Resonant Modes And The Magnetization Dynamics Of A 180° Transverse Magnetic Domain Wall In Ferromagnetic Nanostripe

Magnetic materials have broad application prospects in magnetic storage devices and logic devices,because of the response characters of their magnetic resistance or domain wall to the applied magnetic field.The driving characteristics of 180°transverse domain wall in a soft magnetic nanostrip under an applied constant magnetic field,the resonance characteristics under an applied alternating magnetic field,and the magnetization dynamic processes under a simultaneously applied alternating resonant field and constant driving field are researched by LLG micro-magnetic simulation software in this thesis.While applying a constant field along the length direction of nanostrip,the 180°transverse domain wall will propagates along the direction of the constant field,that is,the region of the magnetic moment which is in the same direction as the constant field in the nanostrip will expand.When the field strength increases to a certain amplitude,the transverse domain wall will produce an anti-vortex core in the narrower end of the domain wall,then the core will be driven laterally by gyro-force.Thus the propagation velocity of the transverse domain decreases sharply,the Walker breakdown occurs.So how to restrain the nucleation of the anti-vortex and its lateral propagation,to avoid the phenomenon of Walker breakdown,to improve the propagation velocity and stability of the transverse domain has been a hotspot.We accidentally found that in the case of applying a constant field along+x direction to a narrower strip width,the magnetic moment of domain wall region rotates in the my-mzplane.When the magnetic moment of domain wall region is in the 1st&3rd quadrants,the domain wall propagates along the+x direction;while in the 2nd&4th quadrants,the domain wall will propagate along-x direction.We choose the direction of the applied alternating magnetic field along the length,width and thickness direction of the nanostrip,and we observe twisting mode,multinodal domain mode,breathing mode,translational mode and novel accordion mode of the domain wall.When the alternating magnetic field is applied along the strip width direction,the width of the transverse domain top and bottom ends presents an antiphase vibration,we named it accordion mode.Further research shows that,while applying a constant driving magnetic field along the length direction of the nanostrip,superposing simultaneously an alternating magnetic field of resonant frequency to stimulate the twisting mode,translational mode or accordion mode of the magnetic domain wall,could significantly restrain the appearance of the Walker breakdown,thus greatly improve the propagation distance of the magnetic domain wall.The mechanism that the resonance motion of the domain wall can suppress the Walker breakdown is that these specific vibration modes can impede the birth of anti-vortex core in the narrow width end of the transverse domain wall,thus avoiding the complex deformation of the transverse domain which caused by the precession motion of the anti-vortex core.