Dedicated t o Prof. Dr. A. SEEGER on the occasion of his 60th birthdayThe magnetic phase transition of amorphous FeNi-base alloys and disordered crystalline FeNi alloys is investigated, and the methods for a determination of the asymptotic critical exponents and the effective exponents are discussed critically. Two general results are obtained: 1) For the asymptotic exponents no significant deviations from the 3d-Heisenberg exponents are found.2) For the effective susceptibility exponent y( T) the characteristic non-monotonic temperature dependence is observed as predicted by the correlated molecular field theory.Der magnetische Phasenubergang amorpher und ungeordnet kristalliner FeNi-Legierungen wird untersucht, und die Methoden zur Bestimmung der asymptotisch kritischen Exponenten und der effektiven Exponenten werden kritisch diskutiert. Es ergeben sich zwei allgemeine Resultate: 1) Fur die asymptotischen Exponenten werden keine signifikanten Abweichungen von den 3d-Heisenberg-Exponenten gefunden. 2) E s wird die charakteristische nichtmonotone Temperaturabhingigkeit des effektiven Suszeptibilitatsexponenten y( T) beobachtet, die von der korrelierten Molekularfeldtheorie vorausgesagt wird.
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