C.Y. Chou

Effects of Ag buffer layer on the microstructure and magnetic properties of nanocomposite FePt∕Ag multilayer films

The face-centered-tetragonal L10FePt films with (001) preferred orientation has perpendicular coercivity (Hc⊥) of about 2462Oe that can be achieved by stacking a structure of (FePt4nm∕Ag2nm)5 multilayer films on the 5nm thick MgO underlayer and annealing at 600°C for 30min. It is found that both the perpendicular anisotropy and coercivity of (FePt4nm∕Ag2nm)5 multilayer films are enhanced by introducing an Ag buffer layer (≦20nm) between the (FePt4nm∕Ag2nm)5 films and the MgO underlayer. When introducing an Ag buffer layer of 20nm thickness, the Hc⊥ value of the MgO5nm∕Ag20nm∕(FePt4nm∕Ag2nm)5 multilayer films is observed to increase from 2462to4731Oe, which has significant potential as perpendicular magnetic recording media for high-density recording.

Magnetoresistance and microstructure of the sintered Ni doped Fe/sub 3/O/sub 4/ ferrites

Sintered Ni doped Fe/sub 3/O/sub 4/ ferrites were prepared by mixing Fe/sub 3/O/sub 4/ powder with NiO powder and compressing into pellet, then sintering in argon atmosphere. The contents of Ni in the sintered samples were between 0 at.% and 5.08 at.%. The effects of the Ni content, sintering temperature and sintering time on the magnetoresistance (MR) and microstructure of sintered Fe/sub 3/O/sub 4/ ferrites were investigated. X-ray diffraction and chemical titration analysis of Fe/sup 2+/ and Fe/sup 3+/ ions indicate that the nonstoichiometric phases of Fe/sub 3/O/sub 4+X/ and NiFe/sub 2/O/sub 4-Y/ were co-existed in the Ni doped sample. The optimum sintering temperature, at which the maximum MR value could be obtained, is around 1100/spl deg/C and the optimum sintering time is about 9 h for all samples. After sintering at 1100/spl deg/C for 9 h, the MR value of the undoped Fe/sub 3/O/sub 4/ ferrite is about 6% at room temperature. Maximum MR value is about 7.5% when 1.12 at.% Ni was doped. It was found that the log /spl rho/ versus T/sup -1/2/ curves of all the samples exhibit a linear relationship from the measurement of the electrical resistivity (/spl rho/) of the sintered samples between 80 K and room temperature. This implies that the MR effect is mainly spin-dependent tunneling where the electrons flow through insulating barriers of Fe/sub 2/O/sub 3/, NiFe/sub 2/O/sub 4/ or NiFe/sub 2/O/sub 4-Y/.

Magnetic properties and microstructure of low ordering temperature L10 FePt thin films

Polycrystalline Fe52Pt48 alloy thin films were prepared by dc magnetron sputtering on preheated natural-oxidized silicon wafer substrates. The film thickness was varied from 10 to 100 nm. The as-deposited film was encapsulated in a quartz tube and postannealed in vacuum at various temperatures for 1 h, then furnace cooled. It is found that the ordering temperature from as-deposited soft magnetic fcc FePt phase to hard magnetic fct L10 FePt phase could be reduced to about 350 °C by preheating substrate and furnace cooling treatment. The magnetic properties measurements indicated that the in-plane coercivity of the films was increased rapidly as annealing temperature is increased from 300 to 400 °C, but it decreased when the annealing temperature is higher than 400 °C. X-ray diffraction analysis shown that the as-deposited FePt thin film was a disorder fcc FePt phase. The magnetic measurement indicated that the transformation of disorder fcc FePt to fct L10 FePt phase was started at about 350 °C, which is c...

Improvement in hard magnetic properties of FePt films by introduction of Ti underlayer

The FePt/Ti double layer films were prepared by dc magnetron sputtering on corning glass substrates with FePt and Ti targets. The Ti underlayer with 100-nm thickness was deposited at substrate temperature 200/spl deg/C, and the FePt magnetic layer, 300 nm, was prepared at temperature from 200/spl deg/C to 600/spl deg/C for direct formation of ordered L1/sub 0/ FePt phase on the Ti underlayer. X-ray diffraction analysis showed that the [002] axis of Ti grain was perpendicular to the film plane and the FePt grains had a preferred growth of (111) plane parallel to the film plane. The degree of ordering of the FePt films increased as Ti underlayer was introduced. Magnetic property measurements indicated that the in-plane coercivities (Hc/sub /spl par//) of the FePt/Ti films in which FePt films was deposited at different temperatures were all higher than that of FePt single layer film without Ti underlayer. When the deposition temperature of FePt film was fixed at 600/spl deg/C, the Hc/sub /spl par// value of the FePt single layer film was 3.1 kOe, and it increased to 7.3 kOe as 100 nm Ti underlayer was introduced.

