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A micromagnetic theory is presented for spin-reorientation transitions in ultrathin magnetic films with normal surface anisotropy. Both discrete and continuum models are investigated and coincidence is found between the results derived from them. Two continuous transitions in spin orientation, from uniform and normal to canting, and then to uniform and in-plane, are observed as the film thickness is increased. The effects of higher-order terms in the expansions of the anisotropies compared to the dominant terms are also considered. A method for evaluating the surface anisotropy is formulated. The relation between the present micromagnetic theory and the phenomenological theory is discussed.

Switching properties of a regular square lattice of 40x40x3 [[[micro]meter].sup.3] highly uniaxial, single domain magnetic garnet pixels have been measured magnetooptically. 'Up' and 'down' switching fields, coercivities and interaction fields were measured on an assembly of hundreds of particles. Statistical analysis of the data shows the relationship between major loop parameters and mean values of the distributions. Local demagnetizing tensor elements were calculated for the non-ellipsoidal geometry and the interaction fields from different neighbors were computed. The importance of the effect of the geometry, shape and size of particles on the switching properties is demonstrated. The agreement with experimental values is very good. The simplicity of this model system is attractive for studying artificially structured 2-D arrays of small particles.

The Magnetic Force Microscopy (MFM) technique is demonstrated to provide quantitative information on not only micromagnetics but also on recording performance. A novel method is introduced for analyzing MFM images of recorded bit patterns to determine recording parameters such as signal and signal-to-noise ratio. The results are compared with those measured by a read head. Both signal and signal-to-noise ratio are found to be higher in the CoCrTaPt/CrMo medium than in CoCrTa/Cr medium for linear densities greater than 150 kfci. Recorded patterns can be observed in CoCrTaPt for linear densities up to 370 kfci while the patterns in CoCrTa start to deteriorate for densities higher than 250 kfci. Better high density performance of CoCrTaPt results from the finer structure of an isolated recorded transition which is attributed to reduced magnetostatic and exchange intergranular interactions. The direct overwrite patterns for CoCrTaPt exhibit narrower erase bands and less interactions between the old and new data; the overwrite at 232 kfci is 28dB.

Amorphous metallic [Fe.sub.78][Si.sub.9][B.sub.13] fibers, 50 [[micro]meter] in diameter, produced by the melt extraction method, have been studied in the as-quenched state and after furnace annealing at 455 [degrees] C and 480 [degrees] C for times between 0.5 min and 50 min. Measurements of the M-H loops and field dependence of Young's modulus have shown that they behave in a way very like that of amorphous wires. The minimum coercivity of 3 A/m is greater than that found in wires, and the minimum Young's modulus ([approximately]0.45 times the saturation value) is greater. It is suggested that the core-shell domain model applies in the as-quenched state and that stress relief followed by surface crystallization dominate the anisotropy.

In order to synthesize separately the residual amorphous phase present in rapidly quenched nanocrystalline FeSiCuNbB ribbons, powders of nominal composition [Fe.sub.92-x][Nb.sub.8][B.sub.x] with x = 19...45 as well as [Fe.sub.63][Nb.sub.9][B.sub.28] and [Fe.sub.55][Nb.sub.12][B.sub.33] were mechanically alloyed for amorphization and annealed at 540 [degrees] C for structural relaxation. The amorphous powder products show crystallization temperatures [T.sub.x1] and [T.sub.x2] increasing with B content from 600 to 750 [degrees] C and 750 to 950 [degrees] C, respectively. The Curie temperature and also room-temperature saturation polarization show maximum values of about 140 [degrees] C and 0.8 T at a B content of 25 at.%. Compared to that, the Curie temperature of the amorphous grain boundary phase of same composition in nanocrystalline FeSiCuNbB is by at least 100 [degrees] C higher, presumably caused by exchange-field penetration from the adjacent [Alpha]-FeSi nanocrystallites.

Samarium cobalt nanoparticles were prepared by ball milling under argon, both with and without a surfactant. X-ray diffraction indicated a single Sm[Co.sub.5] phase, with an average size of 25 nm from Debye-Scherrer analysis of the peak widths, but a broad size distribution based on TEM. SQUID magnetometry yielded the coercivity as a function of temperature between 4 and 300 K. Large coercivities ([H.sub.c] = 2.1 T at 10 K) were observed in the bare particles, but the values were significantly reduced ([H.sub.c] = 0.12 T at 5 K) for those coated with surfactant, indicating probable surface oxidation.

