Synthesis, structure and magnetic properties of DyAl2 nanoparticles

Magnetic properties of Dy nanoparticles and Al2O3-coated Dy nanocapsules

“…The -DS m Fig. 7 Temperature dependence of the magnetic-entropy change of a Dy nanoparticles and b Al 2 O 3 -coated Dy nanocapsules between 7.5 and 197.5 K in a field change from 1 to 5 T. The insets show the magnetic isotherms from 5 to 205 K, obtained in a ZFC measurement value of Dy nanocapsules exceeds 2 Jkg -1 K -1 the in the range from 7.5 to 105 K at DB = 4T, which is broader than that reported previously in superparamagnetic nanoparticles/nanocapsules (Liu et al 2008a(Liu et al , b, 2009a(Liu et al , b, 2010Ma et al 2007Ma et al , 2008Zhang et al 2006;Nelson et al 2003). The wide working-temperature range mainly comes from the coexistence of the SPM and the SPM-AFM transition in Dy nanocapsules.…”

“…The variation of the magnetization of the nanoparticles/nanocapsules is determined by the applied field Zeeman energy, thermal agitation energy k B T, anisotropy energy barrier, and weaker interaction energy between the particles, which have different effects on the rotation of the moments, respectively. The relationship and balance among these four kinds of energies in superparamagnetic nanoparticles/nanocapsules have been studied in detail in our previous study (Liu et al 2008a(Liu et al , b, 2009a(Liu et al , b, 2010Ma et al 2007Ma et al , 2008Zhang et al 2006). When the temperature and applied field are changed, the Zeeman energy and k B T will help to overcome the hindrance of the anisotropyenergy barrier and the weak interaction energy to change the orientations of the large amount of magnetic moments from a high moment density in the Dy nanoparticles/nanocapsules, which can generate a large change of magnetic order and lead to a large -DS m .…”

“…Dy nanoparticles/nanocapsules were synthesized by a modified arc-discharge process similar to the one used in our previous study (Zhang 2007;Liu et al 2008aLiu et al , b, 2009aLiu et al , b, 2010Geng et al 2003;Zhang et al 2006;Ma et al 2007Ma et al , 2008Si et al 2004). Master DyAl alloy was prepared by arc melting Dy and Al bulks of 99.9 wt% purity under a high purity argon atmosphere.…”

“…Therefore, it is significant to search an easy and substrate-free fabrication technique, which can prevent RE nanoparticles from severe oxidization. As a well-known method for producing nanoparticles/ nanocapsules, the arc-discharge technique has been widely used in the last decade (Zhang 2007;Liu et al 2008aLiu et al , b, 2009aGeng et al 2003;Zhang et al 2006;Ma et al 2007;Si et al 2004). Nanocapsules, which are normally composed of a core and a shell in the size of nanometer that are made of different materials, are excellent for preventing the core from further oxidization (Zhang 2007).…”

“…Nanocapsules, which are normally composed of a core and a shell in the size of nanometer that are made of different materials, are excellent for preventing the core from further oxidization (Zhang 2007). In the previous studies, we successfully introduced ceramics Al 2 O 3 as the shell and fabricated Al 2 O 3 -coated REAl 2 (RE = Dy, Gd, Ho, and Tb) compound nanocapsules by a modified arc discharge technique on the basis of evaporation pressures (Liu et al 2008a(Liu et al , b, 2009aZhang et al 2006;Ma et al 2007). Recently, Gd and Dy nanocapsules, DyCo 2 and HoCo 2 nanoparticles were synthesized by the arc discharge technique and their magnetic properties were investigated (Liu et al 2009a(Liu et al , b, 2010Si et al 2004;Ma et al 2007).…”