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The effects of spacer layer (SrTi[O.sub.3]) thickness on the magnetic and electrical properties of [La.sub.0.7][Sr.sub.0.3]Mn[O.sub.3]/SrTi[O.sub.3] superlattices has been studied by fabricating a series of multilayers on SrTi[O.sub.3] (100) substrates by pulsed laser deposition. High quality of the films was ensured by X-ray diffraction and transmission electron microscopy. All studied films are ferromagnetic below a transition temperature [T.sub.C]. The [T.sub.C] as well as saturation magnetization [M.sub.S] depend on the thickness of SrTi[O.sub.3]. However, these dependences are nonmonotonic. The electrical resistivity is metallic-like below 300 K. The magnetoresistance measured at 20 K has been found to depend on the SrTi[O.sub.3] thickness and correlates with the magnetic measurements. The results are discussed in terms of surface corrugation due to epitaxial strain, surface dead-layer concept, and interlayer coupling. Index Terms--Magnetic properties, magnetoresistance, superlattices.

At low temperatures melt-spun and subsequently annealed ribbons with the nominal composition [Dy.sub.x][Cu.sub.100-x] (x < 20) show a remarkable magnetoresistance ratio which is negative and isotropic. This effect is caused by the cubic Dy[Cu.sub.5] phase with the Au[Be.sub.5]-type structure. Below a critical temperature [T.sub.m] [approximately equal to] 7K this phase is metamagnetic. Between [T.sub.m] and [T.sub.c] [approximately equal to] 14.5K it shows a spontaneous magnetization i.e. it is ferromagnetic. The hexagonal Dy[Cu.sub.7] phase (Tb[Cu.sub.7]-type structure) is ferromagnetic with a Curie temperature of about 18K. This 1:7 phase as well as the lamellar Cu/Dy[Cu.sub.5] microstructure caused by the eutectoid decomposition of Dy[Cu.sub.7] do not result in a large magnetoresistance of the ribbons.

Giant magnetoresistance (GMR) has been observed in magnetically optimized AlNiCo5 and FeCrCo bulk alloys with amplitudes sizes as much as 3% at 300K and 5% at 10K. In contrast, homogenized FeCrCo samples show the anisotropic magnetoresistance. The field dependence of the GMR amplitude cannot be scaled by a simple function of magnetization due to a strong field dependence beyond saturation.

The magnetization processes in fine grained [Sm.sub.2][Fe.sub.17][N.sub.3] permanent magnets were studied with high resolution Kerr microscopy and measurements of the magnetization curves. Different susceptibilities after thermal and dc-demagnetization were observed for HDDR processed samples but not for long milled material. The differences for the HDDR material are interpreted considering cooperative magnetization phenomena ('interaction domains') that produce changes in the degree of frustration between the magnetization directions of neighbouring grains.

The hard magnetic properties of Nd[Fe.sub.12-x][Mo.sub.x][N.sub.0.9] with low Mo concentration (x = 1.25 and 1.5) have been studied. The coercivity varies with the ball milling time and reaches a maximum at about 800 minutes. Coercivity values [[Mu].sub.oJ][H.sub.c] of 0.64 T and 0.55 T have been achieved for nitrides with x = 1.25 and 1.5, respectively. The oxygen content of ball milled nitrides is less than 1 wt%. Metal bonding of Nd[Fe.sub.12-x][Mo.sub.x][N.sub.0.9] with Zn has less effect on coercivity than for [Sm.sub.2][Fe.sub.17][N.sub.y].

[Sm.sub.2][Fe.sub.17] carbides were prepared by arc-melting and gas-solid reaction (GSR). Zn-bonding was investigated as a means of developing coercivity on these carbides. Positive results were found by Zn-bonding carbides prepared by GSR where coercivities up to 0.9 T could be achieved after a proper heat-treatment. The [Alpha]-Fe originated due to disproportionation seems to be one primary hindrance for achieving coercivity values as high as for Zn-bonded nitrides. The effect of heat treatment conditions and Zn-content on the development of coercivity in [Sm.sub.2][Fe.sub.17] carbides is discussed and compared to results on nitrides.

At temperatures below 8.2 K large spontaneous jumps in the demagnetization curve of [Sm.sub.2][(Co,Cu,Fe,Zr).sub.17] magnets with high coercivity were detected. For different samples no correlations concerning the onset, the depth or the number of jumps could be observed. Systematic investigations showed the following results: i) The emergence and the number of jumps depend on the temperature, the field sweeping rate and the sample dimensions. ii) The onset of jumps is shifted to smaller applied fields with decreasing temperature. iii) The cooling conditions have a strong influence. These results have definitely shown that the observed polarization jumps are due to thermal instabilities because of the small heat capacity and poor thermal conductivity in agreement with a local heating model.

