Studies Of Ordering Behaviors And Magnetic Properties Of L1₀FePt Films

L10FePt film is considered as one of the leading candidate materials for the next generation of the ultrahigh-density perpendicular magnetic recording media, because of its large magnetocrystalline anisotropy constant and small size permitting thermal stability. Recently, extensive studies have been carried out on L10FePt films. And many progresses have been achieved. However, there are still some problems which are obstructive for practical recording applications of L10FePt film: (1) how to decrease the ordering temperature of L10FePt phase; (2) how to control the orientation of the easy magnetized axis of L10FePt phase; (3) how to improve the writing performance of L10FePt phase with high coercivity. This thesis will study the above problems. And main contents are as follows: design the initial structure of the as-deposited films to decrease the ordering temperature of L10FePt phase; obtain (001) texture of L10FePt phase using rapid thermal annealing; control the magnetic properties of exchange coupled composite media using rapid thermal annealing.Strain [FePt (2 nm)/Au (tAu nm)]20 superlattice films were prepared by magnetron sputtering at room temperature. The investigation of grazing incidence X-ray diffraction (GIXRD) shows that the strain energy stored in as-deposited FCC FePt lattice increases with increasing Au thickness. For the film with thicker Au thickness annealed at 300 oC, the strain energy stored in as-deposited FCC FePt lattice and the thermal tensile stress promoted the ordering transformation in FePt layer. Research results also indicated that when the films were annealed at relatively low temperature, the strain energy stored in as-deposited FCC FePt lattice and the thermal tensile stress could accelerate the ordered-disordered transformation of FePt phase; for the films annealed at higher temperature, thicker Au layers in the films restrained the ordering process which led to the decreases of the ordering parameters and the coercivities of the films.Atomic scale [Fe/Pt]n, [Fe/Pt/Ag]18 and [Fe/Pt/Cu]18 multilayer films were prepared using magnetron sputtering at room temperature. Effects of thickness on (001) texture, surface morphology, and magnetic properties of [Fe/Pt]n multilayer films were researched. And we also researched the effects of the doping elements on the ordering, texture, magnetic properties of the films. When [Fe/Pt]n multilayer films were annealed at 500 oC for 60 s, the films show (001) texture and the degree of dispersion increases with increasing the total thickness of the films. With increasing the total thickness of the films, the ordering parameters increase, and the surface morphologies of annealed films change from a particle-like structure to a continuous structure. The magnetic domain sizes also increase. The out-of-plane coercivities firstly decrease, then increase with increasing the total thickness of the films. And the in-plane coercivities increase sustainedly. We also researched the effects of Ag concentration on ordering, texture and magnetic properties of atomic scale [Fe/Pt/Ag]18 multilayer films. The ordering phase was formed in the films with Ag layers annealed at 350 oC. And the films annealed at 400 oC show (001) texture.ωscans indicate that L10FePt (001) texture deteriorates with increasing Ag concentration. AFM measurements show that higher Ag concentration could promote the grain growth of L10FePt. For the films annealed at 350 oC, the film with 20% Ag concentration shows the highest out-of-plane coercivity. And when the annealing temperature was increased to 400 oC, the coercivities also increase and the slopes of the out-of-plane loops at coercivity decrease with increasing Ag concentration. We also prepared atomic scale [Fe/Pt/Cu]18 multilayer films. The ordering phase was formed in the Cu doping films with total thickness below 10 nm annealed at 300 oC. And the films with Cu doping annealed at 400 oC show (001) texture. The (001) texture deteriorates with increasing Cu doping. L10FeCuPt2 phase was formed in the films with more Cu doping after annealing. TEM measurements show that doping Cu could promote the grain growth during annealing. The film with 5% Cu concentration could obtain the highest coercivities after annealing. The magnetic properties go to bad due to the form of L10FeCuPt2 phase during annealing.We researched the structure and magnetic properties of metastable FexAg100-x and FexAg100-x/Pt through annealing. The results show that the as-deposited FexAg100-x films are metastable. After annealing at 300 oC, the phase separation of metastable FexAg100-x film happened. Fe volume percent in FexAg100-x layer affects the magnetic properties of FexAg100-x/Pt films annealed at 300 oC. For FexAg100-x/Pt film with 50% Fe annealed at 300 oC, the ordering phase was formed in the film and the highest coercivities of about 3.2 kOe is obtained in the out-of-plane hysteresis loop. We also researched the effects of annealing temperature and time on the structure and magnetic properties of FexAg100-x/Pt films. The high annealing temperature could improve the ordering parameters and magnetic properties. And the longer annealing time could enhance the ordering parameter of L10FePt phase and affect the orientation of L10FePt phase.The effect on Fe layer thickness on the magnetic properties of Fe/L10FePt exchange coupled composite recording (ECC) media was investigated. The out-of-plane coercivity of Fe/L10FePt film with 1 nm Fe increases compared with single layer L10FePt film. The out-of-plane coercivities of Fe/L10FePt film decrease with further increasing Fe thickness. The out-of-plane hysteresis loop of Fe/L10FePt film with 8 nm Fe shows the two phase behavior. We also researched the variations of the structure and magnetic properties of Fe (3 nm)/ L10FePt (10 nm) films annealed at different temperature. After 300 oC annealing, the exchange coupling between hard phase and soft phase was weaken, and the coercivities increase. When the annealing temperature was further increased, Fe atoms diffused into L10FePt lattice and Fe3Pt was formed, which led to the decrease of the coercivities. The structure and magnetic properties of annealing FCC FePt(5 nm)/ L10FePt(10 nm) films were researched. For the film annealed at 400 oC, the coercivities of the film decrease, and the film became the ECC media with the graded interface. When the annealing temperature was increased to 500 oC, the film became the magnetocrystalline anisotropy graded L10FePt ECC film. With increasing the annealing temperature, the ordering parameter of the top FePt film increases, which led to the increase of the coercivities.