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Giant magnetoresistance (GMR) in spin valves is due to spin-dependent scattering occurring at ferromagnet/normal metal (F/N) interfaces and/or in the ferromagnetic layers. In a spin valve with a typical F/N/F structure where the spin scattering asymmetry factor ([alpha]) of both F/N interfaces is the same (more or less than 1), the GMR is expected to be positive. If [alpha] is greater than one at one F/N interface and less than one at the other F/N interface, however, the GMR is expected to be negative. Here, we show that the F1/Cu/SAF/Cu/F2/IrMn dual spin valve structure exhibits negative GMR, where F1 and F2 are CoFe and SAF = CoFe/Ru t/CoFe, due to both opposite electron spin scattering asymmetry factor at the CoFe/Ru/CoFe interfaces as well as the electrical separation of the overall structure into two GMR spin valves connected in parallel. A GMR of 6% is observed in the structure without the Ru spacer layer, insertion of a 0.6 nm thick Ru in the SAF results in a negative GMR ratio of -3%, which becomes positive again at the Ru thickness of 0.8 nm, the oscillation from positive to negative MR is consistent with interlayer exchange coupling period across the Ru spacer. Index Terms--Dual spin valve, negative GMR, synthetic antiferromagnet.

A method is described for the fabrication of magnetic force microscopy tips via localized electrodeposition and focused ion beam milling departing from commercial tapping mode tips. Very high aspect ratios and interacting magnetic moments are possible without altering significantly the tapping resonant frequency of the cantilever. These tips can achieve high magnetic resolution at room temperature and open atmosphere. They can also be fabricated into any shape, with applications for ferromagnetic resonance measurements and nano-imprinting. Index Terms--Electrodeposition, focused ion beam milling, magnetic force microscopy (MFM), tip fabrication.

We report on cylindrical permanent-magnet structures that exploit the image effect in a surrounding circular soft-iron sheath. We present the theory for a general multipole ring, where the polarization direction [alpha] = (n + 1)[psi], n is a positive or negative integer, and [psi] is the angular coordinate. For the uniformly magnetized case n = -1, a long cylindrical ring produces no field in its bore, and the field outside the cylinder is that of a linear dipole. When surrounded by the sheath, the field becomes uniform in the bore and zero outside the cylinder. Higher multipole fields can similarly be transformed from outward fields to inward fields by using the sheath. The field can be varied continuously by moving the sheath. We describe a small variable-field device using a Nd-Fe-B cylinder that produces a flux density of 0-400 mT. Index Terms--Halbach cylinders, magnetic image effects, magnetic shielding, permanent-magnet flux sources.

The gas phase interstitial modification of rare-earth intermetallics is studied. Net reaction energies for nitrogen in Sm2Fe17 and Nd(Fe11Ti) are U0 = - 57 kJ/mole and U0 = - 51 kJ/mole, respectively. The equilibrium nitrogen concentration is calculated as function of temperature and gas pressure using a simple lattice gas model. For nitrogen in Sm2Fe17, refined diffusion parameters D0(N) = 1.02 mm2/s and Ea(N) = 133 kJ/mole, determined by thermopiezic analysis of the initial stage of nitrogen absorption, are used to calculate nitrogen profiles and the time dependence of the mean nitrogen content during nitrogenation. Similiar values are obtained for nitrogen in Nd(Fe11Ti), whereas the activation energies for hydrogen in Sm2Fe17 and Nd(Fe11Ti) are 31 kJ/mole and 45 kJ/mole, respectively. The elastic stress and strain profiles during nitrogenation are calculated. Important results are a large uniaxial strain near the surface of non-uniformly nitrided particles, and core expansion even in the absence of any nitrogen there. Curie temperature and K1 profiles are calculated and suggestions are made regarding the influence of stress on coercivity and disproportionation of the material.

Magnetic tunnel junctions (MTJs) with amorphous CoFeB and [Co.sub.2]MnSi electrodes were fabricated and examined. In the case of [[[Co.sub.90][Fe.sub.10]].sub.100-x], the x = 32% boron addition reduces the magnetization by 30% compared to [Co.sub.90][Fe.sub.10], yet the reduction of the tunnel magnetoresistance (TMR) is over 95 %. On the contrary, in the case of [Co.sub.(100-x-y)][Mn.sub.x][Si.sub.y], although net magnetization is very small at room temperature, the TMR can be as large as 7%. The character of each metalloid (boron and silicon) could be responsible for the peculiar behavior to each system. Index Terms--Amorphous, MTJ, spin-dependent tunneling.

