Electric Modulation Of Magnetic Properties Mediated By Strain And Charge Mechanisms In Multiferroic Heterostructures

Driven by urgent demands for electronic devices with miniaturization,low-power dissipation and high-speed response,the electric modulation of magnetism in multiferroic heterostructures has continually aroused research attention.In this work,to systematically study the involved coupling mechanisms and further strengthen the magnetoelectric coupling,various configurations of multiferroic heterostructures are taken into consideration.Mediated by various coupling mechanisms,the variation behaviors of magnetic properties in response to electric field are analyzed to reveal the interactions between these coupling effects and their underlying microscopic mechanisms.Firstly,a novel multiferroic heterostructure of SrTiO₃/Fe₃O₄/Au/PbZr_0.52Ti_0.48O₃?STO/Fe₃O₄/Au/PZT?multilayer deposited on a Nb:SrTiO₃?Nb:STO?substrate is proposed where the multiple modulations of strain-and charge-mediated converse magnetoelectric coupling effects have been investigated.By altering the position of the applied electric field,the heterostructure is divided into three functionalized parts,i.e.,Fe₃O₄/Au/PZT,STO/Fe₃O₄and STO/Fe₃O₄/Au/PZT.In such an optimized heterostructure,the strain and charge effects can be directly separated,quantified and co-regulated,and the pure strain-mediated,pure charge-mediated and the strain and charge co-mediated converse magnetoelectric coupling effects can thus be obtained,respectively.The in-plane magnetization variation behaviors induced by electric fields are different for the three individual modulations,which are closely related to the interfacial strain propagation and the interfacial charge accumulation.Furthermore,the strain and charge effects can interact with each other as the two interfacial effects coexist.Secondly,the pure strain-mediated,pure charge-mediated and strain and charge co-mediated converse magnetoelectric effects at various temperatures have also been studied by applying electric fields at three various positions of the STO/Fe₃O₄/Au/PZT multiferroic heterostructure.For the three individual effects,the magnetization anomalously varies with the temperature,which is intimately associated with the Verwey phase transition present in the Fe₃O₄.But in response to electric field,they exhibit distinct variation behaviors.The maximum coupling coefficients of pure strain,pure charge and their combined magnetoelectric coupling effects are 10.51 Oe·cm/kV??M_r/?E?,1.26 Oe·cm/kV??M_s/?E?and 2.36 Oe·cm/kV??M_s/?E?,respectively,all obtained at 115 K.Furthermore,the combination of strain and charge effects causes the nonequivalent shift of the Verwey transition temperature under reversed electric fields due to the interaction between the two coupling effects.It is also found that strong magnetoelectric couplings can be realized over a broad temperature range when the strain and charge effects simultaneously appear.Lastly,the temperature dependences of magnetization and surface magnetic anisotropy have been investigated by reversing electric fields at the interface of a Ni₈₀Fe₂₀/PbZr_0.44Ti_0.56O₃multiferroic heterostructure.Both the in-plane magnetization variation and isotropic ferromagnetic resonance field suggest that the magnetoelectric coupling effect arises from the interfacial accumulation or depletion of spin-polarized electrons,rather than the strain.As the temperature decreases,the ferromagnetic resonance field shifts left and the surface magnetic anisotropy deduced from the shift of ferromagnetic resonance field increases faster than the saturation magnetization.The strong temperature dependences of magnetization and surface magnetic anisotropy are related to the change in the spin-polarized electron density due to the electron thermal motion and the phonon scattering.