Enhancement of intrinsic magnetic damping in defect-free epitaxial Fe3O4 thin films

Abstract

We have investigated the magnetic damping of precessional spin dynamics in defect-controlled epitaxial grown Fe 3 O 4 (111)/Yttria-stabilized Zirconia (YSZ) nanoscale films by all-optical pump-probe measurements. The intrinsic damping constant of the defect-free Fe 3 O 4 film is found to be strikingly larger than that of the asgrown Fe 3 O 4 film with structural defects. We demonstrate that the population of the first-order perpendicular standing spin wave (PSSW) mode, which is exclusively observed in the defect-free film under sufficiently high external magnetic fields, leads to the enhancement of the magnetic damping of the uniform precession (Kittel) mode. We propose a physical picture in which the PSSW mode acts as an additional channel for the extra energy dissipation of the Kittel mode. The energy transfer from Kittel mode to PSSW mode increases as in-plane magnetization precession becomes more uniform, resulting in the unique intrinsic magnetic damping enhancement in the defect-free Fe 3 O 4 film.The photo-induced precessional spin dynamics in various magnetic materials has attracted significant attention since the observation of the uniform magnetic precession (Kittel mode) and the corresponding first-order perpendicular standing spin wave (PSSW mode) in Ni films by the all-optical pump-probe technique. 1,2 After excitation by a femtosecond laser pulse, besides the uniform Kittel mode, different spin wave modes can be stimulated including first-order PSSW and Damon-Eshbach dipolar surface spin waves (DE modes). 3 At the same time, all-optical pump-probe measurements allow determination of the magnetic Gilbert damping α, 4,5 which is a key parameter for magnetic data recording and the nextgeneration spintronic memory devices such as Magnetoresistive Random Access Memory (MRAM) 6,7 . Therefore, understanding and controlling the magnetic damping is of crucial importance. Among many factors affecting the magnetic damping, structural defects are crucial because they are generally inevitable when preparing films or devices. It was proposed theoretically that defects scatter the Kittel mode into short wavelength spin waves via two magnon scattering, producing an extrinsic contribution to magnetic damping. 8 This extrinsic mechanism was verified by the fact that in thin NiFe films the FMR linewidth increases with decreasing thickness. 9

The role of faceting and elongation on the magnetic anisotropy of magnetite Fe3O4 nanocrystals

“…and a heat bath which aligns the magnetization along the field direction. In this atomistic formulation of the sLLG, λ = 0.063 represents the local intrinsic contributions of spin-lattice and spin-electron interactions and is extracted from experimental data for the effective Gilbert damping for magnetite thin films 51 .…”

“…The first term of the sLLG describes the precession of the atomic spins and arises due to their quantum mechanical interaction with the effective magnetic field, and the second term describes direct angular momentum transfer between the spins 11/16 and a heat bath which aligns the magnetization along the field direction. In this atomistic formulation of the sLLG, λ = 0.063 represents the local intrinsic contributions of spin-lattice and spin-electron interactions and is extracted from experimental data for the effective Gilbert damping for magnetite thin films 51 .…”

Strain‐Controlled Spin Wave Excitation and Gilbert Damping in Flexible Co2FeSi Films Activated by Femtosecond Laser Pulse

“…It has been reported that multimode spin wave excitation can lead to enhanced magnetic damping, since the spin waves provide additional channels for the energy dissipation of the Kittel mode. [ 48 ] However, this cannot account for the decrease in damping of the compressive‐strained Co 2 FeSi film, which implies other strain‐related damping mechanism to be explored.…”

“…Figure 4b shows the lifetimes of the Kittle modes reflecting the intrinsic Gilbert damping as the external field approaches infinity. [36] From the Kittle mode lifetime τ, [48,49] one can follow to derive the effective damping © 2021 Wiley-VCH GmbH constant α eff using the relation α eff = (2πfτ) −1 . It is noteworthy that the lifetime of the Kittle mode is strongly strain-dependent and so as α eff .…”

Role of anti-phase boundaries in the formation of magnetic domains in magnetite thin films

“…Although the damping constant has been predicted to have small values for magnetite [19], we chose critical damping λ = 1 in this work in order to describe the influence of the APB on the quasi-equilibrium magnetic properties of magnetite. Therefore, we focus on the final magnetization state of our simulations but not on its dynamics.…”