A novel bath for electrodepositing FePt films was developed and films were electrodeposited on copper substrates with thickness up to 0.45 [micro]m. The magnetic and structural properties of the films were measured. The films developed 0.3.T coercivity after annealing at 400 [degrees]C and formed the L[1.sub.0] FePt phase. Films are shiny and smooth. Morphology was found to be affected by the annealing process. Index Terms--Electrodeposition, films, L[1.sub.0] FePt, magnetization.

The application of a magnetic field unexpectedly alters the rest potential of ferromagnetic electrodes in paramagnetic solutions of their salts. Anodic shifts of up to 60 mV in a field of 1 tesla were observed for 1 M iron electrodes in iron nitrate solution. The magnitude of the shift depends on magnetic field strength and orientation and it varies with the anion used. The shift is smaller for cobalt and nickel (~2 mV) than for iron. The effect is attributed to modifications in the rate of mass transport under the influence of the magnetic field gradient force. Index Terms--Eiectrode, ferromagnetic, field gradient force, magnetic field, magnetoelectrochemistry, rest potential.

In this paper, [Sm.sub.z][Zr.sub.y] [([Co.sub.1-x][Fe.sub.x]).sub.100-y-z] (nominal composition) powders, where 13 [less than or equal to] z [less than or equal to] 15, 0 [less than or equal to] y [less than or equal to] 5, and 0 [less than or equal to] zx [less than or equal to] 0.5, were prepared by mechanical alloying and annealed using an optimized procedure. As-milled powders were amorphous, or showed some small [alpha]-Fe crystallites, depending on Fe composition. Initially, powders with y = 0 were prepared with a view to optimize the Fe content, and it was found that x = 0.1 was the best Fe content for all Sm compositions. Samples without Zr showed a mixture of [Th.sub.2][Ni.sub.17], and [Th.sub.2][Zn.sub.17] structure types, as well as Sm[Co.sub.5] and [[mu].sub.0][H.sub.c] was high as 1.6 T. Powders were then made varying x and y, and keeping z = 0.1. These samples also showed a mixture of [Sm.sub.2][Co.sub.17], phases along with Sm[Co.sub.5], dependent on Zr content. Room-temperature coercivities greater than 2.0 T were observed. Enhanced remanence ([[sigma].sub.r]/[[sigma].sub.s] [greater than or equal to] 0.65) is achieved in all compositions, indicating intergrain exchange coupling among the fine grains. Index Terms--Hard magnetic materials, mechanical alloying, permanent magnets, rare earth alloys.

The effect of Fe, Cu, Zr, and Ti substitution on magnetic properties of SmCo 1:7 magnets at temperatures up to 500[degrees]C were studied. As-milled amorphous Sm[(Co,Fe,Cu,Ti-Zr).sub.7] magnets crystallized in the Tb[Cu.sub.7]-type structure after annealing at 750[degrees]C for 2 h. A room-temperature intrinsic coercivity of around 2.5 T is obtained for compositions Sm[Co.sub.6.4] [Zr.sub.0.2] [Ti.sub.0.4] and Sm[Co.sub.6.4][Fe.sub.0.1][Zr.sub.0.1][Ti.sub.0.4]. The high coercivity of the bail-milled Sm[Co.sub.7-x][Ti.sub.x] magnets is attributed to the strong pinning of the wails of the 'interaction domains' by the network of grain boundaries between the nanocrystalline grains. The virgin curve of the bail-milled samples is suggestive of strong domain wall pinning. Index Terms--Coercivity, Curie temperature, magnetization, X-ray diffraction.

Electron-doped double perovskite compounds ([Sr.sub.2-x][La.sub.x])FeMo[O.sub.6] (x = 0.0, 0.5, 0.7) were synthesized by combustion synthesis using Oxalic acid dihydrazide as fuel. There is an increase in Curie temperature ([T.sub.C]) with La substitution up to a value of 172[degrees]C for ([Sr.sub.1.3][La.sub.0.7])FeMo[O.sub.6]. The compound ([Sr.sub.1.5][La.sub.0.5])FeMo[O.sub.6] with increased [T.sub.C] compared to the undoped sample, exhibits a intergrain magnetoresistance of about 3% in a field of 0.1 T. The presence of magnetoresistance in La-doped samples prepared by combustion synthesis is due to the increased number of intergrain tunnel barriers. Index Terms--Curie temperature, magnetoresistance, resistivity, X-ray diffraction.

