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For the first time, both the magnetoelectronic properties and the magnetic domain structure of a magnetic tunnel junction (MTJ) have been characterized simultaneously. In situ tunneling magnetoresistanee measurements for a spin-dependent tunnel junction were directly compared to magnetic domain behavior imaged using magnetic force microscopy (MFM) under the same applied fields, allowing for detailed investigation of electronic behavior relative to magnetic behavior. From the results, it was found that the resistance in the hysteretic field range (less than the coercivity of Hc = 800 A/m or 10 Oe) corresponded with the complex magnetic domain behavior observed in the MFM images and qualitatively matched micromagnetically modeled junctions. Index Terms--Domain structures, magnetic force microscopy (MFM), magnetoresistance, spin-dependent transport.

The effect of impurities on the magnetoelastic properties of Gd(sub 5)Si(sub 2.09)Ge(sub 1.91) system is reported through the measurement of thermal expansion. The results show that the impurities (mainly C, O, N, and F) in the Gd starting material alters the strain and Curie temperature of Gd(sub x)(Si(sub x)Ge(sub 1-x)) alloys.

[Gd.sub.5] ([Si.sub.2][Ge.sub.2]) and related compounds with similar (nearly equal Si-to-Ge ratio) composition exhibit large magnetoresponsive properties including a giant magnetocaloric effect, colossal magnetostriction, and giant magnetoresistance near a structural-magnetic phase transition that occurs close to ambient temperature [1]. Magnetic force microscopy (MFM) and vibrating sample magnetometry (VSM) measurements on single-crystal samples of these materials indicate that the easy magnetization axis is the b-axis of the orthorhombic magnetic phase--perpendicular to the slabs. In fact, the MFM image of a surface perpendicular to the b-axis is quite similar to domain patterns perpendicular to the easy axis of Co and other highly anisotropic magnetic materials. Therefore, it appears that [Gd.sub.5] [([Si.sub.x][Ge.sub.1-x]).sub.4] may require modeling similar to other multilayers and superlattices of rare-earth metals with one or more nonmagnetic constituents that exhibit long-range magnetic order across nonmagnetic layers. Many of the important phenomena of these Gd compounds could be explained by the interaction of localized Gd magnetic moments across the covalent bonding between atomic slabs, adapting models already suggested for other similar materials [2]. Index Terms--Magnetic force microscopy (MFM), magnetic materials, magnetic measurements, rare earths.