Wei Fu-Lin

Excellent soft magnetic properties realized in FeCoN thin films

FeCoN soft magnetic thin films are prepared by using the reactive direct-current magnetron sputtering technique. It is found that the addition of N2 can reduce the coercivity of the FeCoN film, and excellent soft magnetic properties can be obtained when the ratio of N2 flow to total gas flow is 10%. The influences of texture, grain size, and stress on the magnetic properties and the high-frequency behaviors of the films are also discussed.

Micromagnetic Simulation of Transfer Curve in Giant-Magnetoresistive Head

The transfer curve of the giant-magnetoresistive (GMR) magnetic head represents its most important property in applications, and it is calculated by the micromagnetic modeling of the free layer and the pinned layer in the heart of the GMR head. Affections of the bias hard magnetic layer and the anti-ferromagnetic pinning layer are modeled by effective magnetic fields. The simulated transfer curve agrees with experiment quite well, therefore the values of these effective magnetic fields can be determined by the model. A synthetic antiferromagnetic spin valve structure GMB. head is also analyzed for comparison.

Magnetic force microscopy study of alternate sputtered (001), oriented L1(0) phase FePt films

We present a magnetic force microscopy study of alternate sputtered (001) oriented L1(0) phase FePt films. It is found that the root-mean-square value of phase shift of magnetic force images, can be used to characterize the perpendicular anisotropy for a series of specimens. Therefore, the considerable improvement of the perpendicular anisotropy after post-annealing can be characterized. In addition, the magnetic properties, magnetic and crystalline microstructures before and after post-annealing are compared for the typical [Fe5nmPt5nm](10) film with substrate temperature T-s = 500 degrees C, single layer thickness d = 5 nm and total layer thickness D = 100 nm to confirm the effect of post-annealing on improving the perpendicular anisotropy for Fe-Pt films.

A micron-sized GMR sensor with a CoCrPt hard bias

A GMR (giant magneto-resistive) spin valve sensor for magnetic recording has been designed in an attempt to solve the Barkhausen noise problem in small-sized GMR sensors. In this study, the GMR ratio of the top-pinned spin valve is optimized to a value of 13.2%. The free layer is magnetized perpendicular to the pinned layer by a CoCrPt permanent magnetic bias so that a linear magnetic field response can be obtained. An obvious improvement on performance is observed when the permanent magnetic bias is magnetized, while the GMR sensor has a steadier MR–H loop and a smaller coercive field.

Reduction of Ordering Temperature of FePt–Al2O3 Thin Films by N2 Addition During Sputtering

We investigate the effect of N-2 addition during sputtering on the microstructure and magnetic properties of FePt-Al2O3 thin films. The texture of FePt phase in FePt-Al2O3 thin films changes from (111) to a more random orientation by N-2 addition during sputtering. The ordering temperature of FePt phase reduces about 100 degrees C with appropriate N-2 partial pressure. A larger coercivity of 6.0 x 10(5) A/m is obtained with N-2 partial pressure about 15%. Structural analysis reveals that a small quantity of Fe3N phase forms during sputtering and the release of N atoms during the post annealing induces a large number of vacancies in the films, which benefits to the transformation of FePt phase from fcc to fcc.

Evolution of structure and magnetic properties of nanocrystalline FeXN thin films via Ta and Al addition

Nanocrystalline FeAIN and FeTaN films are prepared by direct growth and crystallization of their as-deposited amorphous films, respectively. The two films both show soft magnetism of nanocrystalline, but their uniaxial anisotropy is observed to be different from each other. Measurements of microstructure reveal that Ta addition leads to higher N-solubility in these films, and results in larger lattice dilation and more compressive stress. The uniaxial anisotropy is the consequence of the anisotropic distribution of interstitial N atoms in an α-Fe lattice. Al is easy to react with nitrogen, therefore the α-Fe is purer in the FeAIN film than in the FeTaN film and the stress is tensile in the FeAIN film. The difference in anisotropy may be attributed to the different microstructures in both films.

Study of nanocrystalline Fe-Al-N soft magnetic thin films

Fe-Al-N films were fabricated by reactive sputtering using a radio-frequency magnetron sputtering system. The effects of Al and N content and annealing temperature on microstructure and magnetic properties were investigated. The Fe-Al-N films, which have good soft magnetic properties, consist of nanocrystalline α-Fe grains and a small amount of other phases in the boundaries of α-Fe grains. The average α-Fe grain size is about 10-15nm. A slight amount of Fe-N and Al-N compounds precipitate in the boundaries of α-Fe grains and suppress their growth. Annealing improves the soft magnetic properties slightly by releasing the residual stress and reducing defects.

Influence of an Fe cap layer on the structural and magnetic properties of Fe49Pt51/Fe bi-layers

The influences of an Fe cap layer on the structural and magnetic properties of FePt/Fe bi-layers are investigated. Compared with single FePt alloy films, a thin Fe layer can affect the crystalline orientation and improve the chemical ordering of L10 FePt films. Moreover, the coercivity increases when a thin Fe layer covers the FePt layer. Beyond a critical thickness, however, the Fe cover layer quickens the magnetization reversal of Fe49Pt51/Fe bi-layers by their exchange coupling.

Synthesis and Characterization of Thin Ba-M Hexagonal Ferrite Films

It is demonstrated that Ba-M hexagonal ferrite films with a thickness of ∼100 nm and the properties required for the data recording at a superhigh density can be synthesized on an amorphous substrate. The films are obtained on SiO2/Si substrates by magnetron sputtering of a Ba-M ferrite ceramic target in a gas mixture of Ar and O2 taken at the partial pressures of 3.5 and 0.5 mTorr, respectively. In order to obtain the required crystal and magnetic structure, the films were annealed for 1 h at 700, 800, or 900°C. The experimental data show that the annealing at 800°C leads to crystallization of the amorphous deposit into a hexagonal ferrite of the Ba-M type.