Structural disorder effects on the magnetic entropy change of DyCo2 intermetallic

Abstract

Magnetocaloric properties of the intermetallic DyCo2 compound (in the form of reduced size particles) and its correlations with the itinerant electron metamagnetism (IEM) phenomenon and structural disorders are investigated and discussed. Micrometric-sized particles were prepared by a mechanical milling technique for two low milling times (4 and 8 h) and characterized by means of X-ray diffraction, scanning and high-resolution transmission electron microscopy as well as magnetic measurements as a function of an applied external magnetic field and temperature. The results show that the particles have irregular-shaped and amorphous "edges/ledges" with embedded randomly oriented DyCo2 nanocrystallites. The average particle size practically does not change with increasing milling time, whereas the average crystallite size is slightly diminished. In contrast, microstrain values that indicate lattice deformation degree were rather increased after the milling processes. Structural disorders and surface effects, features resulting from mechanical impact, disturb the Dy-Co sublattice coupling and weaken the IEM mechanism responsible for the high magnetocaloric effect found for the DyCo2 bulk sample. For the milled samples, it was observed reductions in the peak intensity of the magnetic entropy change (-Delta S-M) and substantial broadenings of the distribution profiles which have contributed to an increase of the working temperature range of the investigated magnetocaloric material.