Giant magnetocaloric effect in antiferromagnetic borocarbide superconductor RNi₂B₂C (R Dy, Ho, and Er) compounds

The magnetocaloric effect (MCE) in antiferromagnetic borocarbide superconductor RNi₂B₂C (R = Dy, Ho, and Er) compounds have been investigated by measuring the temperature and field dependences of heat capacity. An inverse MCE was observed, which is attributed to the nature of the antiferromagnetic state under low magnetic field and at low temperatures for the present RNi₂B₂C compounds. A normal giant/large MCE was observed under higher magnetic field change, which is related to a field-induced first-order metamagnetic transition from antiferromagnetic to ferromagnetic state. For a field change of 5 T, the maximum values of magnetic entropy change (- δS_M^max) reach 17.6, 17.7, and 9.8 J kg ^-1 K^-1 for R = Dy, Ho, and Er, respectively. The corresponding values of maximum adiabatic temperature changes (δT _ad^max) are 9.7, 11, and 4.6 K. The present results indicated the antiferromagnetic borocarbide superconductor RNi₂B ₂C compounds could be promising candidates for low temperature magnetic refrigeration.