Large magnetocaloric effect in LiLnP4O12 (Ln = Gd, Tb, Dy) single crystals

Abstract

Abstract We have studied the magnetic and magnetocaloric (MC) properties of lithium lanthanide tetraphosphates LiLnP4O12 (Ln = Gd, Tb, Dy) single crystals (SCs) upon the magnetization (M) and heat-capacity (Cp) measurements. Detailed investigations in the temperature range T = 2–300 K indicate that all SCs exhibit paramagnetic (PM) character with effective PM moments close to those expected for free Ln 3+ ions. The magnetic contribution to Cp takes place strongly at temperatures below 20 K that enhances the values of the parameters characteristic for the MC effect. Under an applied field H = 50 kOe, the values of the maximum magnetic entropy change (| Δ S m max |) at 2 K are about 27.6, 15.9 and 11.7 J kg−1 K−1 for Ln = Gd, Tb and Dy, respectively, corresponding to refrigerant capacity (RC) of 133 ∼ 254 J kg−1. Among the studied SCs, the maximum adiabatic temperature change ( Δ T a d max ) obtained for the system Ln = Gd at a field change H = 20 kOe is about 13 K, which can be achieved by using a permanent magnet. With the large values of | Δ S m max |, RC and Δ T a d max , and the absence of magnetic hysteresis, LiLnP4O12 are considered as alternatively potential candidates for adiabatic magnetic refrigeration applications at sub-helium temperatures. It is believed that the different magnetic and MC properties among the LiLnP4O12 SCs are related to the ground-state nature and spin-orbit interaction of Ln 3+ ions.