| We apply a Preisach model of hysteresis to the properties of polycrystalline Sr1-xCaxRuO3 0.0, 0.2, 0.4 and 0.6) and Fe3O4 grain. The model decomposes the magnetization process into reversible and irreversible parts, and decomposes the irreversible part into many magneticunits with moment u0, coercivity hc and bias field hi. . We introduce the temperaturedependence of the free energy and thermal fluctuation to this model. For the samples1-xCaxRuO3 (x=0.0, 0.2, 0.4 and 0.6) and Fe3O4, standard experimental protocols such asto field cooling (ZFC), field cooling (FC) and hysteresis loops under various temperatureshave been simulated by Preisach model, and we get some parameters. The study results showhat the parameters not only embody the changing rule of ZFC/FC moments, but also reflecthe shapes of hysteresis loops. In general, the ZFC moment is always smaller than the FCmoment at low temperature, due to the low applied field and the high magnetic anisotropyField.In the study of Sr1-xCaxRuO3 (x = 0.0, 0.2, 0.4 and 0.6), with the increase of Ca substitution, exchange interaction becomes weaker and weaker, while the perovskite structure becomes more distorted, and the critical temperature gradually decreases. By the analysis of the parameters, we get the superparamagnetism blocking temperatures of these materials. The comparison of the blocking temperature and the critical temperature shows that the magnetic behaviors of the Ru oxides are mainly dominated by anisotropy field. The Barkhausen moments of the samples Sr1-xCaxRuO3 (x=0.0, 0.2, 0.4 and 0.6) are smaller than that of their crystal grain, which indicates the moment reversal take place inside the grain by overcoming pinning of the local domain wall.For the Fe3O4, the study shows that the hysteresis is unconspicuous, the superparamagnetism blocking temperature 105 K is much lower than the critical temperature 580 K. While the Barkhausen moment of Fe3O4 is as much as one crystal grain, which indicates the magnetization of Fe3O4 is mostly irreversible process.In addition, the effects of the coercive field and the thermal activation determine the changing rule of ZFC/FC moment, so we study the ZFC/FC moment of the fluctuation-dominated system and the anisotropy-dominated system. Finally, we discuss howthe fitting parameters influence the shape of various magnetism curves. The spontaneous moment u0 influences the ZFC/FC moment, as the increase of u0, the properties of system shift from the fluctuation-dominated system to the anisotropy-dominated system. The exponents Г,Гc,Гc,Гi effect mainly the ZFC curve of the anisotropy-dominated system. Theparameters Гi affect the curvature of FC curves, and different interaction responses different aggregating degree of the particles. |
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