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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.

Using high performance soluble imide polymer as a binder, it was possible to accomplish a substantial mechanical strength in iron particle cores molded under uniaxial compacting pressure which was much lower than that was commonly applied by others in the past. The directional ordering of oblate spheroidal iron particles occurred despite the low compacting pressure resulting in strong anisotropy in the magnetic properties and mechanical strength in the fabricated cores. The low molding pressure, however, resulted in a low density of core which, in turn, caused the low permeability.

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.

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.

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.

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.

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.

The magnetic properties, phases transformations and microstructural evolution of [Nd.sub.9.5][Fe.sub.85.1-x][B.sub.5+x](x=0, 1, 3 and 4) alloy ribbons have been investigated. Excellent magnetic properties with a Br=11.7 kG, iHc=6.6 kOe, (BH)max=18.7 MGOe and Br=11.4 kG, iHc=6.3 kOe, (BH)max=19 MGOe, can be achieved in the alloys with x=0 and 1, respectively, simply from direct quenching. For alloy ribbons with higher boron content (x=3 and 4), the magnetic properties degrade and are lower than that of the former even after subsequent annealing. From x-ray diffraction, TEM and magnetic analysis, the degradation of magnetic properties was found to result from the formation of [Fe.sub.3]B phase inside [Nd.sub.2][Fe.sub.14]B and [Alpha]-Fe phases and to grain coarsening leading to the reduction of the exchange coupling effect between [Nd.sub.2][Fe.sub.14]B and [Alpha]-Fe or [Fe.sub.3]B phases.

Nd-Fe-B/Fe/Nd-Fe-B trilayers with individual layer thicknesses between 10 and 100 nm have been grown by sputter deposition. The aim of our study is to investigate remanence enhancement due to exchange coupling between the soft- and hardmagnetic layers as a function of the Fe-interlayer thickness d. It is shown that for decreasing d the remanence of the trilayer system is significantly increased due to exchange coupling. The coercivity of the trilayer is also increased for d < 40 nm which can be explained with a higher nucleation field for magnetization reversal.

An externally applied magnetic field during heat treating the [Nd.sub.2][Fe.sub.14]B/[Fe.sub.3]B based spring magnet was found to enhance the exchange coupling between the hard and soft magnetic grains. More than 30% increase in [M.sub.r]/[M.sub.s] values for melt-spun [Nd.sub.4][Fe.sub.73.5][Co.sub.3]([Hf.sub.1-x][Ga.sub.x])[B.sub.18.5] (x=0. 0.5, 1) alloys was resulted from a uniform distribution of [Fe.sub.3]B, a-Fe as well as [Nd.sub.2][Fe.sub.14]B, and also from the reduced grain size of those phases by 20%. The externally applied magnetic field induced the uniform distribution of fine grains. The present study also showed that there is an optimum grain size exhibiting a high coercivity (22 nm for the [Nd.sub.4][Fe.sub.73.5][Co.sub.3][Hf.sub.1-x][Ga.sub.x][B.sub.18.5] alloys).

Four samples of [Nd.sub.2][Fe.sub.17-x][M.sub.x][C.sub.y] (where M = Al, Ga, Ti, V) were synthesized using rf induction melting and C was introduced from the melt. Structural studies were then carried out using neutron diffraction. All samples were confirmed to have the [Th.sub.2][Zn.sub.17]-type rhombohedral structure with expanded unit cell volumes. However, the volume effect, as well as the site preference of the substitutionai atoms (M) is different among these samples and is different compared to their uncarbided counterparts. The C atoms were found to reside in the 9e site for all samples. The observed Curie temperature is higher for samples with higher C concentrations.

Neutron diffraction has been used to study a series of [Y.sub.2][Fe.sub.14-x][Al.sub.x]B solid solutions with x=0.65, 0.92, 1.30, 1.53, and 1.93. Aluminum atoms are found to occupy the j2 and c sites. The Al site affinity appears to be determined by the steric effect (j2) or crystal environment (c). The c lattice parameter increases as the aluminum content x increases, while the a lattice parameter decreases as the aluminum content x increases. The unit cell volume increases as the aluminum content x increases, at a rate around 3 [[Angstrom].sup.3] per Al atom per formula unit, much lower than observed in the Al substituted 2:17 compound. The average Fe site moment decreases as the aluminum content x increases due to the reduction of the Fe content.

The HDDR-behaviour of a series of as-cast alloys given by the general formula [Nd.sub.16][Fe.sub.76.-x][B.sub.8][Zr.sub.x] (0