Average transient period for precession regimes in magnetic films with dynamic bistability

The average transient time of regular regimes corresponding to the dynamic bistability state is studied using analysis of uniform precession of magnetization of a thin magnetic film. The possibility of controlling the transient process parameter by an additional ac magnetic field in the form of a harmonic of noise signal is established. A new type of stochastic resonance is detected, which corresponds to the probability of high-amplitude precession and is manifested during a short noise action.     

Bifurcation magnetic resonance in films magnetized along hard magnetization axis

We study low-frequency ferromagnetic resonance in a thin film magnetized along the hard magnetization axis performing an analysis of magnetization precession dynamics equations and numerical simulation. Two types of films are considered: polycrystalline uniaxial films and single-crystal films with cubic magnetic anisotropy. An additional (bifurcation) resonance initiated by the bistability, i.e. appearance of two closely spaced equilibrium magnetization states is registered. The modification of dynamic modes provoked by variation of the frequency, amplitude, and magnetic bias value of the ac field is studied. Both steady and chaotic magnetization precession modes are registered in the bifurcation resonance range.     

Stochastic resonance between the limiting cycles of precession dynamics

A new type of stochastic resonance that arises between two precession modes under dynamic bistability conditions and is excited by an alternating magnetic field, including a harmonic signal and a white noise, has been studied using a numerical analysis of the uniform magnetization precession in a thin film. The spectrum of the steady-state dynamics of the system at stochastic resonance has been investigated, and its distinctive features have been revealed for the longitudinal and transverse orientations of the additional alternating field.     

Autoresonance in a ferromagnetic film

Precession of magnetization in a perpendicularly magnetized ferromagnetic film exposed to a circularly or linearly polarized small-amplitude high-frequency magnetic field is studied analytically and numerically. The possibility of autoresonance excitation of a highly nonlinear uniform precession of magnetization and of control over this motion by slowly varying the resonance field or frequency of the high-frequency field is demonstrated.     

Low-field microwave absorption behaviors on single layer magnetic film and exchange coupled multilayer magnetic film

This study examined the magnetization reversal effects on low-field microwave absorption in a Fe_91.6B_2.5N_5.9 single layered film with in-plane uniaxial magnetic anisotropy and a multi-layered film with giant magnetoresistivity using ferromagnetic resonance measurements at 9.84 GHz. Two different kinds of absorption modes were observed at near zero dc field and high dc field. The signals at high-field showed all the features of ferromagnetic resonance due to spin precession. However, the absorption signals at low-field should be associated with the switching field at unsaturated magnetic field region.     

Specific features in precession dynamics of magnetization of a uniaxial magnetic film

The precession dynamics of the magnetization of a film with in-plane uniaxial anisotropy in the case of its biasing along the hard magnetization axis has been analyzed by numerically solving the Landau-Lifshitz equations. It has been revealed that the ferromagnetic resonance spectrum near the magnetic anisotropy field exhibits an additional peak, which is associated with the angular bistability due to the presence of two symmetric angular equilibrium positions. The trajectories of precession motion during biasing along the hard magnetization axis differ substantially from the trajectories corresponding to the biasing along the easy axis.     

Nonlinear regimes of resonance precession of the magnetization in a (111) iron-garnet film

The special features of precessional motion under ferromagnetic resonance conditions with perpen-dicular magnetization of the film are investigated on the basis of a numerical solution of the equations of motion of magnetization in a (111) type iron garnet film. Several nonlinear magnetization precession regimes exist for fixed values of the crystallographic and induced anisotropies. Depending on the value of the magnetizing field and the amplitude of the microwave field, precession occurs around the normal to the film with the third harmonic of the fundamental frequency making a small or large contribution to the nutation motion and with a small or large amplitude of the precession angle. Precession regimes around one of three symmetric directions different from the direction of the normal are possible. Narrow ranges of the static field, where dynamical bistability and regimes with a period which is a multiple of the period of the microwave field are realized, exist.     

Spin-torque ferromagnetic resonance induced by the spin Hall effect

We demonstrate that the spin Hall effect in a thin film with strong spin-orbit scattering can excite magnetic precession in an adjacent ferromagnetic film. The flow of alternating current through a Pt/NiFe bilayer generates an oscillating transverse spin current in the Pt, and the resultant transfer of spin angular momentum to the NiFe induces ferromagnetic resonance dynamics. The Oersted field from the current also generates a ferromagnetic resonance signal but with a different symmetry. The ratio of these two signals allows a quantitative determination of the spin current and the spin Hall angle.     

Ferromagnetic resonance in a uniaxial magnetic film subjected to magnetic biasing along its hard axis

The precession dynamics of the magnetization of a film with an in-plane uniaxial anisotropy is analyzed in the spectrum of ferromagnetic resonance corresponding to magnetic biasing along the hard axis of the film. An additional resonance peak is revealed near magnetic anisotropy field H _u . This peak is related to the appearance of angular bistability due to the presence of two symmetric angular equilibrium positions in field H < H _u .     

Dissipation of spin angular momentum in magnetic switching

Applying one ultrashort magnetic field pulse, we observe up to 10 precessional switches of the magnetization direction in single crystalline Fe films of 10 and 15 atomic layers. We find that the rate at which angular momentum is dissipated in uniform large angle spin precession increases with time and film thickness, surpassing the intrinsic ferromagnetic resonance spin lattice relaxation of Fe by nearly an order of magnitude.     

