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Hot-pressed [Nd.sub.13.5][Fe.sub.77][Si.sub.1][B.sub.8] alloy compacts with various grain sizes ranging from approximately 50 nm to 200 nm were prepared using melt-spun material. The compacts were then subjected to die-upsetting. The effect of grain size in the hot- pressed compact on the texture in die-upset magnet was investigated. The effect of die-upset temperature on the texture in die-upset magnet was also investigated. Texture in the die-upset [Nd.sub.13.5][Fe.sub.77][Si.sub.1][B.sub.8] alloy samples decreased with increasing the grain size in the hot-pressed compact before the die-upsetting. This dependence of texture on the initial grain size could be explained by the unique texture formation mechanism of a stress-induced preferential grain growth via dissolution and precipitation. Texture of the die-upset sample was also influenced by the die-upsetting temperature. The samples die-upset at 700[degrees]C and 900[degrees]C had poorer texture compared to the samples die-upset at the temperature range of 750[degrees]C-850[degrees]C. The poor texture in the sample die-upset at lower temperature of 700[degrees]C was attributed to the less dissolution of the unfavorable [Nd.sub.2][Fe.sub.14]B grains and low fluidity of the liquid Nd-rich grain boundary phase. The poor texture in the sample die-upset at higher temperature of 900[degrees]C was explained by the reduced elastic modulus and the excessive grain growth of the [Nd.sub.2][Fe.sub.14]B grains. Index Terms--Hard magnetic materials, magnetic materials, magnets, permanent magnets.

Electronic and thermodynamic properties of the ternary Dy[Ni.sub.4]Si compound, crystallizing in the hexagonal Ca[Cu.sub.5] structure (P6/mmm space group) were studied by X-ray photoelectron spectroscopy (XPS) and heat capacity measurements. Dy[Ni.sub.4]Si is ferromagnetic with magnetic moment 7.9 [micro]B/f.u. at 4.2 K (in H = 9 T) and Curie temperature [T.sub.C] = 11 K. The heat capacity measurements have shown that Dy[Ni.sub.4]Si is characterized by electronic heat capacity coefficient [gamma] = 72 mJ/mol K. Zero field heat capacity reveals a peak close to the magnetic ordering temperature, which gets suppressed in an applied field of 5 T. The valence band of the XPS spectra is determined mainly by the Ni(3d) and Dy(4f) contributions. The slight shift of peaks' positions towards the higher binding energy by about 0.3 eV in respect to the pure Dy is probably due to the different crystalline electric field for Dy in the Dy[Ni.sub.4]Si compound. Index Terms--Ferromagnetic materials, magnetic field effects, transition metal alloys, X-ray spectroscopy.

In this paper, we report on temperature effects associated with elastic electromagnetic forming by pulsed electromagnetic fields in inhomogeneous, linear, and lossy media. In a previous paper, we discussed the electromagnetic forces associated with these pulsed electromagnetic fields. Here, we calculate the temperature rise from the equation of heat flow in an isolated object to be deformed. The temperature rise is included in the elastodynamic problem to be solved for the presence of electromagnetic forces, and as a consequence the thermoelastic field can be obtained. As an example, we calculate the thermoelastic field in a hollow cylindrical object. Index Terms--Conducting magnetic materials, elastic field, electromagnetic forming, electromechanical forces, temperature rise, thermoelastic field.

This paper reapproaches the very classic problem of the analytic study of nonlinear diffusion of electromagnetic fields in conducting media. Significant contributions that appeared in the literature on this topic are cited in order to highlight the interest and the efforts provided by the scientific community on this topic as well as the aim and the main results of this work. The capabilities of two analytic procedures for estimating the energy losses in magnetic materials with hysteresis are shown and discussed. One formulation reduces the full nonlinear diffusion problem to a linear problem through an optimization procedure and is suited for thick cores. A second formulation approximates the magnetic field behavior by means of polynomials and provides good results for thin laminations. Energy losses are evaluated for magnetic materials with different B-H relations operating in wide frequency intervals. A scalar Preisach model, numerically treated, is used as a benchmark and, finally, calculations are compared with experimental data provided by other authors. Index Terms--Analytical technique, magnetic materials, nonlinear diffusion equation, thin lamination.

The thermal of property of magnetic materials at higher temperatures us examined and used in Active Magnetic Regenerative Refrigeration (AMRR) project. The results provide a deep insight into thermal properties of rare earth compounds and is useful for designing and development of the practical AMRR for hydrogen liquefaction.

