SIZE-DEPENDENCE STUDY OF THE SPIN-GLASS CUMN (1-PERCENT)

We present a point-contact spectroscopy study on the spin glass CuMn ( 1%) using a mechanically controllable break junction. Here we can cont inuously vary the contact size d from 1 mu m down to the atomic regime and thereby investigate size effects in spin-spin (spin glass) and sp in-conduction electron (Kondo) interactions. Differential resistance d V/dI as a function of bias voltage V has been determined for the above allow 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 lar ge d which mimics the bulk resistivity rho(T). A magnetic field enhanc es the spin glass minimum at zero bias at the cost of the Kondo peak a t higher bias. As d is reduced the dV/dI behavior becomes more Kondo-l ike; i.e., a more pronounced negative slope emerges. Finally for d val ues of a few angstroms a pure Kondo response is found. Our results can be interpreted with a model whereby T-K strongly increases as d decre ases, thus suppressing the spin glass features.