觀察不同氧化程度的鎳奈米微粒，探討其氧化殼層厚度對樣品磁性影 響。經過25 天的氧化過程，4.6 nm 的鎳奈米微粒氧化殼層由0.13 nm 增加 至0.27 nm，而2 nm 的鎳奈米微粒氧化殼層由0.16 nm 增加至0.3 nm，經 由磁性量測我們觀察到二個現象。 1. 經由場冷(field-cooled)及零場冷 (zero-field-cooled) 過程之磁化強 度隨溫度變化圖得知，隨著氧化殼層增加，4.6nm 樣品阻隔溫度( B T )升高 了大約50K 而2nm 的樣品升高了20K。此二樣品FC 曲線在低溫皆有轉折， 推測在此溫度氧化殼層發生相變所造成。 2. 平均粒徑4.6 nm 之鎳奈米微粒隨著氧化層厚度的增加，使得矯頑場 逐漸增強，且在溫度為40K 左右，矯頑場數值達到極大，矯頑場極大值由 35 Oe 上升到53 Oe，增強了1.5 倍左右，但殘留磁化強度對不同溫度之變 化圖則無明顯差異。然而2 nm 的鎳奈米微粒隨著氧化層增厚時，樣品矯頑 場有明顯增強效益，在溫度為20K 左右，其極大值由30 Oe 增強至113 Oe， 增強的輻度為4 倍左右，殘留磁化強度極大值由4.47 emu/g 提升至7.64 emu/g，且出現極大值之溫度由1.8K 升高至20K。 We report a systematic investigation of the magnetic properties of Ni nanoparticles after three extents of oxidation. First we prepared two sizes samples by PVD(physical vapor deposition). Then the samples were oxidized by 25 days. A series of copper nanoparticles were oxided to form core-shell structure. We find that TB of the core-shell structure Ni /NiO(4.6nm) increases 50K, the TB of the other one sample(2nm) increases 20K. When temperature is at 40 K, all of the sample have a peak in the field-cooled (FC) temperature-dependent magnetization .When the NiO shell is wider, the phenomenen is distincter. By the NiO shell thickness from 0.13nm to 0.27nm, the maximum coercivity of the sample(4.6nm) increases 1.5 times. In the same, by the NiO shell thickness from 0.16nm to 0.3nm the the maximum coercivity of the other sample(2nm) increased 4 times.
