Mn 5 Si 3 C x films exhibit antiferromagnetic or ferromagnetic behavior depending on the carbon doping level x. We report a detailed electronic-transport study of films prepared with different x. All films exhibit metallic behavior of the temperature-dependent resistivity ͑T͒ with a logarithmic increase towards low temperatures attributed to the structural disorder and the accompanied scattering of conduction electrons by two-level systems. Below 1 K, the Kondo-type behavior ͑T͒ϳ−ln T shows a crossover to Fermi-liquid behavior ϳ −T 2 independent of the type of magnetic order. The magnetoelectronic properties such as Hall effect and magnetoresistance show clear differences characteristic for the different magnetically ordered phases, i.e., antiferromagnetic vs ferromagnetic.

The electrical conductance G of mechanical break-junctions fabricated from the rare-earth metal dysprosium has been investigated at 4.2 K where Dy is in the ferromagnetic state. In addition to the usual variation of the conductance while breaking the wire mechanically, the conductance can be changed reproducibly by variation of the magnetic field H, due to the large magnetostriction of Dy. For a number of contacts, we observe discrete changes in G(H) in the range of several G(0) = 2e(2)/h. The behavior of G(H) and its angular dependence can be quantitatively understood by taking into account the magnetostrictive properties of Dy. This realization of a magnetostrictive few-atom switch demonstrates the possibility of reproducibly tuning the conductance of magnetic nanocontacts by a magnetic field.

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The role of a magnetic field present during formation of a ferromagnetic nanocontact—established by mechanically pulling a thin dysprosium wire—is investigated. We demonstrate that the shape of the nanocontact depends on the strength and direction of the magnetic field applied during plastic deformation of the contact. The different contact shapes obtained after cycles of tensile or compressive stress are attributed to the rearrangement of magnetic domains during formation of the nanocontact by magnetoelastic coupling.