Spin-1/2 $XXZ$ Heisenberg cupolae: magnetization process and related enhanced magnetocaloric effect

Abstract

The magnetization process and adiabatic demagnetization of antiferromagnetic spin-1/2 XXZ Heisenberg clusters with the shape of Johnson's solids (triangular cupola, square cupola and pentagonal cupola) are examined using the exact numerical diagonalization depending on a relative strength of the exchange anisotropy. It is demonstrated that XXZ Heisenberg cupolae display at least one more magnetization plateau, which is totally absent in Ising cupolae. The novel magnetization plateaux extend over a wider range of magnetic field with increasing of a quantum part of the XXZ exchange interaction at the expense of the original plateaux present in the Ising limiting case. It is shown that XXZ Heisenberg triangular and pentagonal cupola exhibits in the proximity of all magnetization jumps an enhanced magnetocaloric effect in a vicinity to zero magnetic field, making these magnetic systems a promising refrigerant for cooling down to absolute temperature.