Phase Transition in Mixed Spin Ising Nanoparticles

The phase transitions of two mixed-spin (1/2,1) Ising nanoparticles with n = 4.0 and n = 6.0 are investigated by using the effective-field theory with correlations (EFT). The spin-1 atom with a single-ion anisotropy is decorated at the center of regular n-polygon (or nanoparticle with a value of n) and the spin-1/2 n atoms are put at the perimeter n sites. The phase transition in the nanoparticle with n = 6.0 is rather different from that in the nanoparticle with n = 4.0. It is shown that the number of n plays just like the coordination number z in the bulk mixed-spin Ising systems: the hexagonal nanoparticle with n = 6.0 has exhibited the first-order transition and the tricritical behavior, although the tetragonal nanoparticle with n = 3.0 did not show such behaviors, depending on the values of exchange interactions.