Magnetic relaxations in metallic multilayers

Abstract

Abstract-The intrinsic damping mechanism in metals caused by incoherent scattering of itinerant electron-hole pair excitations by phonons and magnons will be reviewed. The unique features of magnetic relaxations in multilayers were studied by ferromagnetic resonance (FMR) using magnetic single, Au-Fe-GaAs(001), and double layer Au-Fe-Au-Fe-GaAs(001) structures prepared by molecular beam epitaxy. The magnetic relaxation in single-layer films is described by the Gilbert damping with no extrinsic contributions to the FMR linewidth. These films provided an excellent opportunity to investigate nonlocal damping. The main result of these studies is that ultrathin Fe films in magnetic double layers acquire an additional interface Gilbert damping. This is in agreement with recent predictions of nonlocal interface damping which is based on the transport of spin angular momentum between the ferromagnetic layers. Measurements of the nonlocal Gilbert damping offer a possibility to carry out quantitative studies of the relaxation torques caused by nonlocal spin momentum transfer. Numerical simulations of magnetization reversal and stationary precession for an applied perpendicular current in Au-Fe-Au-Fe-GaAs(001) multilayers will be shown.Index Terms-Ferromagnetic resonance, magnetic multilayers, nonlocal spin relaxations.

Role of dynamic exchange coupling in magnetic relaxations of metallic multilayer films (invited)

“…By using the same interaction potential it is shown 16,28 that the Gilbert damping from the dynamic interlayer exchange coupling, G sϪd , is similar to that using the spinpumping theory 8 combined with a perfect spin sink. This leads to an important conclusion: The spin pumping theory is equivalent to the dynamic response of the interlayer exchange coupling.…”

“…2,26,27 The in-plane ferromagnetic resonance ͑FMR͒ experiments were carried out using 10, 24, 36, and 72 GHz systems. 3 Single Fe ultrathin films with thicknesses of 8,11,16,21, and 31 monolayers ͑MLs͒ were grown directly on GaAs͑001͒.…”

“…͑11͒ allows one to account for electron-electron correlation effects in the normal metal. It has been shown 16,28 that the Gilbert damping is enhanced by the square of the Stoner factor S E ϭ͓1…”

Semiclassical theory of spin transport in magnetic multilayers

“…The internal magnetic field is treated by employing Maxwell's equations. A precessing magnetization in FM creates a spin current which is described by spin pumping proposed by Tserkovnyak et In our recent ferromagnetic resonance ͑FMR͒ studies [1][2][3][4] it was shown that the transfer of the spin momentum across ferromagnetic ͑FM͒/normal metal ͑NM͒ interfaces can result in nonlocal interface Gilbert damping GЈ. The generation of spin momentum in magnetic ultrathin films was theoretically described by Tserkovnyak et al 5 and the effect was called ''spin pumping.''…”

“…The presence of a second magnetic layer creates a spin sink. 3,4,6,7 The combination of spin pump and spin sink in the ballistic limit leads to an additional interface Gilbert damping. In this article we extend the spin pump and spin sink mechanisms to the nonballistic electron transport which includes a full treatment of the Landau-Lifshitz ͑LL͒ equation of motion in FM and diffusion equation in NM and Maxwell's equations accounting for a finite penetration of the rf fields.…”