Determination of the Transition Temperature of a Weak Ferromagnetic Thin Film by Means of an Evolution of the Method Based on the Arrott Plots

The ferromagnetic transition temperature Tc of a weak ferromagnetic thin film Cu0.38Ni0.62 has been estimated by using an evolution of the Belov, Goriaga and Arrott (BGA) model. In fact, the typically used measurements of the Zero Field Cooled - Field Cooled magnetic moment m as function the temperature T, the magnetic hysteresis loops m(H) as function of field, and the temperature dependence of the remanent magnetic moment, performed on our sample, did not allow us to individuate precisely the value of Tc, mainly due to the influence of thermal effects and noise on the weak ferromagnetic response of the sample, resulting in a large uncertainty in the estimation of Tc. On the other hand, the also commonly used method of determining the Tc by means of a linear extrapolation of the high field region of m2 as function of the normalized magnetic field H/m at different temperatures (Arrott curves), working though for our analyzed material, could not completely fulfill the basic assumptions of the BGA model in general. For these reasons, we have considered the analysis of the derivatives of the Arrott curves, starting from observing that the Tc of the sample corresponds to the temperature where the curvature of the Arrott curves at low fields inverts. In this way the sensitivity in the determination of the Curie point from the inductive measurements of the magnetic moment is improved while the correct assumptions of the Arrott model are also fully respected.