Preparation And Ultrafast Spin Dynamics Study Of Perpendicular Magnetic Recording Media

With the development of information age,the volume of information is consistently increasing very fast,and the transmission speed is also accelerating very fast.Hard disk recording is the best storage medium,so people are keeping asking for higher areal density and faster information processing speed.Perpendicular magnetic recording has been a super star in the hard disk industry for the past two years,and it receives widespread concern.In order to truly realize 1Tbit per square inch storage density,it requires constant innovation and development of new materials to meet the needs of the public.Magneto-optical Kerr effect with time-resolved pump-probe technique can be used to study the transient reversal of the magnetic spin and to explore the limit of magnetization reversal speed in magnetic systems.It has great impact on the magnetic recording industrial such as heat-assisted magnetic recording(HAMR).In order to improve the signal to noise ratio,magnetic recording media must be of granular configuration.However,ultra-fast spin dynamics research on magnetic granular film has not yet been reported.This research work was carried out under the above background.The dissertation mainly includes the following contents.Firstly,we carried research on effect of seed layer texture and heat treatment on CoCrPt perpendicular magnetic recording media.We got optimized parameter of making better CoCrPt media.Both Cu and Cr seed layer materials are observed to greatly improve the coercivity of CoCrPt media,compared with samples grown on bare glass.These two types of materials brings to different nucleation field of the CoCrPt media.Nucleation field of sample with Cr seed layer is negative,which is due to the domain wall displacement dominated magnetization reversal.Nucleation field of sample with Cu seed layer is positive,which is due to the collective rotation dominated magnetization reversal.We finally optimized the sample through three aspects:annealing time,growth temperature and seed layer thickness.Secondly,we studied the L1₀ FePt-CoCrPt perpendicular exchange coupled system.CoCrPt granular soft layer is very effective in reducing the writing field of FePt hard layer.When the thickness of soft-magnetic layer is smaller than a critical value,the bilayer will act as a rigid magnet.When the thickness of soft layer becomes larger,the bilayer will act as an exchange spring media.For exchange spring media, the magnetization reversal process is divided into three stages.It begins with a reversible magnetization reversal in the soft layer and forms a N(?)el domain wall. Then,the domain wall is squeezed to the hard layer.Finally,multi-domain is formed in the hard layer to reduce the total energy of the system.Thirdly,we studied the spin dynamics and transient magnetic softening in L1₀ FePt granular films.After the pump excitation,the reflectivity,Kerr angle,coercivity, rectangular degree and the magnetization reversal mode all undergo rapid change followed by the subsequent slow recovery.The thermal response strength of three samples goes like:FePt-MgO granular films＞FePt single layer＞FePt-Ag granular films.The thermal demagnetization in FePt-Ag granular films is smaller than FePt single layer.It is mainly due to allocation of incident pump energy by the free electrons in Ag,and the energy absorbed by FePt becomes smaller.What is more important is that FePt-MgO granular films have greater magnetic thermal response.It is due to the existence of surface plasmon resonance which brings to higher electron temperature,and consequently better magnet softening effect.