The grain boundary phase/material found to be present in two-phase mechanically alloyed nanocomposites of [Sm.sub.2][Fe.sub.17][N.sub.3]/Fe and [Nd.sub.2][Fe.sub.14]B/Fe was characterized using Mossbauer spectroscopy and magnetization measurements. The fraction of iron in this third component is typically 10-15% in [Sm.sub.2][Fe.sub.17][N.sub.3]/Fe and 4-5% in [Nd.sub.2][Fe.sub.14]B/Fe nanocomposites. The influence of the grain size of the nanocomposite and the grain boundary material on the susceptibility was studied and the results are discussed in terms of the model of Wang and Mills.

The crystal-field parameters [A.sub.20] and [A.sub.40] were determined from the magnetocrystalline anisotropy constants [K.sub.1] and [K.sub.2] in a linear approximation for [Sm.sub.2][Fe.sub.17][Z.sub.x] (Z = N, C) compounds. For the materials investigated, the values of [K.sub.1] and [K.sub.2] in a temperature range from 4.2 - 533 K have been obtained by a fit of demagnetization curves. The parameters [A.sub.n0] are calculated in two ways: i) from the [K.sub.i] at zero temperature and ii) from the temperature dependence of the [K.sub.i]. Both methods give equivalent results. The value [Mathematical Expression Omitted] has been obtained which corresponds to an inverse THOMAS-FERMI screening length q [approximately equal to] 2.3 [[Angstrom].sup.-1] calculated within the framework of the screened charge model.

Fine cobalt and silver powders have been ball-milled to yield a granular solid of composition [Co.sub.30][Ag.sub.70] in the form of coarse powder. The material is an intimate mixture of grains of fcc Co in a silver matrix. The cobalt is in the single-domain size range, and the samples exhibit coercivity (0.07 T at 296 K) and unusual thermomagnetic effects, including field-induced unidirectional anisotropy. There is a large, isotropic negative magnetoresistance, which exceeds 10% at 4.2 K.

Size effects in two-phase Boolean magnets composed of an aligned hard phase and a soft phase with high magnetization are investigated. In 'overcritical' magnets, where the size of the soft regions is larger than the Blochwall width [[Delta].sub.h] of the hard phase, the energy product is reduced compared to the corresponding 'undercritical' magnets with small soft regions, where theoretical energy products as high as 1 MJ/[m.sup.3] have been predicted. Nevertheless, the theoretical energy product only gradually drops with increasing size of the soft regions, and it may still exceed the theoretical energy product 516 kJ/[m.sup.3] of [Nd.sub.2][Fe.sub.14]B.

Non-equilibrium nitrogenation of transition-metal rich rare-earth intermetallics can be used to increase the nitrogen content beyond its equilibrium concentration. For example, nitrogenation of [Sm.sub.2][Fe.sub.17] using ammonia yields volume expansions up to 8.3 vol %, which correspond to a composition [Sm.sub.2][Fe.sub.17][N.sub.x] with x [approximately equal to] 4. This effect is related to catalytic action at the metal surface where ammonia is decomposed into nitrogen and hydrogen, with nitrogen absorption on a site where it is weakly bound, as an intermediate step. For overloaded [Sm.sub.2][Fe.sub.17][N.sub.x] with x > 3 the net reaction energy [U.sub.o] = 5 [+ or -] 10 kJ/mole indicates a nearly temperature-independent occupation of the non-9e sites.

Exchange hardning of nanostructured two-phase systems composed of an aligned hard phase and a soft phase with high magnetization is investigated using a micromagnetic approach which accounts for interactions between the soft regions. For Sm2Fe17N3 (2.5 nm)/Fe65Co35(9nm) multilayers an energy product as high as 1 MJ/m cube (120 MGOe) is predicted, with a rare-earth content of only 5wt%. Giant energy products may also be achieved in suitable cellular and disordered structures.

Presents a study that assessed cylindrical permanent-magnet structures that exploit the image effect in a surrounding circular soft-iron sheath. Introduction of a theory of sheathed infinite length cylindrical multipole magnet structures using the idea of magnetic images in the surrounding iron; Observations on the changes in multipole field when surrounded by a sheath; Description of the construction and performance of a small dipole ring magnet.