Magnetic performances and cryogenic magnetocaloric effects of NaREGeO₄ (RE=Dy, Ho, Tb and Er) compounds

Adiabatic demagnetization refrigeration (ADR) has been regarded as an alternative to helium-3-based refrigeration technology and received much attention. In this paper, NaREGeO₄ (RE = Dy, Ho, Tb and Er) series compounds are prepared using the solid-state reactions, and their crystal structures, magnetic properties, and magnetocaloric effects (MCE) are studied. According to Cuire Weiss fitting, four compounds all exhibit antiferromagnetic ground states. The maximum magnetic entropy changes (-ΔS_M) are calculated to be 13.76 J kg⁻¹ K⁻¹ (Dy: 4.5 K), 15.18 J kg⁻¹ K⁻¹ (Ho: 4.5 K) and 16.05 J kg⁻¹ K⁻¹ (Er: 3 K), which are close to their corresponding theoretical magnetic entropy evaluated by Ising spin model. For NaTbGeO₄, it possesses smallest -ΔS_M value of 5.91 J kg⁻¹ K⁻¹ due to the existence of strong short-range antiferromagnetic order. These performances suggest that NaREGeO₄ compounds are promising candidates for low-temperature magnetic refrigeration applications.