Nanoscale spin wave localization using ferromagnetic resonance force microscopy

We use the dipolar fields from a magnetic cantilever tip to generate localized spin wave precession modes in an in-plane magnetized, thin ferromagnetic film. Multiple resonances from a series of localized modes are detected by ferromagnetic resonance force microscopy and reproduced by micromagnetic models that also reveal highly anisotropic mode profiles. Modeled scans of line defects using the lowest-frequency mode provide resolution predictions of (94.5±1.5) nm in the field direction, and (390±2) nm perpendicular to the field.     

Spin dynamics of magnetic resonance with parametric modulation in a potassium vapor cell

A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magnetic field. Here we demonstrate both theoretically and experimentally the variations of the resonance condition and the spin precession dynamics resulting from the parametric modulation of the bias field. We show that the driving magnetic field with the frequency detuned by different harmonics of the parametric modulation frequency can lead to resonance as well. Also, a series of frequency sidebands centered at the driving frequency and spaced by the parametric modulation frequency can be observed in the precession of the atomic polarization. We further show that the resonant amplitudes of the sidebands can be controlled by varying the ratio between the amplitude and the frequency of the parametric modulation. These effects could be used in different atomic magnetometry applications.     

The effects of large oscillating fields on spin precession in magnetic resonance

Magnetic resonance of a spin system which is acted upon by a large near-resonance oscillating magnetic field transverse to a static field has been studied experimentally and theoretically for many years. The technique of DEMUR (Double Electron Muon Resonance) has many advantages for such studies. This paper will describe the results of an experiment to study the precession of the muonium triplet near magnetic resonance using DEMUR.     

Spatial confinement of ferromagnetic resonances in honeycomb antidot lattices

We report on a theoretical investigation of the magnetic static and dynamic properties of a thin ferromagnetic film with honeycomb lattice of circular antidots using micromagnetic simulations and analytical calculations. The theoretical model is based on the Landau–Lifshitz equations and directly accounts for the effects of the magnetic state nonuniformity. A direct calculation of local dynamic susceptibility tensor yields that the resonance spectra consist of four different quasi-uniform modes of the magnetization precession related to the confinement of magnetic domains by the hole mesh. Three of four resonant modes follow a two-fold variation with respect to the in-plane orientation of the applied magnetic field. The easy axes of these modes are mutually rotated by 60° and combine to yield the apparent six-fold configurational anisotropy. Additionally, a mode with intrinsic six-fold symmetry behavior exists, as well. Micromagnetic calculations of the local dynamic susceptibility tensor allow identifying the magnetic unit cell areas/domains responsible for each resonance mode.     

Dynamics of nonlinear precession of magnetization in a garnet ferrite film of the (100) type

The dynamics of steady-state resonant magnetization precession setting in under a transverse magnetic bias field in a garnet ferrite film of the (100) type is investigated on the basis of numerical solution of the equation describing the motion of magnetization. The existence of a steady-state dynamic mode in which the magnetization performs undamped spiral motion, as well as of large-amplitude nutation with a period being a multiple of the period of precession, is discovered.     

Some principles in choosing parameters of magnetic resonance tomographs

The problem of amplifying the signal that ensures the visualization of internal organs in the magnetic resonance tomograph due to the optimal selection of some of its parameters has been considered. The operating principle of the tomograph has been analyzed. The relation between the angle of the magnetic moment precession in hydrogen nuclei in an organism, the frequency of the ac magnetic field exciting this precession, and the constant magnetic field used has been determined using quantum-mechanical concepts. This relation makes it possible to determine the optimal parameters for tomograph operation.

     

Effective gyromagnetic ratios in a mixture of noble gases with artificial nuclear magnetization

The precession of nuclear magnetic moments for a noble gas in an external magnetic field upon the laser pumping of nuclear magnetization is considered. A shift of the nuclear magnetic resonance for a mixture of noble gases with different gyromagnetic ratios of nuclei is observed.     

Elastically driven ferromagnetic resonance in nickel thin films

Surface acoustic waves (SAWs) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic-ferroelectric (Ni/LiNbO(3)) hybrid device. We measure the SAW magnetotransmission at room temperature as a function of frequency, external magnetic field magnitude, and orientation. Our data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession. This causes a distinct magnetic field orientation dependence of elastically driven FMR that we observe in both model and experiment.     

Magnetization dynamics under nonlinear ferromagnetic resonance conditions in a (111) film

The equation of motion of magnetization of a garnet ferrite (111) film is solved numerically. It is shown that different regimes of the resonance precession of magnetization are realized depending on the bias and microwave fields; the regimes differ in amplitude and in the shape of their magnetization precession trajectories. In addition, bifurcations occur which lead to an abrupt change in amplitude, to bistability, and to precession with a period that is a multiple of the microwave-field period.     

Production of Fe clusters by collisions of metal vapour with supersonic argon beams

For a spin-polarized plane wave passing through a spin-rotator containing uniform magnetic field, we provide a detailed analysis for solving the appropriate Schrödinger equation. A modified expression for spin precession is obtained which reduces to the standard Larmor precession relation when kinetic energy is very large compared to the spin-magnetic field interaction. We show that there are experimentally verifiable regimes of departure from the standard Larmor precession formula. The treatment is then extended to the case of a spin-polarized wave packet passing through a uniform magnetic field. The results based on the standard expression for Larmor precession and that obtained from the modified formula are compared in various regimes of the experimental parameters.