J. G. Na

Rapid ordering of Zr-doped FePt alloy films

The magnetic properties and microstructural evolution of Zr-doped FePt alloy films prepared by dc-magnetron sputtering were investigated. Compared to an undoped Fe59Pt41 binary film, Zr-doped FePt alloy films showed accelerated ordering transformation kinetics accompanying smaller grains: we were able to fabricate a Zr-doped FePt film [e.g., (Fe59Pt41)97Zr3] possessing very fine grain size (5 nm in average) and high coercivity (7.3 kOe) within 10 min annealing at 500 °C. It is thought that the point defects and lattice strain introduced by Zr-doping activated the nucleation rate of the ordered phase. In particular, for Zr-doped FePt films containing less than 45 at. % Pt, the ordered L10 phase was decomposed into a disordered phase after excessive annealing due to the formation of a Pt–Zr compound, most likely Pt3Zr, that reduces the effective Pt content in the ordered phase.

Effects of annealing condition on the structural and magnetic properties of FePt thin films

Equiatomic FePt films were deposited by a dc sputtering method and annealed in the air and in a vacuum at 350/spl deg/C for up to 60 min. The order-disorder transformation occurs almost entirely within 10 min and a very high coercivity of 6.8 kOe could be obtained in the air-annealed films while the transformation occured very slowly in the vacuum-annealed films. This higher transformation rate could be also verified in the X-ray diffraction analysis. The reason for the higher rate seems to be the diffusion of oxygen atoms and possible mechanism was discussed.

Microstructural evolution and phase transformation characteristics of Zr-doped FePt films

In the present study, an emphasis was given on elucidating the details of microstructural changes in both undoped FePt and Zr-doped FePt films upon exposure to postdeposition annealing. Recently, the present authors have discovered [S. R. Lee, S. Yang, Y. K. Kim, and J. G. Na, Appl. Phys. Lett. 78, 4001 (2001)] that 3 at. % Zr doping into Fe59Pt41 films accelerated the ordering kinetics (10 min at 500 °C), accompanying high coercivity Hc of 7.3 kOe. Our transmission electron microscopy study on both Fe59Pt41 and [Fe59Pt41]97Zr3 films annealed at 500 °C for 60 and 10 min, respectively (both exhibited Hc=7300 Oe) revealed that the FePtZr film displayed excellent microstructural features: smaller average grain size (D) with narrower distribution (σ) (D=6.0 nm,σ=2.3 nm) compared with FePt (D=33.6 nm, σ=25.0 nm). For the FePtZr system, we have found that an ordered phase decomposed into disordered phases (thereby losing the high Hc) after 15 min annealing. By evaluating the long-range-order parameter S changes...

MAGNETIC AND STRUCTURAL PROPERTIES OF (CO1-XFEX)PT THIN FILMS

(Co1−xFex)Pt films were grown on a glass substrate by a rf sputtering and then annealed at 650–700 °C in a high vacuum. All the as-sputtered (Co1−xFex)Pt films deposited below 400 °C had a disordered structure and showed very low coercivities. With increasing the deposition temperature and Fe contents, the (111) texture was weakened in as-deposited (Co1−xFex)Pt ternary films. Vibrating sample magnetometer and x-ray diffraction data show that Co atoms in the L10 CoPt phase were substituted with Fe atoms. In-plane coercivities of these films decreased almost linearly with increasing Fe content which seemed to be due to the decrease of a crystalline anisotropy energy.

Microstructure and magnetic properties of oxidized Fe-Pt films with high rate order-disorder transformation

Structural and magnetic properties of air-annealed Fe/sub 1-x/Pt/sub x/ films with a high rate order-disorder transformation were analyzed by transmission electron microscopy, Auger electron microscopy, Rutherford backscattering spectroscopy and vibrating sample magnetometer. The air-annealed films consisted of three layers, that is, crystalline Fe oxide layer, Fe-Pt upper layer with small grains, and Fe-Pt bottom layer with large grains from the film surface. Those layers were nonmagnetic, magnetically hard, and with magnetically hard and soft phase, respectively. The Fe content in Fe-Pt metallic layer decreased and then increased with increasing film depth from the oxide/metal interface.

