Influence of size distribution on the magnetocaloric effect of superparamagnetic gold-magnetite nanocomposite

The magnetocaloric effect of the superparamagnetic nanocomposite composed of magnetite grains isolated by gold was investigated as a function of the size distribution width. The magnetic entropy change DeltaS was evaluated by applying Maxwell's relation to the magnetization data sets measured at various temperature and applied field. The size distribution was evaluated by the TEM observation, showing that the average sizes were from 4.6 to 7.4 nm and the geometric standard deviations sigma(g) from 1.32 to 1.59. Thus evaluated DeltaS was found to increase with decreasing sigma(g), demonstrating our previous anticipation that the narrow size distribution would much enhance the magnetocaloric effect of the superparamagnetic nanocomposite material. The DeltaS was several times larger than that of our previous nanocomposite composed of gamma-Fe2O3 and silver. (C) 2003 Elsevier B.V. All rights reserved.