Experimental and theoretical investigation of magnetoelectric (ME) coupling in aligned multiferroic Janus fibers using second harmonic generation (SHG) polarimetry at different magnetic field orientations

Due to the absence of substrate clamping and high surface-to-volume ratio, heterostructure multiferroic fibers have been shown to support large ME coupling compared to their thin film counterparts. Here, the ME coupling in an ensemble of multiferroic Janus fibers consisting of ferrimagnetic cobalt ferrite (CFO) and ferroelectric barium titanate (BTO) is investigated using second harmonic generation (SHG) technique under different magnetic field orientations. We fit the experimental data by incorporating the known second order susceptibility tensor elements for bulk BTO and directly calculate the second order polarization. Our fits provide key information about the relative contribution of different ferroelectric BTO domains to the SHG polarization and help construct a 3D picture of how the domains redistribute upon changing the magnetic field orientation. We also find that the fibers in the ensemble behave similarly despite their inhomogeneity. We attempt to qualitatively relate the changes in the BTO to the expected changes in the CFO to gain insights into how the strain mediates the magnetoelectric (ME) coupling between the two constituents of multiferroic Janus fibers.