnetic field M-H curve for variable temperature. The maximum value of -ΔS is near TC for bulk GdAl2. But for GdAl2 nanoparticles, the magnetic entropy was suppressed neat TC and increased with temperature decreasing below TC. The behavior is similarity to the GdAl2/Al2O3 nanocapsules.