Effect Of Anisotropy Of Soft Layer On The Properties Of ECC Magnetic Recording Media

The astonishing advancement of magnetic recording has brought the recordingdensity close to its physical limit.Thus,a new perpendicular magnetic recordingmedia called exchange coupled composite media (ECC media) has attracted muchattention since it can decrease the coercivity while maintaining the thermal stability.The ECC media,consisting of exchange-coupled hard and soft magnetic layers,canreach smaller coercivity through incoherent reversal of the magnetic moments of thetwo layers in an applied field,whereas the thermal stability can be maintained due tothe coherent reversal without field.The soft layer of ECC media usually possesseshigh saturation magnetization (M_s) and also high demagnetizing energy density.However,the effect of the anisotropy of soft layer has not yet been investigatedsystemically.In this thesis the effect of the anisotropy of soft layer on the switching field ofECC media was investigated by calculation using a two-moment model.It was foundthe minus anisotropy energy of soft layer is useful to the decrease of switching fieldand the sensitivity of switching field to the exchange strength between soft and hardlayers.It can also increase the optimal exchange strength,but decrease the highestGain.Assuming the anisotropy energy of soft layer is equal to its highestdemagnetizing energy,it was found the application of high Ms soft magnetic materialas the soft layer may improve the best Gain while maintaining the benefits caused byminus anisotropy.The dependence of H_sw on field angle is not affected very muchwhen the anisotropy of soft layer is minus,but worsened by plus soft layer anisotropy.These results suggest that when the demagnetizing energy of soft layer is unavoidablethe application of high Ms soft layer can help to decrease the switching field,maintainthe thermal stability,improve the uniformity,reduce the thickness of interlayer andtotal recording layer,and will not worsen the signal to noise ratio.In experimental investigation,we prepared films with the recoding layerstructure of soft/interlayer/hard by magnetron sputtering.The structure of films isC/Co-TiO₂/Pt/CoPt-TiO₂/Ru/Pt/CoZrNb/ glass-disk.By changing the sputtering gas pressure,the M_s of soft layer is adjusted successfully.For the films without a Ptinterlayer,it was found Co-TiO₂ soft layers reduce the coercivity efficiently and thelowest coercivity is about 60% of that of single recording layer.The thermal stabilityis enhanced by the strengthened intergranular exchange coupling,but the domainstructure is not affected obviously.For the films with a Pt interlayer,it was found thePt interlayer can reduce the exchange strength between soft and hard layers efficiently,so that the coercivity is decreased.And the coercivity has a small sensitivity to thethickness of Pt interlayer.It was also found that the soft layer with a high M_s is usefulto reduce the interlayer thickness of the optimal state,which can decrease thethickness of ECC media.The continuous Pt interlayer strengthened intergranularexchange coupling,that lead to the improvement of thermal stability and also theaverage domain size.Comparing to the the single recording layer film and strongexchange coupled film,the ECC film has much smaller sensitivity of coercivity tofield angle.When the field angle is 45°,coercivity decreases to about 85% of thatobtained at the angle of 0°.By measuring the remanent state MFM images of optimalECC film,it was realized that the intergranular exchange coupling is not strong,andthe reversal process of media is not the domain wall movement but the reverse ofmagnetic clusters.The experimental results suggest that the prepared ECC mediapossess favorable properties,Pt is appropriate for the interlayer of ECC media,andthe application of high M_s soft layer is useful to the reduction of recording layer.