Size effect of DyF ₃ nanoparticles on Curie temperature

A series of DyF₃ nanoparticles samples were synthesized by a hydrothermal treatment in an autoclave at 140 °C, 160 °C, 200 °C, and 230 °C for 24 h. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and temperature dependence of magnetic susceptibility. It was found that DyF₃ particles possessed an ellipsoidal shape and size varying from 16 to 225 nm. Moroever, the Curie temperature T_C shifts to lower temperatures when the particle size decreases. For the first ime, the critical exponent of the correlation length (ν = 1.51 ± 0.25) and critical size (d₀ = 1.2 ± 0.6 nm) for the dipole ferromagnet DyF₃ has been determined experimentally by the finite-size-scaling theory.