A dual-axial anisotropy film which consists of two uniaxial sandwiches of [Co.sub.91] [Nb.sub.6] [Zr.sub.3]/Si[O.sub.2]/[Co.sub.91] [Nb.sub.6][Zr.sub.3] with their easy axes orthogonally oriented, was fabricated by RF-sputtering using a water-cooled, magnetic substrate holder, for application in a new type of submicron trackwidth thin film head. The thermal stability of the induced uniaxial anisotropy of the film was studied by heat treatment in a magnetic field and subsequent magnetic measurements. The magnetic properties of the films before and after rotational field annealing (RFA) were studied by their B-H loops and permeability spectrum along various directions in the film plane. It was found that the B-H loops of the as-deposited dual-axial film along either axis were the superposition of the easy axis and hard axis B-H loops of the two uniaxial sandwiches along that axis. The two uniaxial sandwiches appear to behave independently before RFA. In-plane isotropic B-It loops and isotropic permeability of 2640 at 10 MHz were obtained for the dual-axial films after RFA at 320 [degrees] C. The small [H.sub.[Kappa]] and the magneto-static interaction between the two sandwiches may be mainly responsible for the isotropic magnetic properties of the dual-axial film after RFA. Index Terms - CoNbZr, dual-axial anisotropy, isotropic permeability, rotational field annealing, submicron trackwidth, thin-film head.

The effect of substrate bias applied during the deposition of NiO on the properties of unshielded NiO/[Ni.sub.81][Fe.sub.19] and NiO/[Co.sub.87][Fe.sub.13] biased spin-valve sensors was investigated. The addition of substrate bias of -40 V increased the blocking temperature [T.sub.b] from 100-190 [degrees] C for NiO/NiFe biased spin valves, and from 70-190 [degrees] C for NiO/CoFe biased spin valves. The thermal stability upon anneal increased with substrate bias from 150-200 [degrees] C for NiO/NiFe biased spin-valve sensors, and from 200-280 [degrees] C for NiO/CoFe biased spin-valve sensors. At an operating temperature of 80 [degrees] C, sensor magnetoresistance decreases 15% from its room temperature value for NiO/CoFe sensors where NiO was deposited under -40 V bias. At this temperature, the sensor transfer curves are well linearized and Barkhausen noise free. NiO films prepared with varying substrate bias were examined by atomic force microscopy (AFM) and X-ray diffraction. Substrate bias decreases surface morphology and grain size of NiO, which probably contributes to the observed improvement of blocking temperature. Index Terms - Blocking temperature, exchange field, magnetoresistance, spin valve, substrate bias, surface morphology, thermal stability.

An experimental technique has been developed to accurately measure the time dependence of playback voltage due to the decay of recorded magnetization patterns. A 'calibration' procedure is utilized to minimize the effect of magnetoresistive head sensitivity variations. This technique is applied to a systematic study of the dependence of the signal decay on recording bit density and magnetic layer thickness in longitudinal thin film media. A Neel-Arrhenius type model is introduced to calculate the degradation of a square wave magnetization pattern subject to thermal agitation. Because the equivalent external field which reduces the energy barrier is the time and spatially varying magnetostatic field produced by magnetic transitions, an iterative procedure is utilized to obtain the time dependent magnetization. The model takes into account distributions of grain volume and anisotropy axis. The calculation results are compared with the experimental data and good agreement is obtained. Index Terms - Magnetic disk recording, stability.

This paper discusses several approximate analytic techniques for calculating power dissipation and forces in ferromagnetic fluids subjected to a spatially uniform but time varying magnetic field. This power dissipation results in a rising temperature in a ferrofluid sample. Several possible heating mechanisms in magnetic fluids have been investigated, including electromagnetic and hydrodynamic processes, and a simple method for prediction of power dissipation in a sample has been developed. Experimental results are given for an induction heating problem where it is shown that the power dissipation in a sample of ferrofluid cannot be explained by induction heating of the individual suspended particles. A simple viscous drag model is introduced which shows better agreement with measured power dissipation in the sample than an eddy current model for excitation frequencies under 1 MHz. Index Terms - Ferrofluid, induction heating, magnetic circuits, magnetic liquids, modeling.

