Order of Magnetic Transitions in La(Fe1-xSix)13 Induced by Random Anisotropy

The temperature dependence of the magnetic moment in La(Fe1-xSix)13 compounds reveals the presence of both first-order and second-order magnetic phase transitions. The nature of the transition is governed by variations in the Si concentration, which induce significant modifications in the FeI–FeII interactions between Fe atoms occupying two non-equivalent sites. These effects can be effectively modeled as a form of random anisotropy, the resulting behavior of which is accurately described within the framework of the Blume-Capel model. Monte Carlo simulations demonstrate that the evolution from a first-order to a second-order magnetic transition in La(Fe1-xSix)13 compounds can be consistently reproduced by maintaining a fixed anisotropy probability p while systematically reducing the corresponding anisotropy amplitude D, yielding good agreement with experimental trends.