Magnetocaloric effect of LiErP4O12 single crystal exhibiting competing ferromagnetic and anti-ferromagnetic interactions

In this paper, we discuss the magnetic behavior and magnetocaloric effect of lithium erbium tetraphosphate (LiErP₄O₁₂) single crystal in the temperature range 2–85 K under magnetic fields up to 50 kOe. Detailed investigation of the temperature-dependent magnetization M(T) proves an existence of magnetic ordering below T_m, which has been estimated as a minimum in the dM/dT vs. T dependence. Above T_m, LiErP₄O₁₂ possesses paramagnetic behavior and its magnetic susceptibility follows the Curie-Weiss law giving a higher value of the effective magnetic moment of Er³⁺ compared to the theoretical one. This could be due to the Kramers spin degeneracy and the Stark structure of multiplets. Under an applied field H = 50 kOe, the maximum value of the magnetic-entropy change at 2 K reaches about 15 J/kgK, corresponding to a relative-cooling-power value of ∼343 J/kg. Assessments of the magnetic ordering exponent n and N(T, H) data prove LiErP₄O₁₂ exhibiting short-range magnetic order. Due to the absence of magnetic hysteresis and large magnetocaloric response, we believe that LiErP₄O₁₂ could be a promising candidate for magnetic-cooling applications in liquefying hydrogen and ³He isotope.