We present a point-contact spectroscopy study on the spin glass CuMn (1%) using a mechanically controllable break junction. Here we can continuously vary the contact size d from 1 μm down to the atomic regime and thereby investigate size effects in spin-spin (spin glass) and spin-conduction electron (Kondo) interactions. Differential resistance dV/dI as a function of bias voltage V has been determined for the above alloy at various d and in different applied magnetic fields up to 10 T. A characteristic spin glass behavior is found for dV/dI vs V at large d which mimics the bulk resistivity ρ(T). A magnetic field enhances the spin glass minimum at zero bias at the cost of the Kondo peak at higher bias. As d is reduced the dV/dI behavior becomes more Kondo-like; i.e., a more pronounced negative slope emerges. Finally for d values of a few angstroms a pure Kondo response is found. Our results can be interpreted with a model whereby ${\mathit{T}}_{\mathit{K}}$ strongly increases as d decreases, thus suppressing the spin glass features. © 1996 The American Physical Society.

• Received 22 December 1995

DOI:https://doi.org/10.1103/PhysRevB.53.15106