Large magnetocaloric effect in Li <i>Ln</i> P ₄ O ₁₂ ( <i>Ln</i> = Gd, Tb, Dy) single crystals

Abstract

Abstract We have studied the magnetic and magnetocaloric (MC) properties of lithium lanthanide tetraphosphates Li Ln P 4 O 12 ( 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 (| <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mi>S</mml:mi> <mml:mi>m</mml:mi> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> |) 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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi>a</mml:mi> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mo form="prefix" movablelimits="true">max</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ) 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 | <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>Δ</mml:mi> <mml:msubsup> <mml:mi>S</mml:mi> <mml:mi>m</mml:mi> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> |, RC and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mrow> <mml:mi>a</mml:mi> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:mo form="prefix" movablelimits="true">max</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> , and the absence of magnetic hysteresis, Li Ln P 4 O 12 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 Li Ln P 4 O 12 SCs are related to the ground-state nature and spin-orbit interaction of Ln 3+ ions.

Topics & Concepts