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Size dependence of the magnetic properties of Ni nanoparticles prepared by thermal decomposition method

Xuemin He1, Wei Zhong1*, Chak-Tong Au2 and Youwei Du1

Author Affiliations

1 National Laboratory of Solid State Microstructures and Jiangsu Provincial Laboratory for NanoTechnology, Department of Physics, Nanjing University, Nanjing 210093, China

2 Department of Chemistry, Hong Kong Baptist University, Hong Kong 852, China

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Nanoscale Research Letters 2013, 8:446  doi:10.1186/1556-276X-8-446

Published: 28 October 2013

Abstract

By means of thermal decomposition, we prepared single-phase spherical Ni nanoparticles (23 to 114 nm in diameter) that are face-centered cubic in structure. The magnetic properties of the Ni nanoparticles were experimentally as well as theoretically investigated as a function of particle size. By means of thermogravimetric/differential thermal analysis, the Curie temperature TC of the 23-, 45-, 80-, and 114-nm Ni particles was found to be 335°C, 346°C, 351°C, and 354°C, respectively. Based on the size-and-shape dependence model of cohesive energy, a theoretical model is proposed to explain the size dependence of TC. The measurement of magnetic hysteresis loop reveals that the saturation magnetization MS and remanent magnetization increase and the coercivity decreases monotonously with increasing particle size, indicating a distinct size effect. By adopting a simplified theoretical model, we obtained MS values that are in good agreement with the experimental ones. Furthermore, with increase of surface-to-volume ratio of Ni nanoparticles due to decrease of particle size, there is increase of the percentage of magnetically inactive layer.

Keywords:
Size dependence; Curie temperature; Cohesive energy; Magnetically inactive layer