Direct observation of dynamic modes excited in a magnetic insulator by pure spin current.

Excitation of magnetization dynamics by pure spin currents has been recently recognized as an enabling mechanism for spintronics and magnonics, which allows implementation of spin-torque devices based on low-damping insulating magnetic materials. Here we report the first spatially-resolved study of the dynamic modes excited by pure spin current in nanometer-thick microscopic insulating Yttrium Iron Garnet disks. We show that these modes exhibit nonlinear self-broadening preventing the formation of the self-localized magnetic bullet, which plays a crucial role in the stabilization of the single-mode magnetization oscillations in all-metallic systems.

Generation of coherent spin-wave modes in yttrium iron garnet microdiscs by spin-orbit torque.

In recent years, spin-orbit effects have been widely used to produce and detect spin currents in spintronic devices. The peculiar symmetry of the spin Hall effect allows creation of a spin accumulation at the interface between a metal with strong spin-orbit interaction and a magnetic insulator, which can lead to a net pure spin current flowing from the metal into the insulator. This spin current applies a torque on the magnetization, which can eventually be driven into steady motion.

Efficient Synchronization of Dipolarly Coupled Vortex-Based Spin Transfer Nano-Oscillators.

Due to their nonlinear properties, spin transfer nano-oscillators can easily adapt their frequency to external stimuli. This makes them interesting model systems to study the effects of synchronization and brings some opportunities to improve their microwave characteristics in view of their applications in information and communication technologies and/or to design innovative computing architectures. So far, mutual synchronization of spin transfer nano-oscillators through propagating spinwaves and exchange coupling in a common magnetic layer has been demonstrated.

Full control of the spin-wave damping in a magnetic insulator using spin-orbit torque.

It is demonstrated that the threshold current for damping compensation can be reached in a 5  μm diameter YIG(20  nm)|Pt(7  nm) disk. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of I(dc) using a magnetic resonance force microscope (MRFM). It is shown that the magnetic losses of spin-wave modes existing in the magnetic insulator can be reduced or enhanced by at least a factor of 5 depending on the polarity and intensity of an in-plane dc current I(dc) flowing through the adjacent normal metal with strong spin-orbit interaction.

Origin of spectral purity and tuning sensitivity in a spin transfer vortex nano-oscillator.

We investigate the microwave characteristics of a spin transfer nano-oscillator (STNO) based on coupled vortices as a function of the perpendicular magnetic field H(⊥). Interestingly, we find that our vortex-based oscillator is quasi-isochronous independently of H(⊥) and for a dc current ranging between 18 and 25 mA. It means that the severe nonlinear broadening usually observed in STNOs can be suppressed on a broad range of bias.

Probing the anharmonicity of the potential well for a magnetic vortex core in a nanodot.

The anharmonicity of the potential well confining a magnetic vortex core in a nanodot is measured dynamically with a magnetic resonance force microscope (MRFM). The stray field of the MRFM tip is used to displace the equilibrium core position away from the nanodot center. The anharmonicity is then inferred from the relative frequency shift induced on the eigenfrequency of the vortex core translational mode.

Detection of microwave spin pumping using the inverse spin Hall effect.

We report on the electrical detection of the dynamical part of the spin-pumping current emitted during ferromagnetic resonance using inverse spin Hall effect methods. The experiment is performed on a YIG|Pt bilayer. The choice of yttrium iron garnet (YIG), a magnetic insulator, ensures that no charge current flows between the two layers and only the pure spin current produced by the magnetization dynamics is transferred into the adjacent strong spin-orbit Pt layer via spin pumping.

Measurement of the dynamical dipolar coupling in a pair of magnetic nanodisks using a ferromagnetic resonance force microscope.

We perform a spectroscopic study of the collective spin-wave dynamics occurring in a pair of magnetic nanodisks coupled by the magnetodipolar interaction. We take advantage of the stray field gradient produced by the magnetic tip of a ferromagnetic resonance force microscope to continuously tune and detune the relative resonance frequencies between two adjacent nano-objects. This reveals the anticrossing and hybridization of the spin-wave modes in the pair.

Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks.

Spin-wave spectra of perpendicularly magnetized disks consisting of a 100 nm permalloy layer sandwiched between two Cu layers of 30 nm are measured individually by a magnetic resonance force microscope. Using 3D micromagnetic simulations, it is demonstrated that, for submicron-size diameters, the lowest energy spin-wave mode of the saturated state is not spatially uniform, but rather is localized at the center of the Py/Cu interfaces in the region of the minimum demagnetizing field.