Low-temperature anomalies and ferromagnetism of EuB6

Measurements of the specific heat C-p(T) of single-crystalline EuB6 reveal that the magnetically ordered ground state of this compound is reached via two consecutive phase transitions with onsets at 16 and 14 K, respectively. These transitions provoke a substantial change in the IR spectral range of the electronic excitation spectrum as evidenced by measurements of the optical reflectivity over a wide spectral range and at temperatures between 6 K and room temperature. The data analysis suggests that the magnetic ordering of EuB6 inflicts a highly unusual alteration of its electronic excitation spectrum.