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Fe top layers with a thickness [t.sub.Fe] between 1 and 15 nm were deposited on textured FePt(001)/Pt(001)/Cr(002) layers to study the associated exchange coupling effect and their switching behaviors. The deposition of a Fe layer does not change the crystalline structure of the FePt layer. Microstructural analysis reveals that the Fe(200) texture is formed epitaxially on the FePt(001) surface. When [t.sub.Fe] = 1 nm, the remanent coercivity ([H.sub.cr]) remains the same as that without a Fe top layer. The lack of reversible magnetization reveals that the Fe layer is thinner than the critical thickness; the strong coupling force throughout the whole Fe layer facilitates the cooperatively magnetic rotation of Fe and FePt layers. Significant exchange spring was observed in the sample with [t.sub.Fe] = 3 and 5 nm, reducing Her by 14% and 43% (the maximum reduction), respectively. The results are consistent with the theoretical prediction. As [t.sub.Fe] was increased up to 8 and 12 nm, the exchange spring effect disappeared. Although the two films exhibited similarly reduced Her values of about 1.5 kOe, the reduction of Her is caused by the tilt of the magnetic moments rather than the exchange spring. This incline of the moments is caused by the weakened exchange coupling and the complex domain structure. The magnetic reversal was further examined by measuring the variation in longitudinal and transverse magnetizations during magnetic field sweeping. The results suggest that at [t.sub.Fe] = 1 and 3 nm, the reversal occurs cooperatively in a single direction. As [t.sub.Fe] is increased to 5 and 8 nm, the moments switch randomly, in a manner that may be related to the increase in the density of the domain wall, observed by MFM. This work demonstrates the feasibility of reducing coercivity through exchange-spring mechanism and provides information on detailed magnetic reversal mechanism in perpendicular exchange coupled FePt. Index Terms--Exchange coupling, FePt thin films, magnetic reversal behaviors, perpendicular recording.

The present paper deals with the study of hybrid-bonded magnets consisting of strontium ferrite powder and Nd-Fe-B rapid solidified flakes with epoxy resin. A three-component constrained mixture design, employing ten runs for the experiment, was used. The magnetic properties such as remanence ([B.sub.r]), coercivity ([H.sub.c]) and energy product [(BH).sub.max] were used as the response. The results were modeled in the form of mathematical equation to predict the response as a function of Nd-Fe-B, strontium ferrite powders and polymer content. Full cubic model equation was found to be adequate to predict the magnetic properties. The predicted results from the obtained mathematical equation were compared with the experimentally measured values. Index Terms--Hard ferrite, hybrid-bonded magnets, mixture design, Nd-Fe-B.

This paper explores [(FePt).sub.100-x-][(MgO).sub.x] films with x = 0 - 6.13, deposited on an MgO underlayer at elevated temperatures by sputtering. The films exhibit good (001) texture and perpendicular anisotropy. The effects of adding MgO are summarized as follows: 1) the (001) alignment is degraded, increasing the in-plane squareness ratio ([S.sub./]/); 2) a linear dilution of magnetization at an applied field of 6 Tesla was observed; and 3) a critical MgO content of 1 vol. % was found for chemical ordering, microstructure, and anisotropic field ([H.sub.k]). Below this critical content, the ordering of FePt and its microstructure remain similar to those with x = 0 but with a markedly enhanced [H.sub.k]. As x exceeded 1 vol. %, the ordering declined linearly with increasing MgO content. Additionally, a well-defined granular structure was formed and [H.sub.k] was reduced. The decrease in the lattice constant along the c-axis as x increased between 0 and 1 vol. % reveals that the enhancement of [H.sub.k] is related to the relaxation of the residual strain/stress that originates from the ordering transformation of FePt. Adding the proper amount of MgO improved the magnetic properties of (001)-textured FePt. Index Terms--[L1.sub.0] FePt, MgO addition, MgO underlayer, perpendicular anisotropy.

Percolated perpendicular FePt-MgO films with a [([Fe.sub.48] [Pt.sub.52])100.sub.-x]-[(MgO).sub.x]/Pt(001)/Cr(002) structure were prepared by conventional dc magnetron sputtering (x = 0 - 6.13). Magnetic measurements demonstrate that the coercivity of the magnetic film drastically increases from 169 to 285 kA/m as the MgO content is increased from 0 to 0.15 vol.%. However, the grain sizes of the FePt phase do not significantly varying upon doping with MgO. MgO does not appear at the grain boundaries of the FePt phase, but is present as crystalline dots that are uniformly precipitated in the FePt matrix. The MFM images revealed that the domain structure transformed from extending to isolate when the MgO dots precipitated into the FePt grains. Consequently, the MgO dots serve as pinning sites of the domain wall and enhance perpendicular coercivity. Percolated perpendicular magnetic recording is thus regarded as a solution to the problem of thermal instability in ultrasmall grains. Index Terms--Coercive force, FePt alloy, percolated meida, perpendicular magnetic recording, precipitation.

