Predicting magnetization of ferromagnetic binary Fe alloys from chemical short range order

Abstract

Among the ferromagnetic binary alloys, body centered cubic (bcc) Fe-Co is the one showing the highest magnetization. It is known experimentally that ordered Fe-Co structures show a larger magnetization than the random solid solutions with the same Co content. In this work, based on density functional theory (DFT) studies, we aim at a quantitative prediction of this feature, and point out the role of the orbital magnetic moments. Then, we introduce a DFT-based analytical model correlating local magnetic moments and chemical compositions for Co concentrations ranging from 0 to 70 at.%. It is also extended to predict the global magnetization of both ordered and disordered structures at given concentration and chemical short range orders. The latter model is particularly useful for interpreting experimental data. Based on these models, we note that the local magnetic moment of a Fe atom is mainly dictated by the Co concentration in its first two neighbor shells. The detailed local arrangement of the Co atoms has a minor effect. These simple models can fully reproduce the difference in magnetization between the ordered and disordered Fe-Co alloys between 30% and 70% Co, in good agreement with experimental data. Finally, we show that a similar model can be established for another bcc binary Fe alloy, the Fe-Ni, also presenting ferromagnetic interactions between atoms.

Ground-state properties and lattice-vibration effects of disordered Fe-Ni systems for phase stability predictions

“…Then the magnetization decreases again because Fe moments increase at a slower rate (0.06 μ B per 10% Ni [33]) and the magnetic dilution effect becomes dominant again. Please note that the Fe and Ni moments do not necessarily follow the trend of the magnetization and have local-composition dependence [44]. Indeed, it is found that the local chemical environment has a large impact on the magnetic moments than the local atomic volumes [33].…”

Effective interaction model for coupled magnetism and phase stability in bcc Fe-Co systems

“…13 (d). This result may be associated to the electronic properties of Fe and Co atoms in pure and Fe-Co systems where Co has an essentially saturated magnetism, while Fe can still enhance its magnetism in the presence of excitations, by for example, shifting down the highest peak in the majority-spin states of Fe atoms towards the Fermi level in Fe-Co structures [43].…”

“…( 1) corresponds to the Heisenberg model with ij J being the exchange-coupling parameter for the magnetic moments of ith and j-th atoms. However, unlike the traditional Heisenberg model in which the amplitude of an atomic moment is fixed, the magnetic part of the model (1) takes into account the longitudinal spin fluctuation due to the effect of the local environment as observed by the DFT calculations [43],…”

“…This equation is obtained from the analyses of the effect of the local environment on magnetic moments in bcc Fe-Co systems that are presented in detail in Ref. [43]. In Eq.…”

Effect of Co and Ni Doping on the Structure, Magnetic and Magnetocaloric Properties of Fe-Rich (Mn,Fe)2(P,Si) Compounds

“…This behaviour suggests that Fe-rich (Mn,Fe,Co) 1.95 (P,Si) alloys might exhibit a similar magnetic behaviour as the Fe-Co alloys. Various studies show that the average magnetic moment of Fe-Co alloy reaches the highest value for a small Co content (20-25 at.%) before a decrease is observed [36][37][38]. The reason responsible for a rapid increase in M s for a small Co doping is complex and is related to changes in the magnetic moment and electronic structure [39].…”