Influence of the crystalline electrical field on the magnetocaloric effect ofDyAl2,ErAl2,andDyNi2

Abstract

Calculations of the magnetic entropy change $\ensuremath{\Delta}{S}_{\mathrm{mag}}$ and the magnetocaloric effect (i.e., the adiabatic temperature change) $\ensuremath{\Delta}{T}_{\mathrm{ad}}$ in ${\mathrm{DyAl}}_{2},{\mathrm{ErAl}}_{2},$ and ${\mathrm{DyNi}}_{2}$ using a Hamiltonian that takes into account the effects of crystalline electrical field and exchange interaction have been carried out. Good agreement between the theory and the experiment was obtained using the crystal-field parameters from inelastic neutron scattering for ${\mathrm{DyAl}}_{2}$ and ${\mathrm{ErAl}}_{2}.$ The crystal-field parameters for ${\mathrm{DyNi}}_{2},$ which were reported from magnetization measurements, did not give good agreement between the theory and the experiment. Using the experimental $\ensuremath{\Delta}{S}_{\mathrm{mag}}$ versus T, and ${C}_{\mathrm{mag}}$ versus T (where ${C}_{\mathrm{mag}}$ is the magnetic heat capacity) we made an estimate of the crystal-field parameters for ${\mathrm{DyNi}}_{2},$ which yield a satisfactory agreement between the theory and the experiment with regard to $\ensuremath{\Delta}{S}_{\mathrm{mag}}$ and $\ensuremath{\Delta}{T}_{\mathrm{ad}}.$ The appearance of a hump in the theoretical $\ensuremath{\Delta}{S}_{\mathrm{mag}}(T)$ below the Curie temperature is discussed.