Magnetic polaron formation in EuZn${}_2$P${}_2$

Abstract

Colossal magnetoresistance (CMR) has been observed across many Eu${}^{2+}$-based materials; however, its origin is not completely understood. Here we investigate the antiferromagnetic insulator EuZn${}_2$P${}_2$ through single crystal x-ray diffraction, transmission electron microscopy, electrical transport, magnetization, dilatometry, and electron spin resonance measurements complemented by density functional theory calculations. Our electrical resistivity data reveal a large negative magnetoresistance, $MR=[R(H)-R(0)]/R(0)$, that reaches $MR=-99.7\%$ at 9~T near the antiferromagnetic ordering temperature $T_N=23\text{K}$. Dilatometry measurements show an accompanying field-induced lattice strain. Additionally, Eu${}^{2+}$ electron spin resonance reveals a strong ferromagnetic exchange interaction between Eu${}^{2+}$ and conduction electrons. Our experimental results in EuZn${}_2$P${}_2$ are consistent with a magnetic polaron scenario and suggest magnetic polaron formation as a prevailing explanation of CMR in Eu${}^{2+}$-based compounds.