Magnetic phase transition in (Fe,Mn)65Ni35 alloys

Magnetization measurements on the Fe60Mn5Ni35 and Fe50Mn15Ni35 alloy samples were carried out in the temperature range 80 less than or equal to T less than or equal to 300 K and in magnetic fields up to 8 kOe. The Fe60Mn5Ni35 was found to order ferromagnetically with a Curie temperature, T-c, above 300 K. From the temperature dependence of the spontaneous magnetization, M-s, it was concluded that the magnetic behavior of Fe60Mn5Ni35 follows Wohlfarth theory of weak itinerant ferromagnet. The Fe50Mn15Ni35 sample exhibits a magnetic phase transition from ferromagnetism to paramagnetism at T-c = 242 K. The critical amplitudes and critical exponents (beta, gamma and delta) have been determined by using Arrott plots, Kouvel-Fisher method and scaling plots of the reduced magnetization and reduced magnetic field. The values of beta, gamma and delta are discussed and compared with the results obtained for various theoretical models and also with the experimentally determined values for related systems obtained by others. (C) 2000 Elsevier Science B.V. All rights reserved.