The magnetic properties and structures of Ni and NiFe nanocrystalline films prepared with the gas-deposition method (GDM) are investigated. From the results of STM and SEM, fine particles, approximately 10 nm in diameter, were seen in the films. Furthermore, aggregates several tens of nm in diameter, composed of the small particles, are also observed. The magnetization of the Ni nanocrystalline films is about 50 emu/g, or 90% of that of bulk Ni. Coercivity of the Ni nanocrystals ranged from 4 to 20 Oe. In the case of NiFe, the concentration of Fe is slightly increased as the evaporation temperature is increased.

Ferromagnetic chains consisting of metallic Fe spheres having 20-70 nm diameter have been fabricated by a reduction of ferrous chloride with potassium borohydride. The variations in particle size, boron content and crystallinity with synthesis conditions are investigated. The magnetic properties are examined as a function of annealing temperatures. The observed magnetic properties are correlated to particle size and crystallinity.

Magnetic properties of ultra-thin Fe(100) films are studied experimentally, with an emphasis on the temperature dependence of the magnetization and the influence of the substrate on magnetic properties. It is found that the nature and orientation of the substrate, here Au(100) and Pd(100), have significant effects on the character of the ferromagnetic phase transition, in particular the thermodynamic behavior near the Curie point is strongly dependent on the details of the system, in contrast to the case of bulk Fe. These results are consistent with predictions for the XY model with crystalline anisotropies.

[Fe.sub.x][Ge.sub.100-x] films with compositions in the range 50[less than or equal to]x[less than or equal to]82 at 300K were deposited by rf diode, sequential sputtering from elemental targets. All the films were amorphous at 300K indicating that the Fe concentration in the stable amorphous films was increased by more than 10 at. % over that obtained by vapor deposition. The sequentially sputtered Fe-Ge films exhibited a heteroamorphous morphology with nanoscale features that varied with composition. The variations in the 4[Pi][M.sub.S] and [T.sub.c] for the sputtered Fe rich films, agreed well with data extrapolated from measurements on Ge rich evaporated films. The improvement in the soft magnetic properties produced in these films by rotating magnetic field annealing (RFA) was shown to be correlated with changes in film morphology.

Co-Fe-Si-B films have been prepared using a roll coater and DC magnetron sputtering system onto a polyethylene terephthalate substrate. This thin film exhibited an excellent uniaxial anisotropy introduced by an asymmetric thermal shrinkage of the substrate. Reversal with a single large Barkhausen pulse has been observed in a thin film structure 1mm by 50mm by 0.65 [[micro]meter]. Closure domains have been clearly identified at the film ends. The threshold for the reversal is the coercive force. The reason for reversal with a single Barkhausen jump is that the long narrow film geometry has essentially zero demagnetizing field over most of the film. Once the walls start to move through the center portion of the film, there is nothing to stop them so the reversal proceeds with a single large Barkhausen pulse.

The systematic variations in the magnetic properties of as-deposited (by RF diode sputtering) and annealed [Co.sub.x][Fe.sub.100-x] (x=0, 15, 50, 67, 90, 100) alloy thin films were studied in this work. Maximum values of 4[Pi][M.sub.s] (21.3 kGauss) and [H.sub.c] (253 Oe) were observed in as-deposited films with, respectively, x=15 and x=50. Films with 0[less than or equal to]x[less than or equal to]15 had rotatable hysteresis loops with squareness S[approximately equal to]1. With increasing Co, S decreased and the films became isotropic. Large decreases in [H.sub.c] and resistivity, and large increases in 4[Pi][M.sub.s] were produced in films with x=50 and 67 by annealing in vacuum at 370 [degrees] C, in the presence of an in-planefield. The in-plane anisotropy of the annealed films had a complex biaxial symmetry. A similar biaxial anisotropy was observed in [Co.sub.90][Fe.sub.10] films deposited in an [approximately equal to]200 Oe planar field. This anisotropy was observed independent of whether the substrate was crystalline Si, glass or polyimide. Thus the biaxial anisotropy could not be ascribed to structural constraints at the film-substrate interface, but was probably induced in the film during deposition. The optimum binary CoFe alloy films for application at GHz frequencies require highly oriented uniaxial anisotropies. For reasons not fully understood, it was not possible to obtain well oriented as-deposited, or annealed, binary CoFe films with uniaxial anisotropy.

The effects of [Co.sub.79][Cr.sub.21] undercoats and nucleating layers on the coercive force, anisotropy field, and 5 MHz to 100 MHz complex permeability spectra of magnetically soft, [Ni.sub.81][Fe.sub.19] thin films rf sputtered onto glass substrates are investigated. While very thin layers of hcp oriented [Co.sub.79][Cr.sub.21] [approximately equal to] 5 nm, do not affect the coercive force of the NiFe layer, they do increase the measured anisotropy. Thicker CoCr layers increase both the coercive force and anisotropy field. The 5 nm layers of [Co.sub.79][Cr.sub.21] act to increase the magnitude of the [Mu][prime] spectra, [Mu] = [Mu][prime] - j[Mu][double prime], while decreasing the [Mu][double prime] spectra; thicker layers of CoCr reduce both [Mu][prime] and [Mu][double prime].

