<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi></mml:math>-type antiferromagnetic order in the Zintl-phase insulator <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>EuZn</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">P</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>
Tanya Berry, Veronica Stewart, Benjamin W. Y. Redemann, Chris Lygouras, Nicodemos Varnava, David Vanderbilt, Tyrel M. McQueen
Abstract
Zintl phases, containing strongly covalently bonded frameworks with separate ionically bonded ions, have emerged as a critical materials family in which to couple magnetism and strong spin-orbit coupling to drive diverse topological phases of matter. Here we report the single-crystal synthesis, magnetic, thermodynamic, transport, and theoretical properties of the Zintl compound ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ that crystallizes in the anti-${\mathrm{La}}_{2}{\mathrm{O}}_{3}$ (${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$) P-$3m1$ structure, containing triangular layers of ${\mathrm{Eu}}^{2+}$ ions. In-plane resistivity measurements reveal insulating behavior with an estimated activation energy of ${E}_{g}=0.11\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$. Specific heat and magnetization measurements indicate antiferromagnetic ordering at ${T}_{N}=23\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Curie-Weiss analysis of in-plane and out of plane magnetic susceptibility from $T=150$ to 300 K yields ${p}_{\mathrm{eff}}=8.61$ for ${\ensuremath{\mu}}_{0}H\ensuremath{\perp}c$ and ${p}_{\mathrm{eff}}=7.74$ for ${\ensuremath{\mu}}_{0}H//c$, close to the expected values for the $4{f}^{7} J=S=7/2 {\mathrm{Eu}}^{2+}$ ion and indicative of weak anisotropy. Below ${T}_{N}$, a significant anisotropy of ${\ensuremath{\chi}}_{\ensuremath{\perp}}/{\ensuremath{\chi}}_{//}\ensuremath{\approx}2.3$ develops, consistent with $A$-type magnetic order as observed in isostructural analogs and as predicted by the density functional theory calculations reported herein. The positive Weiss temperatures of ${\ensuremath{\theta}}_{W}=19.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for ${\ensuremath{\mu}}_{0}H\ensuremath{\perp}c$ and ${\ensuremath{\theta}}_{W}=41.9\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for ${\ensuremath{\mu}}_{0}H//c$ show a similar anisotropy and suggest competing ferromagnetic and antiferromagnetic interactions. Comparing Eu magnetic ordering temperatures across trigonal $\mathrm{Eu}{M}_{2}{X}_{2}$ ($M=$ divalent metal, $X=$ pnictide) shows that ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ exhibits the highest ordering temperature, with variations in ${T}_{N}$ correlating with changes in expected dipolar interaction strengths within and between layers and independent of the magnitude of electrical conductivity. These results provide experimental validation of the crystochemical intuition that the cation ${\mathrm{Eu}}^{2+}$ layers and the anionic ${({M}_{2}{X}_{2})}^{2--}$ framework can be treated as electronically distinct subunits, enabling further predictive materials design.