Structural and magnetic properties of fine particles of magnetite are investigated with respect to the application for hyperthermia. Magnetic hysteresis losses are measured in dependence on the field amplitude for selected commercial powders and arc discussed in terms of grain size and structure of the particles. For ferromagnetic powders as well as for ferrofluids, results of heating experiments within organic gels in a magnetic high frequency field are reported. The heating effect depends strongly on the magnetic properties of the magnetite particles which may vary appreciably for different samples in dependence on the particle size and microstructure. In particular, the transition from ferromagnetic to superparamagnetic behavior causes changes of the loss mechanism, and accordingly, of the heating effect. The maximum attainable heating effect is discussed in terms of common theoretical models. Rise of temperature at the surface of a small heated sample as well as in its immediate neighborhood in the surrounding medium is measured in dependence on time and is compared with solutions of the corresponding heat conductivity problem. Conclusions with respect to clinical applications are given. Index Terms - Hysteresis, losses, relaxation, superparamagnetism.

A new scheme is proposed, which can treat electromagnetic field of the type-II superconductor under transient temperature field. In the analysis, one of the critical state models, the Bean model was employed to determine the current distribution in the superconductors and effect of magnetic flux flow was also taken into account. We chose both low and high Tc superconducting materials. Numerical results indicate that the flux flow strongly affects the stability against the quench in both materials. Index terms - High-temperature superconductors, Superconducting filaments/wires, Eddy currents

We have carried out a numerical analysis of the magnetic field on high-frequency induction heating. This analysis includes the dependence of various magnetic properties on temperature. The required characteristics are obtained experimentally. We compare the experimental results with the theoretical values obtained by approximations. Until now, the current density inside the exciting coil on this kind of problem has been assumed to be uniform, which is different from actual phenomena. We propose a new method which takes the inhomogeneous distribution of exciting current into account. In this analysis, the eddy current of the exciting coil is also taken into account.

We have studied the giant magnetoresistance (GMR) in granular Co- Ag, Co-Cu, and Fe-Ag systems, as well as in the metastable alloy state. The absolute values of the resistivity at zero field (Rho(sub 0)), the magnetic resistivity (Rho)(sub 0)), and GMR have been determined. The resistivity of an alloy is found to be significantly larger than that of a granular solid. As the composition (x) of Co or Fe is increased, Rho(sub m) shows a broad maximum at x = 20 to 30%. Among the three systems, Co-Ag has the smallest Rho(0), the largest Rho(m), hence the largest GMR. Both Rho(0) and Rho(sub m) at 5 K in all three systems show a similar dependence on the annealing temperature (T(sub A)). They decrease with increasing T(sub A), having the largest values in the as- deposited samples regardless of the sample being alloy or granular. Because Rho(0) and Rho(sub m) decrease with T(sub A) at different rates there may or may not be a peak in the GMR at certain value of T(sub A).

We report measurements on the thermal conductivity and thermoelectric power of granular Co20Ag80 solids annealed at various temperatures. Thermal conductivity is dominated by its electronic contribution and the Wiedemann-Franz law is found to be satisfied between 2K and 300K, which is mainly ascribed to dominant large-angle elastic scattering processes. The thermoelectric power is negative and is considerably reduced by the annealing process. Giant magnetothermal conductivity and giant magnetothermopower are found to be correlated with the giant magnetoresistance.

This paper deals with a new formulation of the Spectral Domain Technique (SDT) for the analysis of the general case of uniaxial/biaxial, electric/magnetic anisotropic multilayer planar structures. As an illustration of the capabilities of this formulation we apply it to the analysis of shielded CPW structures. The dispersive properties of the fundamental and higher order modes in various cases of electric/magnetic anisotropy as well as the induction electric and magnetic lines are calculated. Such results, and particularly the induction lines, may be used to predict the behaviour of the studied structure as well as to point out its sensitive geometrical and electrical parameters. Some general rules will be discussed which lead to a better understanding of the effect of anisotropy.

We have developed a method for isothermal calorimetry for the determination of the entropy change in magnetic materials. Heat absorbed and released by the sample at constant temperature is measured by means of Peltier cells, used in an active way to simultaneously measure the heat current and keep constant the sample temperature. In the paper we describe the method, the Peltier cell calibration and the test apparatus. The results obtained on a Gadolinium sample at room temperature under a magnetic field up to 0.9 T are discussed. The comparison with other methods demonstrates the validity of the proposed approach to fulfill the isothermal conditions ([DELTA]T[less than or equal to]5 mK) and to obtain a faster time response. Index Terms--Calorimetry, gadolinium, magnetocaloric, thermoelectric.

