Optical properties and carrier localization in the layered phosphide EuCd2P2

The temperature dependence of the complex optical properties of the layered phosphide material EuCd2P2 have been measured over a wide frequency range above and below TN similar or equal to 11.5 K for light polarized in the a -b planes. At room temperature, the optical conductivity is well described by a weak free-carrier component with a Drude plasma frequency of similar or equal to 1100 cm -1 and a scattering rate of 1/rD similar or equal to 700 cm -1, with the onset of interband absorptions above similar or equal to 2000 cm -1. Two infrared-active Eu modes are observed at similar or equal to 89 and 239 cm -1. As the temperature is reduced the scattering rate decreases and the low-frequency conductivity increases slightly; however, below similar or equal to 50 K the conductivity decreases until at the resistivity maximum at similar or equal to 18 K (just below 2TN) the spectral weight associated with free carriers is transferred to a localized excitation at similar or equal to 500 cm -1. Below TN, metallic behavior is recovered. Interestingly, the Eu modes are largely unaffected by these changes, with only the position of the high-frequency mode showing any signs of anomalous behavior. While several scenarios are considered, the prevailing view is that the resistivity maximum and subsequent carrier localization is due to the formation of ferromagnetic domains below similar or equal to 2T(N) that result in spin-polarized clusters due to spin-carrier coupling.