Atomic long-range order effects on Curie temperature and adiabatic spin-wave dynamics in strained Fe-Co alloy films
2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 94, no 6, 064410Article in journal (Refereed) Published
The strained Fe-Co alloy in body-centered tetragonal (bct) structure has raised considerable interest due to its giant uniaxial magnetocrystalline anisotropy energy. On the basis of the classical Heisenberg Hamiltonian with ab initio interatomic exchange interactions, we perform a theoretical study of fundamental finite temperature magnetic properties of Fe1-xCox alloy films as a function of three variables: chemical composition 0.3 <= x <= 0.8, bct geometry [a, c(a)] arising from in-plane strain and associated out-of-plane relaxation, and atomic long-range order (ALRO). The Curie temperatures T-C(x, a) obtained from Monte Carlo simulations display a competition between a pronounced dependence on tetragonality, strong ferromagnetism in the Co-rich alloy, and the beginning instability of ferromagnetic order in the Fe-rich alloy when c/a -> root 2. Atomic ordering enhances T-C and arises mainly due to different distributions of atoms in neighboring coordination shells rather than altering exchange interactions significantly. We investigate the ordering effect on the shape of the adiabatic spin-wave spectrum for selected pairs (x, a). Our results indicate that long-wavelength acoustic spin-wave excitations show dependencies on x, a, and ALRO similar to those of T-C. The directional anisotropy of the spin-wave stiffness d(x, a) peaks in narrow ranges of composition and tetragonality. ALRO exhibits a strong effect on d for near equiconcentration Fe-Co. We also discuss our findings in the context of employing Fe-Co as perpendicular magnetic recording medium.
Place, publisher, year, edition, pages
American Physical Society , 2016. Vol. 94, no 6, 064410
IdentifiersURN: urn:nbn:se:kth:diva-192737DOI: 10.1103/PhysRevB.94.064410ISI: 000381305100002ScopusID: 2-s2.0-84982957782OAI: oai:DiVA.org:kth-192737DiVA: diva2:974481
QC 201609262016-09-262016-09-202016-09-26Bibliographically approved