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.