Size and shape effects on magnetic properties of Ni nanoparticles--颗粒学报PARTICUOLOGY

He, X., & Shi, H. (2012). Size and shape effects on magnetic properties of Ni nanoparticles. Particuology, 10(4), 497–502. https://doi.org/10.1016/j.partic.2011.11.011

Size and shape effects on magnetic properties of Ni nanoparticles

Xuemin He, Huigang Shi^*

Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, China

10.1016/j.partic.2011.11.011

Volume 10, Issue 4, August 2012, Pages 497-502

Received 1 July 2011, Revised 14 November 2011, Accepted 21 November 2011, Available online 22 March 2012.

E-mail: shihuig@lzu.edu.cn; zspohexuemin@163.com

Highlights

► Size- and shape-controlled Ni nanoparticles are prepared by thermal decomposition of nickel acetylacetonate in oleylamine.

► The change trend of coercivity can be attributed to the competition between size effect and shape anistropy.

► The Curie temperature T_c is 593, 612, 622, 626 and 627 K for the 24, 50, 96, 165 and 200 nm Ni nanoparticles, respectively.

Abstract

Pure Ni nanoparticles ranging in size from 24 to 200 nm are prepared via thermal decomposition of nickel acetylacetonate in oleylamine. The as-prepared Ni particles change from spherical to dendritic or starlike with increasing precursor concentration. The particles are stable because the organic coating occurs in situ. Magnetic measurement reveals that all the Ni nanoparticles are ferromagnetic and show ferromagnetic–paramagnetic transitions at their Curie points. The saturation magnetization M_s is size-dependent, with a maximum value of 52.01 and 82.31 emu/g at room temperature and 5K, respectively. The coercivity decreases at first and then increases with increasing particle size, which is attributed to the competition between size effect and shape anisotropy. The Curie temperature T_c is 593, 612, 622, 626 and 627K for the 24, 50, 96, 165 and 200 nm Ni nanoparticles, respectively. A theoretical model is proposed to explain the size-dependence of Ni nanoparticle Curie temperature.

Graphical abstract

Keywords

Precursor concentration; Size effect; Shape anisotropy; Curie temperature

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