Research On Controlling Magneto-Optical Properties Of Cerium Doped Yttrium Iron Garnet By Electric-Fields

Currently,the tunability of reconfigurable magneto-optical devices such as optical circulators is realized by exploiting large electric currents to drive electromagnets to generate magnetic fields.The Joule heat produced by large currents enhances the energy consumption of the devices.Utilizing an electric field to control magneto-optical effects can reduce the current and subsequently lower the energy consumption.This paper mainly investigated control of magneto-optical effect by electric fields in two kinds of new material systems.The first research is electric-field control of optical and magneto-optical properties of La_0.5Sr_0.5CoO₃/CeY₂Fe₅O₁₂ hetero-structure.At room temperature,we achieved the reversible manipulation of reflectivity of this hetero-structure by exploiting an electric field.The electric field pointing from CeY₂Fe₅O₁₂ to La_0.5Sr_0.5CoO₃ makes the electron density of La_0.5Sr_0.5CoO₃ near the interface of the hetero-structure increase,and subsequently the optical constant of it changes,making reflectivity increase.By reversing the direction of this electric field,the electron density of La_0.5Sr_0.5CoO₃ near the interface decreases and the optical constants changes in an opposite way,making reflectivity decrease.Thus,by reversing the polarity of a voltage equal to 5 V applied between two terminals of the device,the modulation amplitude of the reflectivity of La_0.5Sr_0.5CoO₃/CeY₂Fe₅O₁₂ was up to 0.12%.Theoretically,magneto-optical Kerr effect varies with reflectivity.Nevertheless,the variation of magneto-optical Kerr effect was so small that it transcended the detection limit of the measurement systems,unable to be measured experimentally.The method of modulating reflectivity by an electric field based on La_0.5Sr_0.5CoO₃/CeY₂Fe₅O₁₂ hetero-structure contributes to developing reconfigurable photonic devices.Electric-field control of the magneto-optical Kerr effect of Au/TiO_x/CeY₂Fe₅O₁₂multilayer structure is the focus of the second research.We systematically investigated the changes of reflectivity,magneto-optical Kerr effect and resistance of this structure under electric fields.Additionally,the effects of thin film thickness,the oxygen concentration of CeY₂Fe₅O₁₂ on such properties were analyzed.An operation voltage equal to 1.5 V resulted in a change of saturation magneto-optical Kerr rotation angle at635 nm wavelength up to 3.31 mdeg,corresponding to 15.1%of the pristine state,of which energy dissipation was 0.66 nJ/um² and response time was 300 s.This control was reversible and non-volatile.Besides,the device worked at room temperature and has an all-solid-state structure.The measurement of electron energy-loss spectroscopy demonstrated the structural principle of the mechanism behind the change of properties.By exploiting an electric field to drive Ti ions in TiO_x to migrate,the distribution of TiO_x content changes,modulating the refractive index of TiO_x layer.Thus,the reflectivity and mode distribution of the device are controlled,which consequently modify the magneto-optical Kerr effect.Such a method of electric field controlling magneto-optical effect based on the variation of mode distribution is general and able to maneuver the magneto-optical properties of various structures.This work offers a new route for designing and fabricating reconfigurable magneto-optical devices.