Simple enhancement of the magnetocaloric effect in giant magnetocaloric materials

A simple method of enhancing the magnetocaloric effect (MCE)) in ferromagnetic materials is described. Thin layers of pure Fe of 0.1- and 0.2-mum thickness were evaporated onto both sides of polished 0.6-mm, slices of the giant magnetocaloric material Gd5Si1.5Ge2.5. The slices were stacked for magnetic measurement in the temperature range from 165 to 235 K to assess the MCE. Sample geometries with the iron layers oriented both parallel and perpendicular to the applied field were measured. In the metamagnetic transition temperature range, the Fe layer in the parallel geometry lowers the onset field of the metamagnetic transition by 4240 Oe for the 0.1-mum layer thickness and by 4940 Oe for the 0.2-mum layer thickness from the base value of 8700 Oe at 187 K in the absence of Fe layers. Furthermore, the 0.1-mum layer of Fe oriented perpendicular to the applied field is found to enhance the entropy change, and thus the magnetocaloric effect, by approximately 11% above its base value at 191.5 K; intriguingly, the 0.2-mum Fe layer does not obviously alter the MCE from its base value. (C) 2003 American Institute of Physics.