The Research On Voltage Control Of Magnetic Moment In Antiferromagnetic Materials

The new multiferroic heterojunction can achieve the flip of the modulated magnetic moment through the inverse magnetoelectric coupling effect,using the huge equivalent magnetic field generated by the strain in the magnetic material.Since this inverse magneto-electric coupling effect only uses the voltage to induce the change of magnetic moment orientation in the magnetic material by deformation of the piezoelectric material,this method does not generate any current so there is no heat loss,and it is an ultra-low energy modulation method,which also provides a new way to solve the growing energy consumption and heat dissipation problems of the current integrated whole machine system.Theoretical calculations show that Ir Mn and Pt Mn,which are commonly used in magnetic storage units,have larger magnetostriction coefficients than ferromagnetic materials,so if the inverse magnetoelectric coupling effect can be used as the basis and the antiferromagnetic material as the intermediate bridge,the magnetic moment of the ferromagnetic layer of the storage unit can be driven by the strain regulation of the magnetic moment of the antiferromagnetic material.It can not only solve the problem that ferromagnetic materials without hysteresis expansion coefficient can not realize magnetoelectric coupling modulation,but also expand the inverse magnetoelectric to antiferromagnetism,which provides a new way to explore voltage regulated magnetic storage under ultra-low energy consumption.Therefore,in this study,we prepare a piezoelectric substrate/antiferromagnetic layer/ferromagnetic layer heterojunction,and the effective modulation of the magnetic moment of the antiferromagnetic layer by voltage is firstly demonstrated based on the inverse magnetoelectric coupling effect,and then we applied to the giant magnetoresistive GMR spin valve unit,and the electrically controlled giant magnetoresistive effect based on the rotation of the magnetic moment of the ferromagnetic layer by the modulation of the exchange bias field is initially obtained,which provides a new way for the modulation of the antiferromagnetic magnetic moment and the development of the inverse magnetoelectric coupling effect.and the development of the inverse magnetoelectric coupling effect has been laid a certain foundation.The main research of this thesis is as follows.First,the study establishes the energy relationship of magnetic moment flip of ferromagnetic/antiferromagnetic exchange-biased bilayer film based on the single-domain model,and introduces the equivalent field generated by the inverse magnetoelectric coupling effect into it.We obtains the effects of exchange-biased field H_EB,inverse magnetoelectric coupling equivalent field H_S,and ferromagnetic film anisotropy field on the magnetic moment flip of exchange-biased bilayer film through modeling and simulation,which provides a basis for the subsequent study of inverse magnetoelectric coupling effect regulation of antiferromagnetic magnetic moment angle and direction change extraction in the subsequent inverse magnetoelectric coupling effect regulation study provides an effective judgment method.Secondly,the PMN-PT/isolation layer/ferromagnetic layer multiferroic heterojunction was firstly prepared with single-crystal PMN-PT piezoelectric material as the substrate.By changing the thickness of the bottom isolation layer,this thesis makes a comparative study on the materials with larger magnetostrictive coefficient NiCo and smaller magnetostrictive coefficient NiFe.It is found that for Nico material,when PMN-PT is applied with a voltage of 6 k V/cm,the response distance of inverse magnetoelectric coupling is about 230 nm;For NiFe materials,the response distance of inverse magnetoelectric coupling is 115 nm when PMN-PT applies a voltage of 6k V/cm.Then PMN-Pt/Cu/Ir Mn/NiFe multiferroic heterojunction was prepared.The thickness of Cu/Ir Mn was set to be greater than the inverse magnetoelectric coupling response distance of NiFe film.Through the test of exchange bias field under strain,it is confirmed that the inverse magnetoelectric coupling effect can effectively regulate the antiferromagnetic magnetic moment.Combined with the single domain model,it is confirmed that the modulation angle of antiferromagnetic Ir Mn is about 20°.Finally,the bottom peg-tied GMR spin-valve cell is prepared on PMN-PT.By adjusting the voltage on the strain substrate,the magnetoresistance modulation of GMR spin valve storage unit under zero magnetic field is realized,providing a prototype of magnetic storage cell based on the modulation of antiferromagnetic magnetic moment.