A least mean square procedure was used to fit five types of trial texture functions, each of them containing one fitting parameter, to demagnetization curves of Zn-bonded [Sm.sub.2][Fe.sub.17][N.sub.x] samples with varying degree of easy-axis alignment as well as Zn-bonded [Sm.sub.2][Fe.sub.17][C.sub.x]. The demagnetization curves were measured in the first quadrant of polarization-field plane, parallel and perpendicularly to the texture axis. The temperature dependence (above room temperature) of the intrinsic magnetic properties [K.sub.1], [K.sub.2], [J.sub.3] was determined for both materials. The sensitivity of the calculated anisotropy constants to the degree of easy-axis alignment turns out to be the best criterion to find out the correct texture function which can be described by a Gaussian density in the case of our Zn-bonded [Sm.sub.2][Fe.sub.17][N.sub.x].

The magnetic aftereffect of textured Zn-bonded [Sm.sub.2][Fe.sub.17][N.sub.2.9] was investigated using the extraction method for fixed external magnetic fields. A simple fitting procedure was developed in order to determine effectively the viscosity S and the correct type of irreversible susceptibility [[Chi].sub.irr]. There is no proportionality in the polarization dependence of S and [[Chi].sub.irr], resulting in a strong polarization dependence of the viscosity coefficient [S.sub.v]. The variation of the activation volume v with temperature, polarization and magnetic field is explained by a nonhomogeneous distribution of intrinsic properties, e.g. anisotropy constants, due to a nonhomogeneous degree of nitrogenation.

The substitution of elements M (M = Nb, V, Ti, Co) for Fe in Sm2Fe17Ny was investigated regarding its structural and magnetic properties. Zn-bonding as well as milling of Sm2(Fe1-xMx)17Ny was studied as a means of improving the properties of their corresponding permanent magnets. Co-substitution improves the temperature dependence of remanence, while V-containing magnets show a better shape of the demagnetization curve. Additional milling of nitrides enhances the coercivity, due to pinning of domain walls or to single domain particle behaviour. Zn bonding of very fine Sm2Fe17Ny powders, followed by heat treatment, e.g. 425 degrees C for 100 min., leads to an overall decrease of the permanent-magnet properties caused by the formation of Alpha-Fe.

After homogenization and subsequent nitrogenation melt-spun Sm2Fe17Nx shows high values of coercivity up to 2T. The coercivity was further increased to 2.9T by applying the Zn-bonding technique. Densities up to 6.7 g/cm cube could be achieved by Hot Isostatic Pressing (HIP). After HIP, however, the Zn-bonded samples show a deterioration in the shape of the demagnetization curves, which is due to the formation of Alpha-Fe as indicated by X-ray diffractometry.

The effect of annealing on coercivity JHc of sintered Nd-Fe-B is contradictorily discussed in literature. JHc depends on (i) annealing temperature T(sub A), (ii) annealing time, (iii) cooling rate, and (iv) details of the chemical composition. In the case of (Nd,Dy15(Fe,Co,Mo,Al)77B8 a decrease of JHc is observed for T(sub A) is greater than or equal to 450 degrees C. Passing a strong minimum at T(sub A) = 575 degrees C and a maximum at T(sub A) approximately equal to 800 degrees C, JHc approaches its post- sintering value at higher annealing temperatures. Above the minimum, JHc varies practically reversibly if T(sub A) is increased or decreased. The ratio of coercivities measured after annealing at 750 degrees C and 575 degrees C increases with increasing measuring temperature and is more than 5 above 150 degrees C. Analysing the behaviour of JHc by JHc = c HA - N) micron(sub o) to the -1)J(sub s) we found c = 0.43 for T(sub A) = 750 degrees C and c = 0.29 for T(sub A) = 575 degrees C, but N(sub e) = 1.4 is independent of T(sub A).

At temperatures below 200 K the demagnetization curves Zn-bonded Sm2Fe17Nx magnets show a dip indicating different types of ferromagnetic particles in the material. The coercivity decreases more rapidly with increasing temperature than the anisotropy field. The shape of demagnetization curves and the coercivity can be improved by sieving the milled powder. The internal magnetization processes are a combination of nucleation of easily movable domain walls and single-domain-particle processes.

Melt-spun [Fe.sub.10][Cu.sub.90] shows a negative magnetoresistance with a nearly linear dependence on external field. The microstructure has Fe-atoms on fcc-sites, corresponding to CuFe solid solution, and in bcc [Alpha]-Fe precipitates. Magnetic data indicate the presence of magnetic couplings between magnetic clusters. It is argued that both microstructures, corresponding to the two locations of Fe, yield a mechanism for magnetoresistance. The resistivity in zero field shows a minimum at a temperature above the magnetic freezing or ordering temperature determined as the peak of ac--susceptibility. Glassy dynamics is seen from a creep of the resistivity after cooling below the freezing temperature. A simple micromagnetic model is applied to describe the increase of magnetoresistance with the amount of precipitated [Alpha]-Fe. Index Terms--Fine Particles, Giant Magnetoresistance, Spin Glasses, FeCu.