MAGNETIC-FIELD-INDUCED FERROELECTRICITY IN COPPER-DOPED CDI2 SINGLE-CRYSTALS

We have discovered a new type of ferroelectricity in highly anisotropi c CdI2 layered crystals doped with copper. A spontaneous electric pola rization is created in result of interaction between long-range interl ayer polar acoustical vibrations and magnetically oriented copper ions . The phenomenon is strongly enhanced after applying external magnetic held at liquid helium temperatures. The strongest effect has been obs erved in the case of magnetic field direction perpendicular to the lay ers. Optical measurements were carried out using a second harmonic gen eration method.