Systematic study of magnetodynamic properties at finite temperatures in doped permalloy from first-principles calculations

Abstract

By means of first principles calculations, we have systematically investigated how the magnetodynamic properties Gilbert damping, magnetization and exchange stiffness are affected when permalloy (Py) (Fe0.19Ni0.81) is doped with 4d or 5d transition metal impurities. We find that the trends in the Gilbert damping can be understood from relatively few basic parameters such as the density of states at the Fermi level, the spin-orbit coupling and the impurity concentration. The temperature dependence of the Gilbert damping is found to be very weak which we relate to the lack of intraband transitions in alloys. Doping with 4d elements has no major impact on the studied Gilbert damping, apart from diluting the host. However, the 5d elements have a profound effect on the damping and allows it to be tuned over a large interval while maintaining the magnetization and exchange stiffness. As regards spin stiffness, doping with early transition metals results in considerable softening, whereas late transition metals have a minor impact. Our result agree well with earlier calculations where available. In comparison to experiments, the computed Gilbert damping appears slightly underestimated while the spin stiffness show good general agreement.

Extended spin model in atomistic simulations of alloys

“…We focus on a few intricate features that could only be displayed in random alloys. First of all, the size of Fe moments in Py is calculated to be larger than it is in the elemental Fe while the moment size of Ni has roughly the same value, as expected from other studies 55 . Moreover, compared to the elemental Fe where moment sizes are rather constant, the local Fe moments in Py are more strongly reduced, in particular above T c .…”

Spin wave stiffness and exchange stiffness of doped permalloy via ab initio calculations

“…Regarding the absolute numbers, there are some differences, both between our theory and experiment and between our theory and earlier calculations. In particular our value of the spin wave stiffness D for undoped permalloy Fe 19 Ni 81 of 576 meV Å2 is higher than 515 meV Å2 obtained by Yu et al [30] via the tightbinding linear muffin-tin orbital method or 522 meV Å2 obtained by Pan et al [4] via the KKR-Green's func- Recent experimental values for D of Py are 390 meV Å2 [31] and 440 meV Å2 [26], i.e., less than the theoretical values. This is probably linked to problems with describing the exchange coupling of Ni in terms of the coupling constants J ij -there is an even larger difference between theory and experiment for D of fcc Ni [9,30].…”

“…Recently the applicability of Eq. ( 5) was extended to multicomponent systems [4,10,11]. In our case we are dealing with doped Py so we have atoms of three different types located on lattice sites of an fcc structure.…”

“…Yin et al [3] studied the magnetic properties of Py doped with noble metals Ag, Pt, and Au and found a good agreement between theoretical and experimental values of A ex for dopant concentrations 10-30 %. In another study the effect of doping Py by 4d and 5d elements on the stiffness was studied theoretically for modest concentrations (5-15 %) but corresponding experimental data for comparison are lacking [4]. On the other hand, experimental data are available for Py doped with V, Gd, and Pt with concentrations from 1 % to 10 % thanks to the works of Lepadatu et al [5,6] and Hrabec et al [7].…”

Temperature and Thickness Dependence of Statistical Fluctuations of the Gilbert Damping in Co - Fe - BSampan-a-pai1, Chureemart2, Chantrell3 et al. 2019Phys. Rev. Applied124110View full textAdd to dashboardCite

“…Physically, the high damping at the interface is expected to be due to the hybridization of the interfacial Fe layer, leading to a strong perpendicular interfacial anisotropy. In general, spin and lattice fluctuations are expected to contribute weakly to the Gilbert damping at temperatures significantly below the Curie and melting temperatures [16]. The spin-orbit coupling provides an energy dissipation channel for precessing spins at the interface.…”