In electrically polar solids optomechanical effects result from the combination of two main processes, electric field-induced strain and photon-induced voltages. Whereas the former depends on the electrostrictive ability of the sample to convert elec
tric energy into mechanical energy, the latter is caused by the capacity of photons with appropriate energy to generate charges and, therefore, can depend on wavelength.We report here on mechanical deformation of BiFeO3 and its response time to discrete wavelengths of incident light ranging from 365 to 940 nm. The mechanical response of BiFeO3 is found to have two maxima in near-UV and green spectral wavelength regions.
We demonstrate that ethylammonium copper chloride, (C2H5NH3)2CuCl4, a member of the hybrid perovskite family is an electrically polar and magnetic compound with dielectric anomaly around the Curie point (247 K). We have found large spontaneous electr
ic polarization below this point accompanied with a color change in the sample. The system is also ferroelectric, with large remnant polarization (37{mu}C/cm2) that is comparable to classical ferroelectric compounds. The results are ascribed to hydrogen-bond ordering of the organic chains. The coexistence of ferroelectricity and dominant ferromagnetic interactions allows to relate the sample to a rare group of magnetic multiferroic compounds. In such hybrid perovskites the underlying hydrogen bonding of easily tunable organic building blocks in combination with the 3d transition-metal layers offers an emerging pathway to engineer multifuctional multiferroics.
