Large magntocaloric effect and 3D Ising critical behaviour in Gd$_2$Cu$_2$In

TL;DR

This study investigates the magnetic and magnetocaloric properties of Gd$_2$Cu$_2$In near its ferromagnetic transition at 94 K, revealing significant entropy change, critical behavior consistent with 3D Ising and mean field models, and confirming bulk magnetic ordering.

Contribution

The paper provides detailed critical exponents and magnetocaloric measurements for Gd$_2$Cu$_2$In, highlighting its unique universal class and 3D Ising critical behavior.

Findings

Maximum entropy change of 13.8 J/kg.K at 7 T

Critical exponents suggest 3D Ising and mean field behavior

Confirmation of bulk magnetic ordering at 94 K

Abstract

The ternary intermetallic compound Gd$_2$Cu$_2$In crystallizes in Mo$_2$Fe$_2$B type structure with the space group $P4/mbm$ and we study critical behaviour and magnetocaloric effect near the ferromagnetic transition ($T_C$ $\approx$ 94 K) using the magnetic and heat capacity measurements. The maximum entropy change ($\Delta S_m$) and adiabatic temperature change ($\Delta T_{ad}$) for the field value of 7 T were observed to be 13.8 J/kg.K and 6.5 K respectively. We have employed modified Arrott plot (MAP), Kouvel-Fisher (KF) procedures to estimate the critical exponents near the FM-PM phase transition. Critical exponents $\beta$ = 0.312(2), $\gamma$ = 1.080(5) are self-consistently estimated from the non-linear fitting. The $\beta$ value is close to the three dimensional (3D) Ising model where as $\gamma$ and $\delta$ values are close to mean field model. The estimated critical exponents for Gd$_2$Cu$_2$In suggest that the system may belong to different universal class. All the three critical exponent obey Widom scale and collapse the scaled magnetic isotherms into two distinct branches below and above $T_C$ in accordance with single scaling equation. Specific heat measurements show a $\lambda$ type peak near 94 K confirming the bulk magnetic ordering. The data near $T_C$ was fitted using the non-linear function $C_{P} = B + C\epsilon + A^{\pm}|\epsilon|^{-\alpha}(1 + E^{\pm} |\epsilon|^{0.5})$ between -0.025$<\epsilon<$0.025 which yielded the fourth critical exponent $\alpha$ value to be 0.11 (3). The value indicates possible 3D-Ising behavior where Gd$^{3+}$ moments arranged uniaxially along long tetragonel axis 'c' as reported in literature.