Soft magnetic composite (SMC) material is formed by surface-insulated iron powder particles, generating unique properties like magnetic and thermal isotropy, and very low eddy currents. This paper presents the design and analysis of a high-speed claw pole motor with an SMC stator core for reducing core losses and cost. The analyses of magnetic and thermal fields are conducted based on a comprehensive understanding of the property of SMC materials. The 3-D finite-element analysis (FEA) is performed for accurate parameter calculation, design optimization, and thermal calculation. Because of the importance of core loss in high-speed motors, rotational core loss model is employed, and the core losses are coupled directly into thermal calculation by keeping the same hexahedral mesh structure between magnetic field analysis and thermal analysis. Since the rotor modal analysis is very important to high-speed motors, the natural frequencies and mode of the rotor are studied. Index Terms--Core losses, finite-element field analysis, high-speed motors, modal analysis, soft magnetic composite (SMC) materials, thermal analysis.

A study of the magnetostructural phase transition and related magnetic entropy changes, [DELTA] [S.sub.M], in the vicinity of a first-order magnetostructural transition, in polycrystalline shape memory alloys [Ni.sub.2+x][Mn.sub.1-x] Ga (x = 0.16, 0.17, 0.18, 0.19, 0.20) have been done. Thermal expansion measurements reveal the gradual overlap of the first- and second-order phase transitions that results in the large magnetic entropy changes in the alloys. We observed a magnetic entropy change of [DELTA] [S.sub.M] = -66.2 J/[kg.sup.-1] * [K.sup.-1] between 350 K and 350.5 K in a field change of 5 T in [Ni.sub.2+x][Mn.sub.1-x] Ga for x = 0.19. Index Terms--Magnetic materials, magnetoelasticity.

A technique to sense the magnetic characteristics of the individual layers of a multi-layer structure is demonstrated. It detects the interaction between a thermal wave and the magnetization dependent thermal transport properties of the medium. A modulated laser beam is used to generate a thermal wave at the surface of a thin film sample and launch it into the medium. The amplitude and phase of the wave are modulated by the thermal properties of the medium as it propagates. Initial results for a AgNiFe magnetic thin film under a non-magnetic overlayer have successfully measured the magnetization dependent thermal conductivity. The measurements agree well with those obtained from the magnetization dependent resistivity.

Recently, several aftereffect models were proposed in which Preisach type hysteresis transducers are driven by stochastic inputs. Such inputs represent random thermal perturbations which are the source of the aftereffect phenomenon. According to these models, aftereffect is completely characterized by the magnetization history, the Preisach function and noise parameters. In this article, we present an identification of model parameters in which temperature-dependence is incorporated into the aftereffect model. The temperature variation of the noise parameters are investigated in order to predict the aftereffect decay coefficient. Comparison of numerical results with experimental ones observed in metal particle tape (MPT) magnetic recording media show a good agreement. As a result, based on the magnetization history, the Preisach function and noise parameters, it is shown that the model can be used to predict aftereffect characteristics of magnetic recording media of arbitrary magnetization history and temperature.

We present experiments on nanocrystalline materials where thermal activation gives rise to dynamic effects on hysteresis curves. A scheme of interpretation is presented and the typical activation volume is found to be about 100 nm. Index Terms - Thermal activation. Dynamic hysteresis loops. Nanocrystalline soft materials. Magnetic hardening.

A quasi-steady heat transfer model is introduced to study the mechanism of the variation of the heat flux between a slider and air bearing when the slider flies over an asperity without contact. The simulation results show that the heat flux is related to the air bearing spacing. When a slider flies over an asperity, its flying height fluctuates, which causes the air bearing spacing to fluctuate, and this in turn causes the heat flux between the slider and the air bearing to fluctuate. Corresponding to a decrease of the flying height, the heat flux out of the slider increases and vice versa. The variation of the heat flux causes a variation of the temperature of the Magnetoresistive (MR) transducer, and therefore a variation of the amplitude of the read-back signal. Index terms - Air bearing, hard drive, MR head, thermal asperity.

The use of anisotropic magnetoresistive (MR) heads at low flying height has led to the phenomenon of thermal asperities, read signal spikes caused by thermal effects when a slider impacts disk asperities. This paper presents a proposal for a wide trackwidth thermal asperity test head with a dual stripe sensor on a picoslider. While it turns out that a single stripe is sufficient to detect thermal asperities, a dual stripe sensor has the added advantage of being capable of reading magnetic index marks on the disk. This allows one to trace an asperity location after the disk has left the test stand. A thermal asperity signal waveform typically starts out with an undershoot. This effect is caused by greatly enhanced sensor cooling due to a reduction of the head to disk clearance when approaching the thermal asperity. Index Terms - Thermal asperity test head, picoslider, dual stripe sensor, thermal asperity signal waveform.