A Cr underlayer was doped with 10 at. % Ru to enlarge the Cr lattice and promote the Co(11.0) formation of the CoCrPtTaB magnetic layer by in-plane tensile stress at a recording layer/underlayer interface. The texture, grain size and magnetic characteristics of CoCrPtTaB/Cr(Ru) were examined as well. The CrRu(002) underlayer exhibit markedly enhanced Co(11.0) orientation, increasing coercivity and preferential alignment of the c-axis. The grain size and grain size distribution of the recording layer decreased as the CoCrPtTaB magnetic layer grew epitaxially on the CrRu underlayer. The grain size of the recording layer was reduced from 11.2 nm with a pure Cr underlayer to 5.4 nm with a CrRu underlayer. The latter is the smallest grain size yet reported for CoCr-based alloy recording media. Index Terms--Chromium alloys, cobalt alloys, epitaxial growth, magnetic recording.

Single-layer polyerystalline [Fe.sub.52][Pt.sub.48] alloy thin films were deposited on preheated natural-oxidized (100) silicon wafer b y conventional sputtering method at room temperature. The as-deposited films are soft fee FePt phase. After suitable temperature annealing and furnace cooling, the as-deposited films are transformed from disordered soft fcc FePt phase into ordered fct L[1.sub.0] FePt phase. The ordering temperature of L[1.sub.0] FePt phase could be reduced to about 350[degrees]C by preheating substrate to 300[degrees]C followed by furnace cooling treatment. The grain size of FePt was found to decrease as the ordering temperature of L[1.sub.0] FePt phase was reduced. After annealing at 350[degrees]C for 1 h, the in-plane coercivity ([H.sub.c']) of the 100-nm [Fe.sub.52][Pt.sub.48] alloy thin film is about 6 k0e, and the average grain size is about 6 nm. Index Terms--Grain size, order-disorder transformations, sputtering.

From our previous studies, it has been found that the Fe-Pb-O granular films which have been adequately annealed exhibit an enhanced tunneling magnetoresistance effect (TMR). The TMR effect is about 10% at room temperature, which can be claimed as the maximum value ever detected so far. In this report the TMR effect of Fe-Pb-O granular films from different annealing time have been investigated. The Mossbauer spectrometer was used to collect the information of Fe magnetic microstructure. It has been found that the tunneling barrier from the magnetic compound formed between a-[Fe.sup.2][O.sub.3] and PbO plays an important role in obtaining large TMR effect. And the non-magnetic Fe-Pb-O compounds which exist on the surface of iron granules as a thin layer and grow with annealing time seem to decrease TMR effect.

This study develops a direct scheme that is based on the magnetization curve of magnetic nanoparticles in the medium-field region above the blocking temperature to extract information on the size of particles and the uniformity thereof. The magnetization curve was fitted with a computer software that was developed in-house and based on the linear addition of the Langevin functions that correspond to particles of different sizes. Numerically generated curves demonstrate that a standard deviation in volume of 10% generates a variation in magnetization of approximately 1%. The fitting program was tested on a series of generated curves for magnetic nanoparticles with various average volumes and standard deviations, yielding results with errors of around 3%. The program was also justified using the data obtained from several published articles, and the results herein were found to agree closely with those in the articles. Magnetite nanoparticles were monodispersed in a polymer matrix and magnetic measurements were made. The obtained results were compared with transmission electron microscopy observations to further validate the developed scheme. [ABSTRACT FROM AUTHOR]

Gd impurities, incorporated into metastable antiferromagnetic Cr-rich alloys, exhibit minimal effect on the antiferromagnetism of the alloys. Changes in spin-flip (TF) and Neel (TN) temperatures between 10 and 300K reveal a broad resistivity minimum, occurring at low and high temperatures depending on Gd concentration in the alloys.

A large value of magnetoresistance ratio has been observed in granular Fe-Pb-O solids. The large MR value is associated with the appearance of magnetic Pb ferrite encapsulated on the surface of iron granules. Spin-dependent tunneling picture can qualitatively describe the enhancement of magnetoresistance ratio. Calculated results based on the spin filter effect of the Pb-ferrite layer are reasonably in agreement with the experimental data of TMR enhancement in Fe-Pb-O solids. Index Terms--Tunneling magnetoresistance, spin-dependent, granular film, spin polarization.