Magnetic Skyrmion In Nanostructure

Chiral magnets with non-central symmetric cubic structures,such as MnSi and FeGe,has always been a hot topic in the field of magnetic materials due to the rich physics originate from the coupling of a variety of free degrees like spin,orbit and lattice.In particular,in 2009,magnetic skyrmion,a topologically stable particle-like magnetic whirl,has been found in these materials.The advantageous of skyrmion,such as small size,high stability and mobility,makes it hold great promise to build future high density,high speed and low energy consumption magnetic memory devices.The preparation of chiral magnet nanostructures and the exploration of their physical properties are the key to realize the devices.Here,a top-down method is developed to controllably fabricate nanostructured samples of chiral magents.The nucleation and evolution of skyrmion in a confined geometry are fully studied,and the new kind of skyrmion material is also explored.The main results are listed as below:(1)A micro-nano processing technology to controllably fabricate nanostructured samples is developed.Using this method,nanodisk,nanostripe with varied shape are successfully prepared,which laid a solid foundation for the subsequent study of the properties of helical magnets in geometry-confined systems.(2)The field-driven evolution of skyrmions phase in highly geometry-confined system is observed directly by using high resolution Lorentz transmission electron mi-croscopy(TEM).It is found that the skyrmions exist in the form of a single chain in the nanostripe with its width comparable to the featured skyrmion size.A mechanism of edge modulation for generating skyrmions in a confined geometry at low temperatures is revealed.The discovery of single skyrmion chain has increased the feasibility of us-ing it as high density information carrier.The discovery of edge modulation mechanism may help to tailoring the ideal skyrmion properties in confined geometries.(3)The nucleation and evolution of skyrmion in a wedge-shaped FeGe nanostripe are studied in detail by using electron holography technique.It is found that geometri-cally confined skyrmion can be observed in a wide width of the wedge-shaped nanos-tripe by changing its size and ellipticity.In addition,skyrmion in the nanostripe can be transformed from helical states with twisted boundary magnetizations in a simple and efficient way.The results of this study showed that the geometrically confined skyrmion are highly flexible and ease to form,which can help to construct the skyrmion-based memory device.(4)A new kind of skyrmion material,?-Mn type FexCo1.5-xRh0.5MosN(x=0.3,0.5,1.0),are found.The magnetic properties of the x=1.0 component is studied by Lorentz TEM,which proved the existence of skyrmion.The existence area of skyrmion phase in x=0.3 and x=0.5 component are determined by magnetization measurement.In addition,the magnetic properties of Fe1-xCoxGe(x=0,0.2,0.3,0.4)samples are studied by using Lorentz TEM.It is found that with the increase of Co doping amoun-t,the size of skyrmion is gradually increased;The results of magnetic measurement of bulk material show that,with the increase of Co doping amount,the interval occu-pied by skyrmion in phase diagram is getting smaller.The discovery of skyrmion in FexCo1.5-xRh0.5Mo3N material may guide to find new skyrmion materials.The Co-doping process of FeGe provide a way to control the size of skyrmion.