Characterization Of Ferroelectric Domain States In Multiferroics By Optical Second Harmonic Generation

In the generation of data,we have higher requirements on the speed,power consumption and security of data processing and storage.However,the mechanism of reading or writing in traditional hard disk as well as the storage modes are increasingly unable to meet people's needs.In order to solve the problems of decreasing field-building time and Joule heat of the current in the traditional read-write magnetic head,material scientists try to develop a new type of multiferroic storage device by utilizing the so-called magneto-electric interaction,that is,directly using the electric field to control the magnetic moment.Stable states of ordering and high-speed flip process are the two gold standards that determine whether a new type of memory can be implemented.This requires,on the one hand,constant search for new materials and novel device structures.On the other hand,continuous development of new characterization techniques which is also important.In the field of multiferroic materials,the introduction of nonlinear optical characterization is a big breakthrough.Because the nonlinear process of optics,especially the optical second harmonic generation(SHG),is not only sensitive to the break of spatial inversion symmetry caused by the emergence of ferroelectric order,but also can intuitively characterize the magnetic order and even the anti-ferromagnetic order.This work mainly focuses on the correspondence between SHG and ferroelectric domain structures in bismuth ferrite(BFO).BFO films with different structures and domain variants were grown by pulsed laser deposition technique(PLD)and then were characterized by continuous polarization scanning of SHG.We found that BFO films with different crystalline structure(quasi-rhombohedral,quasi-tetragonal and mixed phase)and domain variants(single domain and dual domains)can be unambiguously distinguished by analyzing the SHG intensity distribution on the two polarization dimensions of polarizer and analyzer.This work provides valuable references for the utilization of SHG to characterize the temporal behavior and non-equilibrium dynamic mechanism in multiferroic materials...