Ultrafine Gd particles in a Cu metallic matrix have been obtained by post-annealing of as-sputtered metastable [Gd.sub.x][Cu.sub.1-x] alloys at temperatures higher than 250 [degrees] C. The results of resistivity measurements show that the resistivities of as-sputtered metastable [Gd.sub.0.2][Cu.sub.0.8] and [Gd.sub.0.3][Cu.sub.0.7] alloys exhibit a resistivity minimum at low temperatures, an indication of the Kondo effect. In addition the temperature of the resistivity minimum rises with the increasing Gd content. Conversely, the resistivity of films after formation of Gd granules levels off at low temperatures. The magnetic results indicate that the metastable GdCu alloys are essentially a spin-glass at low temperature with the transition temperatures at around 3.5-5K. However, magnetization data at 80K shows that the as-sputtered samples contain some small Gd ferromagnetic clusters in the paramagnetic matrix. The magnetic particles of granular films begin to be thermally blocked at [T.sub.B] and become magnetically ordered below [T.sub.B]. Due to larger grain sizes, [T.sub.B] is much higher for x=0.3 than for 0.2. The variation of transport and magnetic properties for samples with different annealing processes are described in detail.

We have studied the structure and soft magnetic properties of Fe-ceramic([Si.sub.3][N.sub.4], [Al.sub.2][O.sub.3]) thin films fabricated by an rf magnetron sputtering apparatus using a composite target. The concentration of solute in the film increases linearly with the area fraction of ceramic pieces in the target. In the case of [Si.sub.3][N.sub.4], the concentration of O increases largely with the Ar pressure, especially at high Ar pressures of more than 20 mTorr. In [Al.sub.2][O.sub.3], the composition of Al and O exhibits a maximum at the Ar pressure of 20 mTorr. As the area fraction of the ceramic increases, the structure of the film changes from a crystalline phase to an amorphous phase. The electrical resistivity increases significantly with increasing area fraction of the ceramics. The saturation magnetization decreases inversely with the logarithm of the electrical resistivity. The gradient of the decrease in saturation magnetization against electrical resistivity is lower in the [Al.sub.2][O.sub.3] system than that in the [Si.sub.3][N.sub.4] system. The Ar pressure dependences of the electrical resistivity and the saturation magnetization are similar to that of the thin film composition. Fe-[Si.sub.3][N.sub.4] films exhibited a saturation magnetization of about 8 kG, a hard-axis coercivity of 0.2 Oe, an electrical resistivity of about 800 [Mu] [Omega]-cm and a permeability(100 MHz) of higher than 400.

The magnetostatic interaction between elements of a regular two.dimensional array of rectangular garnet pixels has been investigated. The up- and down switching fields of an individual pixels, have been measured magnetooptically. The switching characteristics of a given pixel depends on the state of the neighbors. In this work the effect of the magnetization state of the first 5 coordination shells on a central, test pixel was investigated experimentally and numerically. The interaction field, i.e. the demagnetizing/magnetizing effects, is calculated exactly and in the dipole approximation for 24 pixels surrounding the central pixel. A good agreement between experimental and numerical results has been obtained.

Thin films of [Nd.sub.2][Fe.sub.14]B ([approximately]30-60 nm) were grown with c-axis texture bY means of molecular beam epitaxy. A two-phase structure is observed in both the x-ray diffraction and the hysteresis loops, due to an interfacial reaction during the initial growth. Coercivities are 1-2 T at 20 K, and the anisotropy fields are bulk-like. Microstructural analysis by atomic and magnetic force microscopies reveal lateral grain sizes of [similar to]200 nm, which could explain the hard magnetic properties.

Rare-earth-transition-metal thin films are successfully grown by magnetron sputtering onto single-crystal MgO substrates with epitaxial W buffer layers. The use of epitaxial W buffer layers allows oriented single-phase films to be grown. Sm-Co films grown onto W(100), have strong in-plane anisotropy and coercivities exceeding 5 T at 5 K whereas Fe-Sm films have strong perpendicular anisotropy and are magnetically soft.

Soft magnetism in FeN-based films intimately depends on the lattice dilation caused by N incorporation. We suggest that the softest magnetic properties can be predicted in terms of critical lattice dilation. A detailed investigation of the structure constant in FeTaN films is presented and theoretically described. A comparison is made between Takahashi and Shimatsu's model as a function of the lattice dilation and Doyle and Finnegan's model with respect to the film stress. Finally, predictions are made for the behavior of FeSiN and FeAIN films.