Colossal magnetoresistance in EuZn₂P₂ and its electronic and magnetic structure

We investigate single crystals of the trigonal antiferromagnet EuZn2P2 (P (3) over bar 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 (DFT + U). We find that the electrical resistivity of EuZn2P2 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 0 1/2), corresponding to an A-type antiferromagnetic order, below T-N = 23.7 K. We find that the moments are canted out of the a-a plane by an angle of about 40 degrees +/- 10 degrees and aligned along the [100] direction in the a-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 approximate to 150 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 K allows us to resolve the main phonon bands and intraband and interband transitions, and estimate indirect and direct band gaps of E-i(opt) = 0.09 and E-d(opt) = 0.33 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-N. The comparison of the theoretical and experimental data shows a weak intermixing of the Eu 4f states close to the Gamma point with the bands formed by the phosphorous 3p orbitals leading to an induction of a small magnetic moment at the P sites.