MAGNETIC-RELAXATION OF NANOWIRES - BEYOND THE NEEL-BROWN ACTIVATION PROCESS

Magnetic relaxation in Ni nanowires was measured both on single nanowi res and on an array of about 10(6) nanowires. The logarithmic relaxati on rate S = dM/dln(t) deduced from after-effect experiments is present ed as a function of both the applied field and the temperature. The fi eld dependence S(H) is very similar to the distribution of the switchi ng fields of the nanowires in the array, whereas the field dependence of the relaxation time of one single nanowire is linear in the time wi ndow of the experiment. The temperature dependence S(T) of arrays decr eases with increasing temperature. The measurement on the macroscopic array is used to infer the thermal behavior of the relaxation time of single nanowires. This temperature dependence is in conflict viith the Neel-Brown activation of magnetic monodomains.