Alexandre Magnus G. Carvalho

Ambient pressure colossal magnetocaloric effect in Mn1−xCuxAs compounds

Magnetic refrigeration is a good alternative to gas compression technology due to higher efficiency and environmental concerns. Magnetocaloric materials must exhibit large adiabatic temperature variations and a large entropic effect. MnAs shows the colossal magnetocaloric effect under high pressures or with Fe doping. In this work the authors introduce a class of materials—Mn1−xCuxAs—revealing a peak colossal effect of −175J∕(Kkg) for a 5T field variation at 318K and ambient pressure.

Giant magnetocaloric effect in Gd5(Si2Ge2) alloy with low purity Gd

Gd5(Ge1-xSix), x < 4 based alloys are potential candidates for magnetic refrigeration in the range ~20 - ~290 K. However, one of the greatest obstacles for the use of that technology in large scale is the utilization of high pure Gd metal (99.99 wt. (%)) to produce the GdGeSi alloys, since the impurity elements decrease the intensity of the magnetocaloric effect (EMC)1. In this work, we prove that annealing of the Gd5Ge2Si2 can promote remarkable values for the EMC in comparison to those obtained for the alloy with high pure Gd. Also, the as cast alloy and the annealed alloy are not monophasic, but have at least two crystalline phases in their microstructure. Results for X-ray analysis, optical and electronic microscopy and magnetization measurements are reported.

Study of structural and magnetic properties presented by Tb1-xPrxNi2 compounds

On the search for better cores for cryogenic magnetic refrigeration, magnetic and structural properties, such as synchrotron x ray diffraction and magnetization of Tb1-xPrxNi2 were studied. The results show the linear behavior of the lattice parameter and the Curie temperature.