Unraveling the role of Sm 4f electrons in the magnetism of SmFeO3

Abstract

Magnetic rare-earth orthoferrites RFeO 3 host a variety of functional properties from multiferroicity and strong magnetostriction to spin-reorientation transitions and ultrafast light-driven manipulation of magnetism, which can be exploited in spintronics and next-generation devices. Among these systems, SmFeO 3 is attracting particular interest for its rich phase diagram and the high temperature Fe-spin magnetic transitions, which combines with a very low temperature and as yet unclear Sm-spin ordering. Various experiments suggest that the interaction between the Sm and Fe magnetic moments (further supported by the magnetic anisotropy), is at the origin of the complex cascade of transitions, but a conclusive and clear picture has not yet been reached. In this paper, by means of comprehensive first-principles calculations, we unravel the role of the magnetic Sm ions in the Fe-spin reorientation transition and in the detected anomalies in the lattice vibrational spectrum, which are a signature of a relevant spin-phonon coupling. By including both Smf electrons and noncollinear magnetism, we find frustrated and anisotropic Sm interactions, and a large magnetocrystalline anisotropy mediated by the SOC of the Sm-4 f electrons, which drive the complex magnetic properties and phase diagram of SmFeO 3 .

Role of Dy 4f electrons on magnetic coupling and reorientation in DyFeO3

“…by changing them to fit the computed electronic band gaps or the deduced magnetic interactions to experimentally measured ones. Herein, the effective Hubbard U eff corrections on localized Dy 4f and Fe 3d states were fixed to 6.0 and 4.5 eV, respectively, throughout the text, similar to available reports [18,21]. In addition, tentative calculations with different U eff ranges (6.0-8.0 eV on Dy 4f ; 3.5-4.5 eV on Fe 3d) implied that they do not substantially change the strength of magnetic interactions, and subsequently, the magnetic transition temperatures.…”

“…Besides, the 4f electrons of rare earth ions are generally considered as core states, and naturally it is not applicable to determine the R 3+ −Fe 3+ spin interaction in their studies. Several theoretical reports, nevertheless, proved that the assign of 4f electrons as valence states is an imperative ingredient to properly capture physical properties of RFeO 3 orthoferrites, particularly for magnetism [18] and spin reorientation [21]. As far as we know, concerning the stealthy impact of Dy 4f electrons on rich magnetic phase diagram and spin reorientation of DyFeO 3 , a clear and convincing picture, which is desirable, has not yet been accomplished.…”