Magnetic properties and large cryogenic low-field magnetocaloric effect of HoCo2 nanoparticles without core/shell structure

Magnetic properties of Dy nanoparticles and Al2O3-coated Dy nanocapsules

“…7a, in which the increment of the temperature is 10 K. As shown in Fig. 7a, the value of -DS m increases monotonously with decreasing temperature, which is similar with the results of SPM GdAl 2 , TbAl 2 , HoAl 2 , Gd, DyCo 2 , HoCo 2 nanocapsules/ nanoparticles, due to a large magnetization change in low temperatures at a given field change (Liu et al 2008a(Liu et al , b, 2009a(Liu et al , b, 2010Ma et al 2007Ma et al , 2008. At 7.5 K, -DS m reaches a value of 5.16 J kg -1 K -1 in a field change from 1 to 5 T, which is smaller than those of the systems mentioned above, due to the smaller magnetization reduced by serious oxidation in Dy nanoparticles.…”

“…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.…”

“…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). These nanoparticles/nanocapsules can be stable in air without any special protection and they also exhibit large cryogenic magnetocaloric effect (MCE) induced by superparamagnetism (SPM), which can be applied for the magnetic refrigeration at low temperatures (Liu et al 2009a(Liu et al , b, 2010Ma et al 2007Ma et al , 2008.…”

“…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). These nanoparticles/nanocapsules can be stable in air without any special protection and they also exhibit large cryogenic magnetocaloric effect (MCE) induced by superparamagnetism (SPM), which can be applied for the magnetic refrigeration at low temperatures (Liu et al 2009a(Liu et al , b, 2010Ma et al 2007Ma et al , 2008. Utilization of magnetic refrigeration depends on the development of materials with sufficiently large changes of magnetic entropy at sufficiently low applied fields.…”

Giant reversible magnetocaloric effect in flower-like β-Co(OH)2 hierarchical superstructures self-assembled by nanosheets

“…Currently, there is a great deal of interest in utilizing the magnetocaloric effect (MCE) as an alternate technology for refrigeration, replacing the common gas-compression expansion technology, due to higher efficiency and environmental concerns [1][2][3][4][5][6][7][8][9][10][11] . An ideal material for magnetic refrigeration should be composed of relatively inexpensive raw materials, have a high MCE demonstrated by a high change in magnetic entropy (ΔS M ) and a high adiabatic temperature change, and have little or no thermal/magnetic hysteresis 1,8 .…”