Magnetism, heat capacity and electronic structure of EuCd${}_2$P${}_2$ in view of its colossal magnetoresistance

Abstract

The mechanism of the peculiar transport properties around the magnetic ordering temperature of semiconducting antiferromagnetic EuCd${}_2$P${}_2$ is not yet understood. With a huge peak in the resistivity observed above the Néel temperature, $T_{\mathrm{N}}=10.6\mathrm{K}$, it exhibits a colossal magnetoresistance effect. Recent reports on observations of ferromagnetic contributions above $T_{\mathrm{N}}$ as well as metallic behavior below this temperature have motivated us to perform a comprehensive characterization of this material, including its resistivity, heat capacity, magnetic properties and electronic structure. Our transport measurements revealed quite different temperature dependence of resistivity with the maximum at $14\mathrm{K}$ instead of previously reported $18\mathrm{K}$. Low-field susceptibility data support the presence of static ferromagnetism above $T_{\mathrm{N}}$ and show a complex behavior of the material at small applied magnetic fields. Namely, signatures of reorientation of magnetic domains are observed up to $T=16\mathrm{K}$. Our magnetization measurements indicate a magnetocrystalline anisotropy which also leads to a preferred alignment of the magnetic clusters above $T_{\mathrm{N}}$. The momentum-resolved photoemission experiments at temperatures from $24\mathrm{K}$ down to $2.5\mathrm{K}$ indicate the permanent presence of a fundamental band gap without change of the electronic structure when going through $T_N$ that is in contradiction with previous results. We performed \textit{ab initio} band structure calculations which are in good agreement with the measured photoemission data when assuming an antiferromagnetic ground state. Calculations for the ferromagnetic phase show a much smaller bandgap, indicating the importance of possible ferromagnetic contributions for the explanation of the colossal magnetoresistance effect in the related EuZn${}_2$P${}_2$.

13 pages, 9 figures