| L10ordered FePt thin film is considered as one of the leading candidate materialsfor the next generation of the ultrahigh-density magnetic recording media, because ofits large uniaxial magnetic anisotropy, small superparamagnetic critical size, moderatesaturation magnetization and good corrosion resistance. Although many researcheshave been reported on L10FePt films, there are still some key problems need to befurther investigated:(1) lower ordering temperature,(2) preferred orientation growthof the easy axis and (3) physical mechanism of special thermal treatment. So weobtained some interesting results basing on the three aspects in this paper.[Fe/Pt]nfilms with various period number were prepared by magnetronsputtering on300℃substrates. The as-deposited [Fe/Pt]nfilms have a good periodicstructure along the growth direction, the multilayer films show smoothsurface and clear interface.[Fe/Pt]nfilms transform from Fe/Pt superlattice structureto compositionally homogeneous L10-FePt single layer structure after400℃annealing. Ordering parameter and I001/I111trend to incline with increasing periodnumber. The preferred direction of magnetization varies from perpendicular torandom gradually. For Fe/Pt bilayer film annealed at350℃, the ordering phase wasformed. Increasing the annealing temperature could enhance the perpendicularanisotropy of the films. Magnetic field annealing has less effect on ordering ofL10-FePt, but it can refine the grain size of the films effectively, and promote uniformdistribution and exchange coupling of magnetic particles, avoid shoulder of magnetic hysteresis loop.[Fe/Pt]nmultilayer films with nominal thickness of10nm were prepared at roomtemperature, then annealed at various temperature in hydrogen gas. Effects of Fe(Pt)single layer thickness, annealing temperature and C element addition on structure andmagnetic properties of the [Fe/Pt]nfilms were investigated.[Fe/Pt]nfilms with varioussingle layer thickness annealed at600℃exhibit high (001) preferred orientation.[Fe/Pt]nfilm with0.5nm single layer thickness has largest chemical ordering valueand maximal I001/I002and I001/I111ratio, indicating strong (001) texture and highperpendicular magnetic anisotropy. The results of magnetic measurement show a highperpendicular magnetic anisotropy. For [Fe (0.5nm)/Pt (0.5nm)]nfilm, orderingdegree and perpendicular magnetic anisotropy increase with increasing annealingtemperature. The grain size of particles growing along (001) direction increase from8.1nm to11.6nm. In the [Fe (0.5nm)C/Pt (0.5nm)]nfilms,(001) preferredorientation of FePt particles improves after C doping. Although C addition has lesseffect on grain size of sample, non-magnetic C elements exit in the interstitial sites ofFePt lattice, so they isolate magnetic particles and reduce their magnetic interaction.When sputtering power of C is set as120W, squarness ratio in out-of-plane directiongets its maximum value, and magnetization mode is close to the domain wall motionover a wide-angle region.Ag (tAgnm)/FePt (20nm) films were annealed at600℃under a rapid thermalprocess. Effects of Ag underlayer thickness, heating ratio and holding time of rapidthermal process on structure and magnetic properties of the films were investigated.Random orientation dominated without Ag underlayer. In-plane coercivity is largerthan out-of-plane coercivity, indicating an ordered L10FePt film with (001)orientation. With increasing of Ag underlayer thickness, compression stress of filmsdecreases gradually. δM loops indicate that Ag underlayer can isolate FePt magneticparticles and reduce the exchange coupling. AFM images show that films are granularstructures with smooth surface and low roughness. For Ag (8nm)/FePt (20nm) films annealed with heating rate as50℃/s,it gets the minimum value of axial ratio c/a andstrongest ordering degree. For Ag (8nm)/FePt (20nm) films annealed at variousholding time, disordered-ordered transformation can be promoted.70nm FePt films were prepared by co-sputtering and annealed at magnetic field.The effect of magnetic field annealing on structure and magnetic properties of thefilms were investigated. The lattice constants a and c of the film applied to5kOemagnetic field are smaller than that of the film without magnetic field annealingcorresponding axial ratio c/a also reduces0.7％. Ordering parameter increase from0.85to0.94. So magnetic field annealing can increase the ordering degree of the FePtfilm. The total free energy reduced with magnetic field heat treatment, sodisordered-ordered transformation was improved. |
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