Fabrication and magnetic properties of metal/cobalt ferrite composite thin films

To improve the saturation magnetization (Ms) of cobalt ferrite thin films, metal/cobalt ferrite composite thin films were prepared by controlling the sputtering conditions such as oxygen concentration in sputtering gas, substrate temperature, composition of the thin films. With decreasing the oxygen ratio from 50% to 5% in sputtering gas and increasing the substrate temperature from room temperature to 400 °C, the Ms of the thin films was increased and the coercivity (Hc) decreased. The result was attributed to deposition of the metal/cobalt ferrite thin films. With increasing the metal ratio in the thin films, preferred orientation of (111) of cobalt ferrite was worsened in the thin films. The metal deposited in the thin films was identified as cobalt with (002) preferred orientation. In higher cobalt content than the stoichiometric composition of CoFe2O4, the thin films with high Ms and Hc could be deposited in the wide substrate temperature range of 200–400 °C. We can prepare the metal/cobalt ferrite c...

Surface topology and magnetic properties of FePt alloyed thin films

Dependency of Ar pressure on the surface topology and magnetic properties of as-deposited and air-annealed 120 nm thick FePt thin films were investigated. The higher the Ar pressure was, the rougher the surface of as-deposited films became. After annealing in the air, the surface became much rougher which was due to formation of Fe oxide on the surface. The oxidation was much accelerated in the films with rougher surface. This accelerated oxidation resulted in a high order-disorder transformation rate and higher coercivity.

ANISOTROPIC GIANT MAGNETORESISTANCE INDUCED BY MAGNETOANNEALING IN FE-AG GRANULAR FILMS

The effects of magnetoannealing on the giant magnetoresistance (GMR) in FexAg100−x granular films (X=15, 26, 29, 33, 37, and 60) were investigated. The thin films were annealed in a presence of magnetic field of 3 kOe at different temperatures of 300, 400, and 500 °C using various annealing times. It is found that the anisotropic GMR characteristics were developed when Fe‐Ag granular thin films were annealed in the presence of a magnetic field. The anisotropic GMR characteristics of the thin films were closely related to the magnetic anisotropy developed along the field direction during magnetoannealing.

A Mössbauer effect study on the acicular cobalt ferrite particles

The causes of the coercivity enhancement and the coercivity instability of acicular cobalt ferrite particles containing 0–9.2 wt % Fe2+ ions under the influence of magnetic field and temperature were investigated by means of transverse magnetic field annealing, torque, and Mossbauer experiments. The coercivity enhancement and the instability of Co modified iron oxide particles are closely related to the uniaxial magnetic anisotropy. A Fe2+‐CO2+ pair model was proposed to explain the uniaxial magnetic anisotropy of Co modified iron particles. To verify the nature of the Fe2+‐Co2+ pair, the probability of one or more Co ions appearing in the neighborhood of a B site Fe2+ ion was calculated using the chemical composition, the Mossbauer parameters, Pi(Fe+2) and Pi(Fe+3) and discussed conditions for forming the pair between the nearest‐neighbor Co2+ and Fe2+ ion.

High coercivity and small grains of Fe/sub 60-x/Pt/sub 40/Cu/sub x/ ternary thin films

Summary form only given. L1/sub 0/ FePt thin films with high coercivity and remanence are generally considered a good potential material for use as a high density recording medium. The medium also requires isolated small particles to reduce inter-grain magnetic interactions, which leads to lower noise. Many third metallic elements such as Cr, Ti, W, and etc were added to achieve these goals. However, decrease of coercivity was unavoidable in these metallic films. In this paper we first report a high coercivity as well as smaller grains of Fe/sub 60-x/Pt/sub 40/Cu/sub x/ ternary thin films. Coercivity higher than 10 kOe and small grains of 30 nm could be achieved when 4 at. % Cu were added in 50 nm Fe/sub 60/Pt/sub 40/ films. For these, 50 nm Fe/sub 60-x/Pt/sub 40/M/sub x/ (M=Cu, Cr) thin films were sputtered from Fe-Pt-(Cu, Cr) composite target on the coming 7059 glass by DC magnetron sputtering.