Thermally assisted reversal in noninteracting single domain particles is studied through the use of a micromagnetic model with a stochastic fluctuation field. The magnetization decay of these particles at high and low anisotropy fields is studied and compared to Arrhenius-Neel decay. Estimates of the attempt frequency are made by fitting to exponential decay. The attempt frequency is also examined while varying the applied field, the anisotropy field, and the temperature. Special attention is given to combinations of these variables which give a constant height of the energy barrier to reversal. It is shown that the attempt frequency can vary dramatically even for a constant height of the energy barrier. The basic scaling laws of the system are discussed, and the scaled attempt frequencies are plotted to test their universality. Index Terms-Arrhenius-Neel decay, attempt frequency, Langevin equation, scaling laws, thermal decay.

The effect of particle length on the magnetic viscosity and high speed switching characteristics were studied for four experimental metal particle (MP) tapes. The particle length varied from 80 nm to 340 nm with diameters [approximately]20 nm. The magnetic viscosity and activation volume were not senesitive to particle length. High speed switching measurements show only a moderate increase in the remanent coercivity at [10.sup.-8]s. Results are compared to new models of magnetization reversal in acicular particles.

The effect of the medium thickness of Co-Cr and Co-Cr-Pt perpendicular media on the signal-to-noise ratio (S/N) was investigated by using two different types of merged magnetoresistive (MR) heads. Two types of medium were employed in this measurement: Cr-rich [Co.sub.72][Cr.sub.28] and [([Co.sub.72][Cr.sub.28]).sub.78][Pt.sub.22] which have high-anisotropy field ([H.sub.k]). The write demagnetization increased when a shorter write gap was used. The high S/N value for the Cr-rich Co-Cr medium does not decrease even for a large medium thickness of 100-300 nm; however, the S/N of the Co-Cr-Pt medium decreases with increasing thickness. To obtain a high S/N value, two types of medium can be used. One is a Co-Cr-Pt medium whose thickness is less than 50 nm, and the other is a Cr-rich Co-Cr medium whose thickness is sufficient for thermal stability. The Cr-rich Co-Cr medium, which shows a high S/N for a large medium thickness of over 100 nm, will contribute to the thermal stability of magnetic bits at future high recording densities of 10 Gbits/[in.sup.2] and beyond. Index Terms - magnetoresistive head, medium thickness, perpendicular magnetic media, signal-to-noise ratio.

Output decay by thermal relaxation in perpendicular double-layered media is studied by numerical calculation and experiments. In addition some influences due to a single pole head are pointed out. We suggest that if these influences could be avoided, thermal relaxation in perpendicular magnetic recording would be much smaller than reported so far. High recording density and low noise is possible with relatively small particles, even at large film thickness in perpendicular magnetic recording. Index terms - Thermal relaxation, output decay, single-pole head, perpendicular magnetic recording.

Ultra-thin Co/Cr films were fabricated by RF diode sputtering. The highly exchange coupled Co grains were successfully isolated by post deposition processing. The microstructure was studied with TEM and a very small physical grain size was observed. The measurement of [Delta]M curves showed that the grain to grain interaction changed from positive to negative. Time dependent magnetic measurements showed significant thermal decay effects. It was also found that the use of CrMn underlayers instead of pure Cr further isolated the Co grains. Index Terms - Thermal stability, magnetic viscosity, superparamagnetism, magnetic recording media.

The effect of thermal fluctuation and particle-size dispersion on longitudinal and perpendicular magnetic recording media is investigated by computer simulation. In the case of longitudinal recording media the coercive force depends largely on the size of the particle rather than its distribution while it depends on both particle size and its distribution in the case of perpendicular recording media. Calculations performed to obtain read/write properties show that removal of particle-size dispersion results in 92% and 229% increase in the recording density in the case of longitudinal and perpendicular recording media, respectively, when particle size is 120[Angstrom]. Index Terms - grain size dispersion, magnetic recording, micromagnetic simulation, thermal fluctuation

