Ferromagnetism in partially oxidized CuCl

A search for superconductivity in systems of CuCl/Si and CuCl2/Si leads to the observation of ferromagnetism with a Tc of 18 K in powder samples. The magnetism emerges when pure CuCl is exposed to humid air, while the observed magnetic moment depends on the exposure level. We used magnetic field modulated microwave spectroscopy, as well as SQUID magnetometry, to identify magnetic phase transitions as a function of temperature. Crystallographic phase information of partially oxidized CuCl specimens is obtained via x-ray diffraction and Rietveld refinement. Transition temperature and moment are found to be unmatched with transitions in CuCl based compounds reported to date.