Magnetism and cryogenic magnetocaloric effect of triangular-lattice LnOF (Ln = Gd, Dy, Ho, and Er) compounds

Frustrated lanthanide oxides with dense magnetic lattice and suppressed ordering temperature have potential applications in cryogenic magnetic refrigeration. Herein, the crystal structure, magnetic properties, magnetic phase transition (MPT) together with magnetocaloric effect (MCE) of LnOF (Ln = Gd, Dy, Ho, and Er) compounds were investigated. Crystallographic study shows that these compounds crystallize in the centrosymmetric space group R3¯m with an ideal triangular lattice. No long-range magnetic ordering is observed above 2 K for LnOF (Ln = Gd, Ho, and Er). However, DyOF compound undergoes an MPT from paramagnetic (PM) to antiferromagnetic (AFM) at the Néel temperature (T_N ≈ 4 K). Considerable reversible MCE is observed in these triangular-lattice compounds. Under the magnetic field change (μ₀ΔH) of 0–2 T, the maximum values of magnetic entropy change (-ΔS_M^max) of them are 6.1, 9.4, 12.7, and 14.1 J/(kg·K), respectively. Interestingly, the value of ErOF with Ising-like spin is 2.3 times that of GdOF, which provides an approach for exploring magnetic refrigerants with excellent low-field cryogenic magnetocaloric effect.