The composition and temperature dependencies of uniaxial magnetocrystalline anisotropy constants [K.sub.u1] and [K.sub.u2] are investigated by torque magnetometry for (1010)-oriented [Co.sub.96-x] [C r.sub.x][Ta.sub.4] single crystal thin films (x = 8 - 19 at.%). The [K.sub.u1] and the [K.sub.u2] values of Co88Cr8Ta4 are determined at 290 K to be 2.2x[10.sup.6] and 5.9x[10.sup.5] erg/[cm.sup.3], respectively. The [K.sub.u1] and the [K.sub.u2] decrease to 6.9x[10.sup.5] and 5.3x[10.sup.4] erg/[cm.sup.3], respectively, with increasing Cr concentration from 8 to 19 at.%. When the temperature is increased from 290 to 450 K, [K.sub.u1] of [Co.sub.88][Cr.sub.8][Ta.sub.4] thin film decreases by 27 % to 1.6x[10.sup.6] erg/[cm.sup.3]. The temperature dependencies of [K.sub.u1] and [K.sub.u2] increase with increasing Cr content in Co-Cr-Ta films. The compositional and the temperature dependencies of [K.sub.u1] and [K.sub.u2] are related to the decrease in Curie temperature of Co-Cr-Ta material with increasing Cr concentration. Index terms - Co-Cr-Ta single crystal thin film, magnetocrystalline anisotropy, Curie temperature

The thermal stability of GdDyFeCo films with trilayer structure has been studied by annealing in vacuum up to 300 [degrees] C. In GdDyFeCo films sputtered on glass, the coercivity is reduced after annealing, which is thought to be due to a structural relaxation caused by annealing. The saturation magnetization tends to increase upon annealing, in particular for rare-earth rich composition because of the increase of effective magnetic moment, making the compensation temperature (Tcomp) shift higher. The films with Tcomp between room temperature and 100 [degrees] C show superior thermal stability, because their magnetic properties, especially Tcomp, change little after annealing. Overwrite repetition tests using magnetic field modulation recording also indicate that the disks with the Tcomp between room temperature and 100 [degrees] C have superior overwrite durability. Small adjustments of the GdDy content seem to be effective in improving the thermal stability of GdDyFeCo films. The best Tcomp of the GdDyFeCo films is between room temperature and 100 [degrees] C, and the optimum Dy:Gd ratio is between 45/55 and 70/30.

Thermomagnetic recording behavior was investigated in a bilayer which was composed of a TM-rich NdTbDyFeCo layer and a high-Tc RE-rich DyFeCo ultrathin layer. The magnetic field sensitivity of the bilayer was investigated by a magnetic field modulation method at a low field of 4kA/m. Carrier-to-noise-ratio depends sensitively on the thickness of the ultrathin layer and reaches its maximum value at approximately 2.5nm. Using a polarized light microscope it was observed that the domain formation process makes a transition from nucleation-dominated (ND) to wall-motion-dominated (WMD) as the thickness increases, and during the transition the highest magnetic field sensitivity was achieved. We explained those results with a model in which the domain formation started in WMD and ended in ND.

We have studied the magnetic properties of the nanocrystalline Fe79Ta10C11 films with different crystallographical characteristics. The soft magnetic properties are not related to the Fe characteristics but closely related to the TaC characteristics, such as the lattice parameter and grain size. The film composed of fine TaC grain with small lattice parameter has excellent soft magnetic characteristics at room temperature and its magnetic properties little change with temperature. On the contrary, the film composed of large TaC grain with large lattice parameter has large coercive force and magnetostriction at room temperature and shows the anomalous magnetic behavior at high temperature; the coercive force at 300 degrees C becomes 10 times larger than that at room temperature. This phenomenon is most likely caused by the disappearance of the intergranular ferromagnetic coupling.

To determine the temperature dependence of the magnetization of three commercial high energy product permanent magnet materials under conditions approximating those in a permanent magnet circuit, a method was devised whereby measurements were made at values of Mu(sub L) = B/Mu(sub 0)H that remained constant as the temperature was varied. All the values of Mu(sub L) used were on the same spherical sample for any given material. The values of micron(sub L) ranged from zero to ten thousand to mimic almost any circumstance likely to be encountered in most real permanent magnet circuits. The method of measurement is described and an example of the material selection procedure for an actual magnetic circuit is given.

The principal phase resulting from the reaction of Sm2Fe17 with zinc is a solution of Sm in Gamma-Fe-Zn. At the maximum Sm content this cubic phase with a = 0.8984 nm has an approximate composition of (at.%) 5 Sm, 42 Fe, 53 Zn and has no permanent magnetic moment between 4.2 and 600 K. The phase equilibria of the low-Sm alloys in Sm-Fe-Zn show that isostructural Sm2Fe17 and Sm2Zn17 are not miscible and that, because of the pervasiveness of equilibria with Alpha-Fe, it will be difficult to eliminate Alpha-Fe completely from Zn-bonded magnets.

