Investigating the magnetic and magnetocaloric behaviors of LiSm(PO3)4

Abstract

We report a detailed study on the magnetic behaviors and magnetocaloric (MC) effect of a single crystal of lithium samarium tetraphosphate, LiSm(PO₃)₄. The analyses of temperature-dependent magnetization data have revealed magnetic ordering established with decreasing temperature below T_p, where T_p is the minimum of a dM/dT vs. T curve and varies as a linear function of the applied field H. The Curie temperature has been extrapolated from T_p(H) data, as H → 0, to be about 0.51 K. The establishment of magnetic-ordering causes a substantial change in the heat capacity C_p. Above T_p, the crystal exhibits paramagnetic behavior. Using the Curie–Weiss (CW) law and Arrott plots, we have found the crystal to have a CW temperature θ_CW ≈ −36 K, and short-range magnetic order associated with a coexistence of antiferromagnetic and ferromagnetic interactions ascribed to the couplings of magnetic dipoles and octupoles at the Γ₇ and Γ₈ states. An assessment of the MC effect has shown increases in value of the absolute magnetic-entropy change (|ΔS_m|) and adiabatic-temperature change (ΔT_ad) when lowering the temperature to 2 K, and increasing the magnetic-field H magnitude. Around 2 K, the maximum value of |ΔS_m| is about 3.6 J kg⁻¹ K⁻¹ for the field H = 50 kOe, and ΔT_ad is about 5.8 K for H = 20 kOe, with the relative cooling power (RCP) of ∼82.5 J kg⁻¹. In spite of a low MC effect in comparison to Li(Gd,Tb,Ho)(PO₃)₄, the absence of magnetic hysteresis reflects that LiSm(PO₃)₄ is also a candidate for low-temperature MC applications below 25 K.