Direct and inverse magnetocaloric effects in the antiferromagnetic rare earth (RE) rich RE6Ni2.25Al0.75 (RE = Dy, Ho and Er) compounds

The magnetic refrigeration (MR) by utilizing the magnetocaloric effect (MCE) of magnetic solids has been considered a promising, environmentally benign, energy-efficient cooling technology. However, the lack of promising magnetic substances has slowed the development of its active application. To identify suitable candidate materials, we herein identified the structural and magnetic properties together with the MCE and magnetocaloric performances of rare earth (RE) rich RE6Ni2.25Al0.75 (RE = Dy, Ho and Er) compounds. All the RE6Ni2.25Al0.75 compounds are confirmed to crystallized in orthogonal Ho6Co2Ga-type structure and underwent paramagnetic to antiferromagnetic magnetic transitions. Moreover, large direct (conventional) and inverse MCEs have been observed in all the RE6Ni2.25Al0.75 compounds. The values of peak magnetic entropy changes, temperature-averaged magnetic entropy changes with 5 K-lift and relative cooling powers under magnetic field change of 0–7 T are evaluated to be − 4.44 J/kg-K, − 4.38 J/kg-K and 230.6 J/kg for Dy6Ni2.25Al0.75, to be − 12.68 J/kg-K, − 12.26 J/kg-K and 378.2 J/kg for Ho6Ni2.25Al0.75, and to be − 17.52 J/kg-K, − 17.33 J/kg-K and 465.7 J/kg for Er6Ni2.25Al0.75, respectively.