The magnetic properties of a series of highly aligned Nd(Fe,Mo)12 and Nd(Fe,Co,Mo)12 samples were measured before and after nitriding. The samples were synthesized as approximately 2 micrometer thick sputtered film samples with the crystallite c-axes aligned perpendicular to the film surface. Part of the Mo in the NdFe11Mo based ThMn12 phase was replaced with Co to enhance the available flux density. The saturation flux density for H perpendicular to the film surface was 12.9 kG without Co replacement, and was 15.5 kG with 50% of the Mo replaced with Co. The films were uniaxial before and after nitriding. Upon nitriding the anisotropy field at room temperature increased from 5 to 130 kOe. For a NdFe11MoNx sample with some excess Nd the static energy product for measurements perpendicular to the film surface was 30.2 MGOe at 293 K, and 43.5 MGOe at 10 K. For a NdFe11Co0.5Mo0.5Nx the energy product at 293 K was 46.3 MGOe. For this Co containing sample the room temperature HA was estimated to be 150 kOe. At 10 K the 4 Pi M(sub s) was 17.0 kG, the iHc was 24.0 kOe, and the energy product was 59.6 MGOe.

The addition of 2 at% Ta or 1 at% Ti into a (Nd,Dy)-(Fe,Co)-B alloy is very effective in improving room temperature coercivity and thermal stability. The Ta containing alloy showed 30 % higher coercivity value than that of Ta-free alloy at temperatures higher than 100 degrees C. Both Ta and Ti alloying greatly reduced the high temperature reversible losses at temperatures of up to 225 degrees C. They are thus potential in high temperature applications.

Neutron-diffraction and Mossbauer effect studies of Y2Fe14-xSixB, where x is 0.28, 0.67, and 1.87, show that silicon preferentially occupies the 4c site in the R2Fe14B structure. If the breaking of short iron-iron bonds is the mechanism for the increase in the Curie temperature of R2Fe14-xSixB, then the bonds most responsible for the in6crease are those between iron atoms on the 16k(sub 2) and 4c sites.

The effects of the melt temperature on the magnetic properties of the nanocrystalline Fe73.5Cu1Nb3(Si0.6B0.4)22.5 alloy were previously investigated and it was found that the soft magnetic properties improve with increased melt temperature. In this paper, in order to examine the melt temperature effects of alloys with varying degree of glass forming ability, we investigate the magnetic properties of nanocrystalline Fe73.5Cu1Nb3(SixB1-x)22.5 (x=0.4-0.8) alloys. It is found that for all the alloys, except for x=0.8, the soft magnetic properties of the ribbons quenched at the high melt temperature are better than those of the ribbon fabricated at the low melt temperature, in agreement with the previous observation, but the magnitude of improvement in the magnetic properties with increased melt temperature decreases with decreasing glass-forming ability. The present result emphasizes that the glass-forming ability of an alloy should be taken into account in considering the melt temperature effects.

The coercivity and phase transformations of Fe73.5Cu1Nb3Si22.5-xBx nanocrystalline alloys as a function of temperature (540 and 620 degrees C), annealing times (up to 240 min) and composition (x=6 and 9) have been investigated by means of magnetic measurements, Mossbauer spectroscopy and X-ray diffractometry. Nanocrystalline microstructure after annealing at 540 degrees C gives rise to a softening of the material, while after annealing at 620 degrees C for short times a magnetic hardening is observed before a significant increase in size of the Alpha-Fe(Si) grains and the detection of a secondary Fe2B phase. The initial stages of Fe2B precipitation seem to be responsible for this magnetic hardening.

Amorphous alloys of composition Fe86Zr7Cu1B6 have been prepared and annealed in the temperature range from 570 to 950 K, obtaining several degrees of nanocrystallization. Magnetic and Mossbauer measurements show the different phases that appear in the samples after the heating, and their percentage, depending on the annealing temperature. The Curie temperature of the amorphous phase is shown to remain almost unchanged during the crystallization. Mossbauer spectroscopy however, reveals subtle changes in the structure.

We report here on the effect of annealing temperatures on the spin wave excitations for the nanocrystalline Fe88Zr7B4Cu1 alloy, observed from the low temperature magnetization curve and the spectroscopic splitting g factor. The thermomagnetization curve at low temperature is found to obey the Bloch law, M(sub s)(T) = M(sub s)(0)(1 - BT(super 3/2) - CT(super 5/2). From these experimental results, spin wave stiffness constants within the annealing condition were calculated. In addition, effective permeability, coercive force, saturation magnetization (B10), magnetostriction and magnetic anisotropy of the annealed alloys have been studied systematically.

