An Effective Route to Control the Magnetic-Phase Transition and Magnetocaloric Effect of La_0.7Ca_0.3MnO₃ Nanoparticles

摘要

This paper points out that the magnetic-phase transition and magnetocaloric effect of LaCaMnO (LCMO) can be easily controlled by using the mechanical milling method. Changing the milling time from 5 to 30 min, we have obtained LCMO nanoparticles (NPs) with average crystallite sizes (d, determined by the Williamson-Hall method) ranging from 100 to 45 nm. The magnetic studies (based on a superconducting quantum interference device) and simple analyses (based on Banerjee's criteria) prove the magnetic-phase transformation from the first-order to the second-order, which takes place at a threshold value of d located in the range 60-70 nm. Compared with the as-prepared LCMO sample (a first-order magnetic phase transition), though the d decrease reduces the values of the T, magnetization, magnetic-entropy change, and refrigerant capacity, but the width of the magnetic phase transition is increased remarkably. This widens the working range of LCMO NPs in magnetic refrigeration applications. We believe that the presence of surface-related effects, lattice strain, and distortions leads to Mn-Mn ferromagnetic interactions in LCMO NPs weaker than that in the as-prepared sample.