Interband Faraday and Kerr rotation and magnetization ofPb1−xEuxTein the concentration range 0<x⩽1

Faraday and magneto-optical Kerr effect has been used for the investigation of the band alignment as well as of the magnetic properties of epitaxial layers of the ternary alloy system ${\mathrm{Pb}}_{1-x}{\mathrm{Eu}}_x\mathrm{Te}$ $(0\mathrm{}<~x<~1)$ grown on ${\mathrm{BaF}}_2$ substrates. Due to the wide range of transition energies $(0.19\mathrm{}\mathrm{eV}<~E_g<~2.25\mathrm{eV})$ the experiments had to be performed in the spectral range from midinfrared to visible light. Data were collected at temperatures between 1.8 and 250 K and in magnetic fields up to 7 T. Concomitant magnetization measurements $(B=1\mathrm{}\mathrm{T})$ were performed with a superconducting quantum interference device (SQUID) magnetometer and compared with measurements of the x dependence of the Verdet constant. The variation of the fundamental absorption gap with Eu content can be understood in terms of the relative energetic position of PbTe-related band edges and $\mathrm{Eu}4f$ and $5d$ levels: $\Delta E_g/\Delta x=4.48\mathrm{}\mathrm{eV}$ for $x<\mathrm{}0.06;$ $\Delta E_g/\Delta x=2.03\mathrm{}\mathrm{eV}$ for $0.06<x<\mathrm{}\mathrm{0.6.}\mathrm{}$ For $x>\mathrm{}0.8,$ the electronic transitions are identified to be EuTe-like. The most striking feature is a sign reversal of Verdet’s constant around $x=0.15,$ which is attributed to a crossover of Faraday rotation caused by band electrons (holes) and interacting pairs of magnetic ions and a metal-insulator transition. An antiferromagnetic phase transition is observed for $x>\mathrm{}0.8\mathrm{}$ in magneto-optics as well as in SQUID magnetometry.