The ac susceptibility of metallic iron particles in a matrix of the zeolite NaX has been studied as a function of temperature and frequency. Information about the particle size distribution has been obtained from a computational analysis of the experimental data. The resulting sizes agree with previous determinations on the same sample based on other techniques.

A study of the low temperature magnetic behavior of a metastable fcc-FeCu solid solution obtained by mechanical alloying as well as of the subsequent annealed product is carried out. The metastable solid solution is ferromagnetic and it has a temperature dependence of the magnetization which follows a T(super 3/2) law. During annealing the metastable phase decomposes into Cu and Fe phases. It has been found that the low temperature magnetization of this subsequent mixture decreases with respect to that of the fcc solid solution. Moreover the Mossbauer spectrum obtained shows a paramagnetic Fe phase with the same relative resonant area than the percentage of the decrease in magnetization. These results suggest that after the annealing process, not all the iron is found in the stable and ferromagnetic bcc or Alpha phase, but a noticeable proportion probably remains as fcc particles of Gamma -Fe.

Heat treated Cu80Co15Fe5 melt-spun ribbons were analyzed for their structural and magnetoresistance (MR) properties. Magnetoresistance values were found to be a maximum for the sample annealed at 500 degrees C. Structural characterization using X-ray diffraction and absorption measurements, together with transmission electron microscopy, show this sample to have two precipitate phases within a Cu-rich fcc matrix; a Co-rich fcc phase and a CoFe bcc phase. Heat treatments at higher temperatures brought about a decrease in MR. Dark field TEM images illustrate the clustering of the precipitate particles concurrent with the decrease in MR suggesting that a clustering mechanism may contribute to the MR effect in these materials.

Thermally activated domain wall dynamics in ultrathin Au/Co/Au films with perpendicular anisotropy have been studied at different tempera-tures. Barkhausen volumes and activation energies of the samples are derived. The origin of the coercive field is briefly discussed.

We report here on the effect of annealing temperatures on the spin wave excitations for the nanocrystalline Fe68.5Co5Nb3Cu1Si13.5B9 alloy, observed from the low temperature magnetization curves and the spectroscopic splitting g factors. The temperature dependence of magnetization was measured with a vibrating sample magnetometer and spectroscopic splitting g - values were estimated from ferromagnetic resonance (FMR) experiments. Coercive force, initial permeability and AC power loss of the annealed alloys have been studied systematically. The thermo-magnetization curve is found to obey the Bloch law, MS(T) = MS(0)(1 - BT3/2 - CT5/2). From these experimental results, spin wave stiffness constants and the range of the exchange interaction within the annealing condition were calculated.

Measurements of the structure, magnetic properties, and magnetostriction were made on arc-melted polycrystalline [([Tb.sub.0.7][Dy.sub.0.3]).sub.0.7][Pr.sub.0.3] [([Fe.sub.1-x][Co.sub.x].sub.1.85] (0 [is less than or equal to] x [is less than or equal to] 0.6) alloys by X-ray diffraction, initial susceptibility, vibrating sample magnetometry, and standard strain gauge techniques. The measurements showed that the matrix of [([Tb.sub.0.7][Dy.sub.0.3]).sub.0.7] [Pr.sub.0.3][(Fe.sub.1-x][Co.sub.x]).sub.1.85] predominantly consists of the Mg[Cu.sub.2]-type cubic Laves phase, with a small amount of Pu[Ni.sub.3]-type and rare-earth rich phases. The amount of (Tb, Dy, Pr)[(Fe, Co).sub.2] in [([Tb.sub.0.7][Dy.sub.0.3]).sub.0.7] [Pr.sub.0.3][([Fe.sub.1-x][Co.sub.x]).sub.1.85] increases with increasing Co concentration and becomes almost the only phase present when x [is greater than or equal to] 0.4. The lattice parameter decreases approximately linearly with increasing x from 0.7357 nm when x = 0 to 0.7300 nm when x = 0.6. The Curie temperature increases with increasing x from 640 K when x = 0 to 677 K when x = 0.3, and then decreases to 572 K when x = 0.6. The saturation magnetization [M.sub.s] exhibits a minimum near x = 0.3. The polycrystalline magnetostriction of [([Tb.sub.0.7][Dy.sub.0.3]).sub.0.7][Pr.sub.0.3] [([Fe.sub.1-x][Co.sub.x]).sub.1.85] decreases monotonically with increasing x. There is no evidence of an anomalously large [Lambda].sub.100] value as is the case for other R[([Fe.sub.1-x][Co.sub.x]).sub.2] compounds.