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

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.

Large Magnetocaloric Effect in Li3K9Gd3(BO3)7 Crystal Featuring Sandwich-Like Three-Dimensional Framework

“…At the lowest possible temperature, the ideal MC material should have a degenerate paramagnetic state, that is, there is no coupling between the magnetic moments. The coupling between the magnetic moments is normally correlated to the distance between RE 3+ ions, which leads to magnetic ordering at the Neel or Curie temperature . For Li 3 K 9 Gd 3 (BO 3 ) 7 , the Gd···Gd separations within the zigzag [Gd–O] ∞ chains are 4.8767 Å for Gd(2)···Gd(2) and 5.2875 Å for Gd(2)···Gd(1), respectively.…”

“…The coupling between the magnetic moments is normally correlated to the distance between RE 3+ ions, which leads to magnetic ordering at the Neel or Curie temperature. 8 For Li GdVO 4 (3.93 Å), 39 and GdPO 4 (4.03 Å), 40 which is obviously beneficial to generating a large magnetocaloric effect. Magnetic properties.…”

“…The magnetic-cooling (MC) based on the magnetocaloric effect (MCE) is expected to replace the conventional vapor cycle refrigeration owing to its environmental safety benefits, high thermal cycling efficiency, and low power consumption. − In particular, in the field of space science and low-temperature physics, the adiabatic demagnetization refrigerator (ADR) making use of MC materials has been believed as an ideal technique to achieve a sub-Kelvin range. − The RE-rich compounds with highly localized f orbitals are good candidates for MC materials owing to their weak magnetic interactions. Especially for Gd 3+ ions, the half-filled 4f orbital with a large spin state of S = 7/2 makes a great contribution to the magnetic entropy change (−Δ S m ). , Consequently, the Gd-based MC materials have been attracting extensive attention.…”

“…Recently, great efforts have been dedicated to developing new Gd-based MC materials with light organic carboxylate ligands (such as [HCOO] − , [CH 3 COO] − , and [C 2 O 4 ] 2– ) and short inorganic ligands (such as [PO 4 ] 3– , [OH] − , [CO 3 ] 2– , and [SO 4 ] 2– ) because the small anion ligands and high Gd 3+ ions concentrations are profitable for inducing the large −Δ S m , that is, the high Gd 3+ ions/ligands ratio leads to a high mass density and generates a greater volumetric MCE, so long as the magnetic interaction between Gd 3+ ions does not prevent from generating the desired MCE. For instance, Gd­(HCOO) 3 , [Gd­(PDOA)­(NO 3 )­(H 2 O) 3 ] n , Gd­(C 2 O 4 ) 0.5 (CO 3 )­(H 2 O), Gd­(OH)­CO 3 , Gd 2 Cu­(SO 4 ) 2 (OH) 4 , and LiGdP 4 O 12 present some heightened MCE properties. Unfortunately, they undergo poor thermal stability or physicochemistry, which hinder their practical application for ADR .…”

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

“…31,32 Together with the 3D framework, a large nearest Re-Re distance (∼5.6 Å 31,33 ) is thought to obstruct exchange interactions between Re ions, leading to a large MC effect of LiRe(PO 3 ) 4 at low temperatures. Investigating LiRe(PO 3 ) 4 materials with Re = Gd, Tb, Dy and Pr, Petrov et al 27,32 found their jDS m j and DT ad values at 2 K are about 9.8-27.6 J kg −1 K −1 for the eld H = 50 kOe and 3-13 K for H = 20 kOe, respectively.…”