GIANT MAGNETORESISTANCE IN AUFE ASSAYS - EVIDENCE FOR THE PROGRESSIVEUNBLOCKING OF SUPERPARAMAGNETIC PARTICLES

Measurements were performed of the magnetic-field dependence of the ma gnetization M(B) and the magnetoresistance MR(B) of a Au85Fe15 alloy. It was found that although MR(B) is proportional to the square of M(B) at higher temperatures (above 120 K), a term linear in M(B makes an i mportant contribution to MR(B al lower temperatures. These results are interpreted as evidence for the presence in the alloy of a range of s izes for the: Fe particles which become progressively unblocked (super paramagnetic) as the temperature increases. A calculation based on thi s interpretation yields quantitative agreement with both the M(B) and MR(BI data at all temperatures.