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Magnetic susceptibility, phonons and dielectric constant of single crystalline BiFeO3

The magnetic susceptibility between 1.5 and 800 K, the infrared reflectivity at room temperature and the temperature dependence of the dielectric constant at mm-wavelengths are reported for single crystalline BiFeO3. A well developed anomaly in the magnetic susceptibility signals the onset of antiferromagnetic order close to 640 K. Beside this anomaly, no further indications of phase or spin-glass transitions are found in the susceptibility down to the lowest temperatures. From infrared reflectivity we were able to identify all 9 phonon modes which are expected to be infrared active within the ab plane of the crystal. The temperature dependence of the dielectric constant was measured contact free in the 100 GHz range yielding e' = 54 at room temperature. The loss is substantial and strongly frequency dependent indicating the predominance of hopping conductivity.