EXCHANGE-CORRELATION LENGTH AND MAGNETORESISTANCE IN FE-CU AND FE-CU-NI MELT-SPUN RIBBONS

The magnetic properties of Fe30Cu70 melt-spun ribbons are reported for the first time. In the as-cast state, the microstructure consists of b.c.c.-Fe grains immersed in a Cu-rich matrix. However, the addition o f a small percentage of Ni gives rise to the appearance of new Cu-Fe-N i phases. Under suitable thermal treatments, the microstructure of bot h alloys evolves towards a complete phase segregation in b.c.c-Fe and f.c.c.-Cu immiscibles phases. The temperature dependence of the magnet ic properties is analysed and related to the microstructural changes p roduced during the thermal treatments. Remarkable magnetoresistance ef fects have been observed in both as-cast alloys, with maximum values o f the order of 6% at low measuring temperatures.