S.C. Chen

Domain wall dynamics in the presence of an external magnetic field normal to the anisotropy axis

Abstract The generalized Slonczewski equations have been applied to study the influence of the field normal to the anisotropy axis on the Walker critical field, critical velocity and the maximum velocity of the steady-state domain wall motion. It is shown that the maximum value of the drive field dependence of the velocity of the steady-state motion is the Schlomann limiting velocity. The dependences of the Walker critical field and velocity as well as the Schlomann limiting velocity on the field normal to the anisotropy axis have been obtained.

Microstructure and magnetic properties of nanocomposite FePtCr–SiN thin films

[(FePt)100−xCrx]100–δ –[SiN]δ nanocomposite thin films with x=0–25 at. %, and δ=0–30 vol. % were fabricated on a natural-oxidized Si(100) substrate by dc and rf magnetron cosputtering of FePt, Cr, and Si3N4 targets. The thickness of the films was kept at 10 nm in order to examine the possibility for applying in high-density magnetic recording media. Transmission electron microscopy (TEM) and electron diffraction analyses indicated that the face-centered-cubic (fcc) γ-phase FePt, body-centered-cubic (bcc) Cr, and amorphous SiN coexisted in as-deposited films. The as-deposited films were annealed in vacuum between 350 and 750 °C for 30 min, and then ice-water quench cooling, in order to transform the soft magnetic fcc γ-FePt phase to the hard magnetic face-centered-tetragonal (fct) γ1 phase. Cr was added to inhibit the FePt grain growth, and was observed by TEM and energy disperse spectrum analysis in the grain surface area of FePt grains. The TEM observation indicated that the structure of the film was an ...

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...

GeCu Thin Films for Inorganic Write-Once Media

The Ge100-xCux thin films (x=50 at.%-69 at.%) were deposited on nature oxidized Si (100) wafer by dc co-sputtering of Ge and Cu targets. Microstructures was analyzed by X-ray diffractometer. The optical and thermal properties were measured from static test. It was found that the as-deposited phase was single supersaturated epsiv-Cu3Ge phase and it was transformed to Ge and epsiv-Cu3Ge coexisting phases after annealing at 400degC. The reflectivity of as-deposited film was higher than that of annealed film

Enhancement of tunneling magnetoresistance through a magnetic barrier

Magnetoresistance of a spin-filter junction is theoretically studied and a large polarization of the tunneling current is produced from spin-dependent barrier. Two kinds of spin-filter junctions are proposed and their magnetoresistance ratios are much larger than that of the conventional spin polarized tunneling junction at appropriate conditions.

Preparation and Properties of P-Type Transparent Conductive NiO Films

The NiO-Cu composite films with various Cu contents of 0 – 18.17 at.% are deposited on glass substrate. An ultra high electrical resistivity (ρ) is obtained and cannot be detected by four point probe measurement when the Cu contents in the films are lower than 6.97 at.%. The ρ value is reduced significantly to 35.8 Ω-cm as Cu content is increased to 9.18 at.%, and it further decreases to 0.02 Ω-cm when the Cu content further increases to 18.17 at.%. The Hall measurement for all Cu-doped NiO films show p-type conduction. In addition, the transmittance of NiO films also decreases continuously from 96 % to 43 % as Cu content increases from 0 to 18.17 at.%. The XRD patterns of Cu-doped NiO films only appear NiO peaks and the crystallinity of NiO films becomes worse as Cu content is added to above 6.97 at.%. Large amount of lattice sites of Ni2+ ions in NiO crystalline are replaced by the Cu+ ions that leads to p-type conduction and result in the degradation of crystallinity for NiO-Cu composite films having higher Cu content.

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.

Reduction of grain size and ordering temperature in L1/sub 0/ FePt thin films

In this research, a more effective procedure for reducing the ordering temperature of the L1/sub 0/ FePt thin films is proposed. These thin films, with thickness varying from 10 nm to 200 nm, are prepared by conventional magnetron sputtering system with a dc power supply and then postannealed in vacuum. The phases and microstructures of the films are characterized by X-ray diffraction (XRD) with Cu-K/spl alpha/ radiation and transmission electron microscopy (TEM) bright field image, respectively. TEM bright field images show that the films have average grain sizes of about 6 nm. XRD patterns show that there is no evidence that ordered structure exists in the film when annealing temperature (T/sub an/) /spl les/ 300/spl deg/C. For T/sub an/ /spl ges/ 350/spl deg/C, the disordered fcc FePt phase transforms into the ordered L1/sub 0/ FePt phase. Vacancies into the film are formed easily due to the high deposition rate process in this investigation. Some extra energy is introduced into the as-deposited film during deposition and reduced the order-disorder energy barrier.

Effect of Thicknesses on the Microstructure and Magnetic Properties of CoPt Thin Films

The microstructures and magnetic properties of CoPt thin films with thicknesses between 1 and 20 nm deposited on amorphous glass substrate and post-annealing at 600°C for 30 min were investigated. The morphology of CoPt thin film would change from a discontinuous nano-size CoPt islands into a continuous film gradually as the film thickness was increased from 1 to 20 nm. The formation mechanism of the CoPt islands may be due to the surface energy difference between the glass substrate and CoPt alloy. Each CoPt island could be a single domain particle. This discontinuous nano-island CoPt recording film may increase the recording density and enhance the signal to noise ratio while comparing with the continuous film. The as-deposited 5 nm CoPt film revealed the separated islands morphology after annealing at 600°C for 30 min. This nano-size CoPt thin film may be a candidate for ultra-high density magnetic recording media due to its discontinuous islanded nanostructure.