Damping Of Magnetization Precession Research Articles

Role of intersublattice exchange interaction in ultrafast longitudinal and transverse magnetization dynamics in permalloy

We report on element-specific measurements of ultrafast demagnetization and magnetization precession damping in permalloy thin films. Magnetization dynamics induced by an optical pump at 1.5 eV is probed simultaneously at the ${M}_{2,3}$ edges of Ni and Fe with high-order harmonics for moderate demagnetization rates (less than 50%). The role of the intersublattice exchange interaction in both longitudinal and transverse dynamics is analyzed with a Landau-Lifshitz-Bloch description of ferromagnetically coupled Fe and Ni sublattices. It is shown that the intersublattice exchange interaction governs the dissipation during demagnetization as well as precession damping of the magnetization vector.

Influence of adjacent layers on the damping of magnetization precession in CoxFe100-x films

We have measured magnetic damping in polycrystalline Co25Fe75 films adjacent to various nonmagnetic materials (Ti, Cu, Au, NiO) serving as buffer and/or cover layers. It was shown that it is crucial to use a proper buffer layer to achieve low damping in the Co25Fe75 layer. We found that even an ultrathin Cu buffer layer is sufficient to reduce the total damping when inserted between the substrate and the Co25Fe75 layer. The damping measured in the in-plane configuration reduces almost threefold (to αtot< 0.003). Moreover, the Co25Fe75 films with a Cu buffer layer possess low inhomogeneous linewidth broadening, in contrast to those with Au or Ti buffer layers. Using spin pumping into a dielectric antiferromagnetic capping layer (NiO), we determined that the effective spin mixing conductance is 4.8 × 1019 m−2. This value is large compared to those of Pt, Pd, and Au.

The role of elastic dissipation in the formation of magnetization precession in magnetoelastic medium

As applied to the problem of reducing the noise of a rotational magnetometer, the formation of damping of magnetization precession due to elastic dissipation in magnetoelastic medium is considered. It is shown that, at a large enough elastic dissipation, the effectiveness of its contribution to the magnetic dissipation sharply decreases.

Comparison of micromagnetic parameters of the ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As

We report on the determination of micromagnetic parameters of epilayers of the ferromagnetic semiconductor (Ga,Mn)As, which has an easy axis in the sample plane, and (Ga,Mn)(As,P), which has an easy axis perpendicular to the sample plane. We use an optical analog of ferromagnetic resonance where the laser-pulse-induced precession of magnetization is measured directly in the time domain. By the analysis of a single set of pump-and-probe magneto-optical data, we determined the magnetic anisotropy fields, the spin stiffness, and the Gilbert damping constant in these two materials. We show that incorporation of 10% of phosphorus in (Ga,Mn)As with 6% of manganese leads not only to the expected sign change of the perpendicular-to-plane anisotropy field but also to an increase of the Gilbert damping and to a reduction of the spin stiffness. The observed changes in the micromagnetic parameters upon incorporating P in (Ga,Mn)As are consistent with the reduced hole density, conductivity, and Curie temperature of the (Ga,Mn)(As,P) material. We also show that the apparent magnetization precession damping is stronger for the $n=1$ spin wave resonance mode than for the $n=0$ uniform magnetization precession mode.

Magnetic-stress-assisted damping of magnetization precession in multilayered metallic films

Micromagnetic dynamics of spin relaxation in multilayered metallic films of stacked microelectronic devices is modeled by a modified Landau–Lifshitz–Gilbert equation with a newly introduced form of damping torque owing its origin to coupling between precessing magnetization-vector and stress-tensor of combined intrinsic and extrinsic magnetic anisotropy. Based on the magnetization energy loss equation, the exponential relaxation time as a function of precession frequency and angle of applied rf-field is obtained, depending upon two parameters of intrinsic and extrinsic damping torques acting on precessing magnetization. It is shown that theoretically obtained from the Gabor uncertainty relation the FMR linewidth, originating from the above magnetic-stress-assisted damping of magnetization precession, provides proper account for the empirical non-linear linewidth-vs-frequency curves deduced from recent in-plane FMR measurements on multilayered ultrathin films of ferromagnetic metals.

Damping modulated terahertz emission of ferromagnetic films excited by ultrafast laser pulses

Ultrafast demagnetization processes in ferromagnetic films have been shown to produce terahertz (THz) emission. We present an experimental demonstration that, following ultrafast optical excitation, the magnitude of terahertz electromagnetic pulses emitted from a ferromagnetic film is proportional to the Gilbert damping constant, which is conventionally used to describe the damping of magnetization precession. The damping of a ferromagnetic thin film is tuned by using an adjacent nonmagnetic layer, which does not change the magnetization and anisotropy of the ferromagnetic film, allowing an unambiguous determination of the relationship between the THz emission and the damping constant.

Spin Dynamics in (III,Mn)V Ferromagnetic Semiconductors: The Role of Correlations

We address the role of correlations between spin and charge degrees of freedom on the dynamical properties of ferromagnetic systems governed by the magnetic exchange interaction between itinerant and localized spins. For this we introduce a general theory that treats quantum fluctuations beyond the random phase approximation based on a correlation expansion of the Green's function equations of motion. We calculate the spin susceptibility, spin-wave excitation spectrum, and magnetization precession damping. We find that correlations strongly affect the magnitude and carrier concentration dependence of the spin stiffness and magnetization Gilbert damping.

Light-induced magnetization precession in GaMnAs

We report the dynamics of the transient polar Kerr rotation (KR) and of the transient reflectivity induced by femtosecond laser pulses in ferromagnetic (Ga,Mn)As with no external magnetic field applied. It is shown that the measured KR signal consists of several different contributions, among which only the oscillatory signal is directly connected with the ferromagnetic order in (Ga,Mn)As. The origin of the light-induced magnetization precession is discussed and the magnetization precession damping (Gilbert damping) is found to be strongly influenced by annealing of the sample.

Coherent magnetization precession in GaMnAs induced by ultrafast optical excitation

The authors use femtosecond optical pulses to induce, control, and monitor magnetization precession in ferromagnetic Ga0.965Mn0.035As. At temperatures below ∼40K, they observe coherent oscillations of the local Mn spins, triggered by an ultrafast photoinduced reorientation of the in-plane easy axis. The amplitude saturation of the oscillations above a certain pump intensity indicates that the easy axis remains unchanged above ∼TC∕2. The authors find that the observed magnetization precession damping (Gilbert damping) is strongly dependent on pump laser intensity, but independent of ambient temperature. They provide a physical interpretation of the observed light-induced collective Mn-spin precession and relaxation.

Size dependent damping in picosecond dynamics of single nanomagnets

The authors use time-resolved cavity-enhanced magneto-optical Kerr spectroscopy to study the damping of magnetization precession in individual cylindrical nickel nanomagnets. A wide range of shapes (diameters of 5μm–125nm and aspect ratio: 0.03–1.2) is investigated. They observe a pronounced difference in damping between the micro- and nanomagnets. Microscale magnets show large damping at low bias fields, whereas nanomagnets exhibit bias field-independent damping. This behavior is explained by the interaction of in-plane and out-of-plane precession modes in microscale magnets that results in additional dissipative channels. The small and robust damping values on the nanoscale are promising for implementation of controlled precessional switching schemes in nanomagnetic devices.