Effect Of Oblique Deposition On Magnetization Reversal Of Epitaxially Grown Exchange Biased Fe/IrMn Heterostructures

Exchange bias refers to the phenomenon of hysteresis loop shift caused by the interfacial exchange coupling between ferromagnetic layer and antiferromagnetic layer.In recent decades,the application of the exchange bias effect has become more and more widespread,especially in magnetic recording and magnetoelectronic devices,which plays a potential role.In previous works on exchange bias systems,most of the ferromagnetic layers are in the form of polycrystalline,but the epitaxial exchange bias system has received less attention because of the difficult fabrication.In order to theoretically simulate and calculate the properties of the exchange bias systems,various theories assume that the arrangement of magnetic moments at the ferromagnetic/antiferromagnetic interface is relatively simple,ignoring the effects of grain boundaries.The epitaxial exchange bias system is similar to the ideal models in various theories because of its sharp ferromagnetic/antiferromagnetic interface and the orderly arrangement of the atoms and magnetic moments at the interface,so it is considered to be an ideal system for investigating exchange bias.For the epitaxial exchange bias system,the exchange bias effect is essentially equivalent to apply a unidirectional magnetic anisotropy and an induced uniaxial magnetic anisotropy superimposed on the intrinsic magnetocrystalline anisotropy of the epitaxial ferromagnetic layers,which together determine the magnetic switching processes and the magnetization reversal mechanism.The complicated magnetic switching processes of epitaxial exchange bias heterostructures can be well interpreted by a theoretical model based on two successive or separated 90°domain wall nucleation and propagation.In this thesis,we have grown Fe/IrMn exchange biased bilayers on single crystal MgO?001?substrates.Fe?5 nm?/IrMn?10 nm?samples were obliquely grown at three deposition angles of 0°,35°,and 50°and Fe/IrMn?10 nm?samples with different thicknesses of5,10,and 20 nm were obliquely grown at a fixed deposition angle of 50°.A remarkable uniaxial magnetic anisotropy is produced due to the self-shadowing effect caused by the oblique growth,especially for the sample grown at the deposition angle of 50°.In different directions of external magnetic field,we observed square,asymmetrical,and two-step hysteresis loops.The complicated angular dependence of magnetic switching fields can be well explained by the model of two successive or separated 90°domain wall nucleation and propagation.Fe₈₁Ga₁₉?FeGa?alloy possesses the body centered cubic structure and a lattice constant which is similar to that of Fe and displays a large magnetostrictive coefficient at small magnetic field.Based on the above-mentioned work on the epitaxial Fe/IrMn exchange bias heterostructures,we additionally fabricated epitaxial FeGa magnetic films and FeGa/IrMn exchange bias heterostructures on single crystal ferroelectric PMN-PT?001?substrates.The electric field control of magnetic switching processes was carried out for the epitaxial magnetic films and exchange biased heterostructures.Through the converse piezoelectric effect,we realized the non-volatile control of the magnetization of FeGa layer under the application of electric field on the samples.