Effect of thermal and field cycling on the magnetoresistivity of CuMn spin glass

We report measurements of the magnetoresistivity of CuMn 4.7% and CuMn 1.35% after a number of different magnetic and thermal cycles in the spin glass state. First, our CuMn 4.7% sample was cooled in zero field down to 1.2 K and then submitted for a short time to some maximum field H_max. Immediately after H_max was removed the low field (LF) Δρ versus H curve was plotted. Similar low H measurements were then repeated for increasing strengths of H_max. Two marked shoulders take place at H_max≊15 kG and become very sharp for H_max≳30 kG. In order to see whether or not the LF loop is reproducible we measured the same loop about 10 times and found a marked narrowing of the cycle of about 40%. This result cannot be described by a rigid anisotropy axis for which we rather expect a widening of the loop. Examples showing how the form of the LF magnetoresistance loop changes when the temperature is varied in H=0 are presented.