The paramagnetic-ferromagnetic transition in reentrant spin-glasses-a magnetoresistance study in ultra-low magnetic fields

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Abstract
The longitudinal magnetoresistance has been measured in the spin-glass and reentrant spin-glass states of Au-14 at.%Fe and amorphous (Fe1-xNix)77Si10B13 alloys by a new technique which involves applied fields of less than two gauss. The measurements have concentrated on the paramagnetic-ferromagnetic transition where in both crystalline and amorphous systems a curious negative magnetoresistance has been found over a small temperature range, which rapidly changes sign as the ferromagnetic state becomes established with decrease of temperature. From measurements of the field dependence of the magnetoresistance near the Curie temperature, the negative contribution, as well as the positive contribution, is found to continue to develop into the ferromagnetic state. The model used by Beck (1985), modified with the addition of a pin-glass type background matrix, is proposed from the study for the ferromagnetic state of these alloys.