Critical behaviour of Ho_2Fe_(17-x)Mn_x-magnetisation and M?ssbauer spectroscopy

摘要

The magnetic properties of Ho_2Fe_(17-x)Mn_x compounds (x = 0-2) of ferromagnetic ordering temperatures up to TC ~344 K have been investigated by DC magnetization and M?ssbauer effect measurements. The nature of the magnetic phase transitions and the critical behaviour around TC has been investigated by analysis of the magnetisation data and the critical exponents β, γ and δ determined. The critical exponents are found to be similar to the theoretical values of the mean-field model for which β = 0. 5 and γ = 1. 0, indicating the existence of a long-range ferromagnetic interactions. The isothermal entropy changes ΔS around TC have been determined as a function of temperature in different magnetic fields.