Low Field Simultaneous AC and DC Magnetization Measurements of Amorphous (Fe0.20Ni0.80)75P16B6Al3and (Fe0.68Mn0.32)75P16B6Al3

In a SQUID magnetometer we have simultaneously measured the a.c. susceptibility (6 Hz, 10 nT (0.1 mG) rms) and the d.c. magnetization at applied d.c. fields up to 0.5 mT (5 G) of the amorphous materials (Fe 0.20 Ni 0.80 ) 75 P 16 B 6 Al 3 and (Fe 0.68 Mn 0.32 ) 75 P 16 B 6 Al 3 . Both samples have an iron content slightly higher than the concentration at the multicritical point for the respective alloy system. When the temperature is increased, the samples are characterized by spin-glass (SG), ferromagnetic (FM) and paramagnetic (PM) behaviour. In both samples the FM-PM transition is well defined (Fe, Ni): 87 K; (Fe, Mn): 98 K, while the SG-FM transition is ambiguous. In the (Fe, Ni) sample a rather broad SG-FM transition appears at approx. 20 K in both a.c. and d.c. measurements. The d.c. thermoremanent curve (TRM) shows a minimum at the same temperature. The (Fe, Mn) sample shows a sharp decrease for decreasing temperature at 57 K in a.c. as well as d.c. measurements, suggesting the position of the SG-FM transition. The TRM curve shows a pronounced dip at the same temperature and typical viscosity effects are observed below this temperature.