Magnetocaloric effect in NiMnGa particles produced by spark erosion
The magnetic entropy change of tetragonal and orthorhombic NiMnGa fine particles made by spark erosion was investigated in this paper. It was found that the structure and crystalline phase transformation temperatures can be strongly affected by the compositions of the particles, while Curie temperature is less sensitive to the compositions. Due to the possible distribution of the particle size and compositions in these particles, the magnetic entropy changes observed are much broader and smaller than those of bulk NiMnGa alloys. The maximum absolute value of entropy change ΔS=2JKg−1K−1 was observed for tetragonal structure NiMnGa particles at 95°C in a field of 2T.
Abstract Many human operations have created a large population of small orbital debris in near Earth environment. The threat they represent for satellites is a major factor for the preparation of future space missions. Several experiments devoted to the study of this environment, as well as various materials exposed to space, have been retrieved in the past few years. The analysis of the results shows some differences with previous modeling. Comparison with data from LDEF and from EURECA give some insight in the long term evolution of particle size distribution. Chemical identification of particle remnants inside craters is difficult but provides valuable information on the origin of the impactors. Permanent monitoring of environment is obviously needed, especially for the type of orbits where data are presently scarce ie. heliosynchronous and geostationary orbits.