It is known that the use of light diffraction makes it possible to improve the spatial resolution of magneto-optical methods. The image of a two-domain structure obtained in the domain wall contrast makes it possible to consider such a structure as a "gray" slit. In this paper, we consider the problem of light diffraction by a "gray" slit and discuss the possibilities of using the obtained results in high-speed photography and in the pump-probe method.

It is shown using the technique of double high-speed photography that an external magnetic field triggers the motion of a GdFeCo domain wall with a velocity up to 1.2 km/s. The domain wall velocity increases and levels off with an increase in the amplitude of the driving magnetic-field pulse. In contrast to the earlier experiments on iron ferrites, no influence of femtosecond laser pulses on the domain wall dynamics has been observed, even when the pump pulse energy is sufficient for magnetization reversal.

Using the technique of double high-speed photography method, we show that an external magnetic field triggers in GdFeCo domain wall motion with velocities up to 1.2 km / s. The domain wall velocity saturates with an increase of the driving magnetic field. Contrary to earlier experiments on iron garnets, we did not succeed to detect any effect of femtosecond laser pulses on the domain wall velocity, even if the pulses were strong enough to reverse magnetization.

Using diffraction of femtosecond laser pulses of visible light by a magnetic domain pattern in an iron garnet, we demonstrate a proof of concept of time-resolved measurements of domain pattern movements with nanometer spatial and femtosecond temporal resolution. In this method, a femtosecond laser (pump) pulse initiates magnetization dynamics in a sample that is initially in a labyrinth domain state, while an equally short linearly polarized laser pulse (probe) is diffracted by the domain pattern. The components of the diffracted light that are polarized orthogonally to the incident light generate several concentric diffraction rings. Nanometer small changes in the relative sizes of domains with opposite magnetization result in observable changes in the intensities of the rings. We demonstrate that the signal-to-noise ratio is high enough to detect a 6 nm domain wall displacement with 100 fs temporal resolution using visible light. We also discuss possible artifacts, such as pump-induced changes of optical properties, that can affect the measurements.

The influence of the parameters of the control pulse of a magnetic field with the shape of a rectangular trapezoid on the dynamics of domain walls in ferrite garnets and orthoferrites is studied. The calculation results are compared with experimental data obtained by the high-speed photography method. It is shown that the front edge of the control pulse with duration of less than 80 ns has a slight effect on the dynamics of the domain wall in materials in which the velocity of domain wall motion does not exceed several hundred meters per second. If the domain wall velocity is several kilometers per second, then a front edge with a duration of 50 ns leads to long acceleration of the domain wall to the maximum velocity and reduces the time required for the wall to move with this velocity, thereby limiting the possibility of additional control over the wall dynamics. It is shown that an excessively long front edge of the pulse can lead to a decrease in the maximum velocity of the domain wall and its mobility in the experimental measurements. An excessively short control pulse with a fixed amplitude leads to a decrease in the maximum displacement of the domain wall and, consequently, to a decrease in the time of motion with a constant velocity that corresponds to a given amplitude of the control pulse.

Using a method that combines double high-speed photography and a pump-probe method, it was found that a femtosecond laser pulse is able to change the domain wall velocity in a ferrite–garnet film. The change in the velocity of the domain wall depends on both the energy of the pump pulse and the domain wall velocity itself, and does not depend on the pump pulse polarization. This result is not associated with local magnetization reversal and cannot be explained by local heating of the material, since a temperature increasing leads to an increase of the domain wall mobility. To explain the results, we propose a model in which the domain wall velocity is controlled by the photo-induced generation of vertical Bloch lines.

Optical pump-probe setups are commonly used for excitation and investigation of the spin dynamics in various types of magnetic materials. However, usually the spatially homogeneous excitation is considered. In the present study we describe an approach for optical excitation of the nonuniform THz spin dynamics and for probing its spatial distribution inside a magnetic crystal. We propose to illuminate a crystal with laser pulses of properly adjusted polarization to benefit from a strong optical birefringence inherent to the crystal. It results in an unusual behavior of the effective magnetic field generated by the pulses due to the inverse Faraday effect and the peculiar sign-changing dependence of the direct Faraday effect inside the crystal. The study is performed exemplary for yttrium orthoferrite crystal although the proposed approach is applicable for various magnetic materials with optical anisotropy.

Using the double high-speed photography method, the dynamics of domain walls in a ferrite–garnet film is studied under an in-plane magnetic field close in magnitude to the anisotropy field. To explain the obtained nonlinear relation between the domain wall mobility and dc magnetic field oriented in the film plane perpendicular to the domain wall plane, we use the assumption about the dependence of the damping parameter on the in-plane field, which becomes appreciable under the in-plane field exceeding 40% of the sample anisotropy field.

Using the technique of double high-speed photography, we find that a femtosecond laser pulse is able to change the velocity of a moving domain wall in an yttrium iron garnet. The change depends on the light intensity and the domain wall velocity itself. To explain the results we propose a model in which the domain wall velocity is controlled by photo-induced generation of vertical Bloch lines.

A heat-assisted route for subnanosecond magnetic recording is discovered for the dielectric bismuth-substituted yttrium iron garnet, known for possessing small magnetic damping. The experiments and simulations reveal that the route involves nonlinear magnetization precession, triggered by a transient thermal modification of the growth-induced crystalline anisotropy in the presence of a fixed perpendicular magnetic field. The pathway is rendered robust by the damping becoming anomalously large during the switching process. Subnanosecond deterministic magnetization reversal was achieved within just one-half of a precessional period, and this mechanism should be possible to implement in any material with suitably engineered dissimilar thermal derivatives of magnetization and anisotropy.

Experimental and theoretical investigations of solitary domain wall dynamics in an yttrium orthoferrite plate under the action of a pulse magnetic field were carried out. The investigations are performed under conditions in which the change in the gradient magnetic field is comparable to the magnitude of the pulse magnetic field shifting the domain walls when the latter are displaced from their equilibrium position.

Femtosecond time-resolved Faraday rotation is studied in magnetic garnet films and magnetophotonic crystals. Femtosecond dynamics of Faraday angle governed by multiple reflection interference and Faraday effect non-reciprocity is revealed by using polarization-sensitive ultrafast correlation technique.