Microstructure and coercivity of granular nanocomposite FePt-Ag multilayer films

The face-centered-tetragonal granular L1/sub 0/FePt nanoparticles with large in-plane coercivity (Hc/sub ///) of about 3923 Oe can be achieved by an Ag-capped layer of 5-nm thickness deposited onto the FePt magnetic layer, with thickness of 20 nm, after annealing at 400/spl deg/C for 30 min. The perpendicular coercivity (Hc/sub /spl perp//) of the films is increased by increasing the annealing temperature (T/sub s/), and the Hc/sub /spl perp// value is about equal to the Hc/sub /// value when the annealing temperature is increased to 600/spl deg/C. TEM-energy disperse spectrum analysis reveals that the Ag mainly distributed at the grain boundary of FePt and results in the isolation of the FePt grains as well as the increase of the grain boundary energy, which will enhance coercivity and change the preferred orientation of the FePt film.

Effects of Mg doping and sintering temperature on the magnetoresistance of sintered Fe/sub 3/O/sub 4/ ferrites

In this paper, we improve MR value of the sintered Fe/sub 3/O/sub 4/ ferrite at room temperature, and microstructure on its magnetoresistance at room temperatures were investigated.

Microstructure and magnetic properties of the FeTaCN nanocrystalline thin films

FeTaCN films were deposited on quartz substrates by cosputtering of Fe and TaC targets at room temperature with different N2 flow rate ratios in the sputtering gas. The as-deposited films were postannealed in vacuum for 30 min at various temperatures. The effects of annealing temperature on the N2 flow rate ratio and film thickness on the magnetic properties and microstructure of the film were investigated. X-ray diffraction and transmission electron microscopy analyses show that the as-deposited FeTaCN film has a nanocrystalline structure or mixing phases of nanocrystalline and amorphous. Nanocrystalline as-deposited film with good soft magnetic properties (in-plane coercivity Hc∥=1∼2 Oe and 4πMs=12–14 kG) can be obtained by controlling the N2 flow rate ratio and film thickness. The soft magnetic properties can be improved by postannealing the as-deposited film at 200–300 °C as the N2 flow rate ratio is higher than 5 vol %. For the Fe71.03Ta6.1C7.2N15.67 film, the Hc∥ value decreases as the film thicknes...

Effects of CrRu Underlayer and CrRu Capped Layer on the Microstructure and Magnetic Properties of FePt Films

The magnetic properties and microstructure of CrRu/FePt bilayer and CrRu/FePt/CrRu trilayer deposited by dc magnetron sputtering on preheated natural-oxidized Si (100) wafer substrates were studied. It is found that both the in-plane coercivity (Hc//) and grain size of the FePt film increase with increasing the thickness of CrRu underlayer. The Hc// value of the FePt film is further increased but the grain size is decreased as adding a CrRu capped layer on the FePt film. The granular L10 FePt nanoparticles with in-plane coercivity of 2300 Oe and isolated uniform size of 6.61 nm are achieved from the CrRu(15 nm)/FePt(25 nm)/CrRu(4 nm) film deposited at a low substrate temperature of 350 degC

Magnetic properties of CoTb/FePt(001) nano-bilayer films

The magnetic properties and microstructure of CoTb/FePt bilayer films are investigated. The magnetic anisotropy of the Co70Tb30/FePt(001) film is perpendicular to the film plane. The saturated magnetization (Ms) and perpendicular coercivity () of the Co70Tb30/FePt(001) bilayer films are higher than those of single-layered Co70Tb30 films. The and Ms are 5450 Oe, and 403?emu?cm?3, respectively. As the temperature is increased to 200??C, there is a rapid decrease in the value.

Magnetic Properties and Microstructure of TbFeCoAg Amorphous Thin Films

The effect of Ag content on the magnetic properties and microstructure of Tb19.05Fe22.01Co58.94-xAgx film (x=0–18.51 at. %) were investigated. As judged from X-ray diffraction and transmission electron microscopy analyses, as-deposited Tb19.05Fe22.01Co58.94-xAgx films were amorphous. It was found that the addition of a small amount of the nonmagnetic element Ag into TbFeCo increases the saturation magnetization (Ms) and perpendicular coercivity (Hc⊥) of the film. For a Tb19.05Fe22.01Co55.75Ag3.19 film, the Ms is 268 emu/cm3, the perpendicular squareness is 0.94 and the Hc⊥ is 2058 Oe at room temperature. The Hc⊥ of the Tb19.05Fe22.01Co55.75Ag3.19 film decreases to approximately 40 Oe as temperature is increased to 200 °C. This film has potential for heat-assisted magnetic recording media applications.