Magnetocaloric Behavior in Ternary Europium Indides EuT₅In: Probing the Design Capability of First-Principles-Based Methods on the Multifaceted Magnetic Materials

Abstract

The most favorable structures and the types of magnetic ordering predicted from first-principles-based methods in a family of closely related transition-metal-rich indides EuT<sub>5</sub>In (T = Cu, Ag, Au) are gauged against relevant experiments. The EuT5In compounds adopt a different structure for each different coinage metal—EuCu<sub>5</sub>In (<i>hR</i>42; <i>R</i>$\\overline{3}$m, <i>a</i> = 5.0933(7), <i>c</i> = 30.557(6) Å), EuAg<sub>5</sub>In (<i>oP</i>28; <i>Pnma</i>, <i>a</i> = 9.121(2), <i>b</i> = 5.645(1), <i>c</i> = 11.437(3) Å), and EuAu<sub>5</sub>In (<i>tI</i>14; <i>I</i>4/<i>mmm</i>, <i>a</i> = 7.1740(3), <i>c</i> = 5.4425(3) Å)—and crystallize with the Sr<sub>5</sub>Al<sub>9</sub>, CeCu<sub>6</sub>, and YbMo<sub>2</sub>Al<sub>4</sub> structure types, respectively. EuCu<sub>5</sub>In and EuAg<sub>5</sub>In order antiferromagnetically at T<sub>N</sub> = 12 and 6 K, respectively, whereas EuAu<sub>5</sub>In is ferromagnetic below T<sub>C</sub> = 13 K. EuCu<sub>5</sub>In exhibits complex magnetism: after the initial drop at T<sub>N</sub>, the magnetization rises again below 8 K, and a weak metamagnetic-like transition occurs at 2 K in μ<sub>0</sub>H = 1.8 T. The electronic heat capacity of EuCu<sub>5</sub>In, γ = ~400 mJ/(mol K<sup>2</sup>), points to strong electronic correlations. Spin-polarized densities of states suggest that the magnetic interactions in the three materials studied are supported via mixing 4<i>f</i> and 5<i>d</i> states of Eu. As a result, a chemical bonding analysis based on the Crystal Orbital Hamilton populations reveals the tendency to maximize overall bonding as a driving force to adopt a particular type of crystal structure.