Physical properties of potassium erbium double tungstate KEr(WO4)2

The paper presents the results of complex investigations of the potassium-erbium double tungstate. The following properties have been measured: specific heat, specific heat in magnetic field, thermal expansion, thermal expansion in magnetic field, magnetization and X-ray structural data, reflectance and optical absorption spectra. The experiments were performed in the broad temperature range from 0.4 K to 300 K, spectral range from 4000 cm-1 to 40000 cm-1 and magnetic field up to 10T. The magnetic phase transition was found at temperature T=0.84K. In thermal expansion experiment the strong anomaly was found at T=7.6 K in magnetic field 10T. The KEr(WO4)2 belongs to the optical class of biaxial and pleochroic (trichroic) crystals. Using spectroscopy methods, the orientation of optical axes and refractive indices have been found. The main optical absorption spectra have been measured. The temperature dependence of optical absorption was determined.