Dimensionality crossover in CuMn spin‐glass films

The dynamic properties of Cu (13.5 at. % Mn) spin‐glass films of various thicknesses have been investigated in a superconducting quantum‐interference device (SQUID) magnetometer. The films are produced in a dc‐sputtering system and fabricated in the form of multilayer samples. Utilizing zero‐field‐cooled magnetization and ac‐susceptibility measurements, the time‐dependent susceptibility has been probed over eight decades in time (10⁻⁴–10⁴ s). Drastic changes of the dynamics are found upon varying the film thickness from 10⁴ to 20 Å. The most significant feature is a crossover from a behavior typical for bulk spin glasses for the 10⁴‐Å film, with a finite critical temperature and a critical slowing down that can be accurately described by a conventional power‐law divergence, to a slowing down for the very thin films that obeys a generalized Arrhenius law with a zero‐temperature critical point. Thus, these measurements indicate a crossover from three‐ to two‐dimensional spin‐glass dynamics when one spatial dimension is gradually diminished to a finite size.