Colossal magnetoresistance in <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> and its electronic and magnetic structure

Abstract

We investigate single crystals of the trigonal antiferromagnet ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ ($P\overline{3}m1$) by means of electrical transport, magnetization measurements, x-ray magnetic scattering, optical reflectivity, angle-resolved photoemission spectroscopy (ARPES), and ab initio band structure calculations ($\mathrm{DFT}+U$). We find that the electrical resistivity of ${\mathrm{EuZn}}_{2}{\mathrm{P}}_{2}$ increases strongly upon cooling and can be suppressed in magnetic fields by several orders of magnitude (colossal magnetoresistance effect). Resonant magnetic scattering reveals a magnetic ordering vector of $q=(0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}\frac{1}{2})$, corresponding to an $A$-type antiferromagnetic order, below ${T}_{\mathrm{N}}=23.7\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. We find that the moments are canted out of the $a\text{\ensuremath{-}}a$ plane by an angle of about ${40}^{\ensuremath{\circ}}\ifmmode\pm\else\textpm\fi{}{10}^{\ensuremath{\circ}}$ and aligned along the [100] direction in the $a\text{\ensuremath{-}}a$ plane. We observe nearly isotropic magnetization behavior for low fields and low temperatures which is consistent with the magnetic scattering results. The magnetization measurements show a deviation from the Curie-Weiss behavior below $\ensuremath{\approx}150\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, the temperature below which also the field dependence of the material's resistivity starts to increase. An analysis of the infrared reflectivity spectrum at $T=295\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ allows us to resolve the main phonon bands and intraband and interband transitions, and estimate indirect and direct band gaps of ${E}_{i}^{\mathrm{opt}}=0.09$ and ${E}_{d}^{\mathrm{opt}}=0.33\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$, respectively, which are in good agreement with the theoretically predicted ones. The experimental band structure obtained by ARPES is nearly $T$ independent above and below ${T}_{\mathrm{N}}$. The comparison of the theoretical and experimental data shows a weak intermixing of the Eu $4f$ states close to the $\mathrm{\ensuremath{\Gamma}}$ point with the bands formed by the phosphorous $3p$ orbitals leading to an induction of a small magnetic moment at the P sites.

Topics & Concepts