| Amorphous Sm-Co films with uniaxial in-plane anisotropy have a great potential for application in information storage and spintronics.How to make the issue of “the application of amorphous Sm-Co films” move from the research stage to the practical stage,and how to obtain the amorphous Sm-Co films with uniaxial in-plane anisotropy in a no-external-magnetic-field way,are the focus of Sm-Co material researchers.In this thesis,the amorphous Sm-Co thin film is taken as the research object,and the strain is introduced through various means.The effects of the strain,caused by the multi-field coupling and the pre-strain of the substrate,on the anisotropy of the amorphous Sm-Co thin films are systematically studied.The main contents are as follows:1.Amorphous Sm-Co thin films were grown on(011)-cut PMN-PT substrates,and multiferroic heterostructures with both hard magnetic and ferroelectric properties were prepared to study the anisotropic nonvolatile magnetization controlled by electric field in amorphous Sm-Co thin films.It can be found that when an electric field is applied in the out-of-plane [011] direction,the magnetization process of the amorphous Sm-Co thin film along the [100] direction(hard axis direction)becomes easier,and the magnetization process along the [01-1] direction(easy axis direction)becomes harder.Besides,the nonvolatile modulation and the two-state memory effect can be achieved under the action of both the bipolar electric field and the unipolar electric field.Detailed analysis shows that the generation of the induced effective uniaxial magnetic anisotropy field and the variation of the Sm-Co and Co-Co directional pair orderings are the two reasons for the anisotropy tunabilities of the amorphous Sm-Co films.In addition,the irreversible R-O phase transition in PMN-PT substrate plays an important role in the nonvolatile modulation.The anisotropy nonvolatile control of magnetization for Sm-Co amorphous films opens a new avenue for developing multifunctional information storage and novel spintronics devices based on the hard magnetic materials.2.Amorphous Sm-Co thin films were grown on(011)-cut PMN-PT substrates to study the multilevel nonvolatile memory effect in amorphous hard magnetic Sm-Co/PMN-PT(011)heterostructure.It can be found that the multilevel nonvolatile memory effect can be realized in the amorphous Sm-Co/PMN-PT(011)heterostructure by the ingenious use of the polarization switching in the PMN-PT(011)substrate,and the method is not unique.We propose and use two new methods,quasi-unipolar-method and quasi-minor-loop-method,to achieve this goal.In quasi-unipolar-method,different reversing electric fields lead to different Mr(-0),and the difference among these varied Mr(-0)and Mr(+0)guarantees the implementation of multilevel memory effect.In quasi-minor-loop-method,different maximum electric fields lead to different Mr(-0)/Mr(+0)pairs,and these separated Mr(-0)/Mr(+0)pairs provide a possibility for the multilevel magnetic memory effect.The present work promotes amorphous Sm-Co film to be used in multifunctional information storage and novel spintronic devices based on hard magnetic materials.3.In the absence of an external magnetic field,amorphous Sm-Co films are grown on(011)-cut single crystal substrate with different lattice constants,(001)-cut single crystal substrate with different lattice constants and flexible substrate with different pre-strain,so as to study the effect of pre-strain brought by the substrate on the magnetic properties of amorphous Sm-Co films.It can be found that the amorphous Sm-Co thin films grown on(011)-cut single crystal substrates exhibit uniaxial in-plane anisotropy,and the anisotropy constant increases as the lattice constant of the substrate decreases.Besides,the amorphous Sm-Co thin films grown on PET flexible substrate are isotropic,and the magnetization process becomes easier/harder with the increase of compressive/tensile strain.Detailed analysis shows that(011)-cut single crystal substrates can provide anisotropic pre-strain to the amorphous Sm-Co film grown on it,which greatly promotes the growth of the ferromagnetic domain along the long axis direction in the amorphous Sm-Co thin film,thus leading to the generation of the uniaxial in-plane anisotropy in the amorphous Sm-Co thin film.The difference in lattice constants of different substrates will affect the Sm-Co and Co-Co directional pair orderings in the amorphous Sm-Co thin film,which leads to the adjustable anisotropy constants.In addition,the reverse splash treatment enhances the binding effect of the PET flexible substrate on the amorphous Sm-Co thin film grown on it,which makes the magnetization process of the amorphous Sm-Co film show a synergism in the direction parallel to and perpendicular to the pre-strain.Due to the negative magnetostrictive properties of the amorphous Sm-Co thin films,the magnetization process becomes easier/harder with the increase of the compressive/tensile strain. |
