Investigation of multiferroic order in M3TeO6 (M=Co, Mn, Ni) by second harmonic generation

Orthotellurates with the formula M3TeO6 are structurally well characterized and can be divided into six different structure types. According to this, these materials show a wide range of magnetic phases. Recently it was suggested, that in some of the orthotellurates multiferroic order is possible. Among this are: Co3TeO6 (space group C2/c) and Mn3TeO6 (R anti 3) with two magnetic phase transitions as well as Ni3TeO6 (R3) with one magnetic phase transition. However, a direct proof of ferroelectricity has not been reported so far. Here, we investigate the multiferroic order by second harmonic generation (SHG) spectroscopy. For Co3TeO6 we measured a intense SHG contribution in the low temperature phase below 18 K, which is a strong evidence for multiferroic order. This interpretation is supported by the observation of complex domain patterns using SHG imaging techniques.