Maria Mansurova

Coherent ultrafast spin-dynamics probed in three dimensional topological insulators

Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses’ light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone.

A scenario for magnonic spin-wave traps.

Spatially resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center. This can be attributed to a laser generated temperature profile. We determine a shift of 0.5 GHz in the spin-wave frequency due to the spatial thermal profile induced by the femtosecond pump pulse that persists for up to one nanosecond. Similar experiments are presented for a magnonic crystal composed of a CoFeB-film based antidot lattice with a Damon Eshbach mode at the Brillouin zone boundary and its consequences are discussed.

THz elastic dynamics in finite-size CoFeB-MgO phononic superlattices

In this article, we present the observation of coherent elastic dynamics in a nano-scale phononic superlattice, which consists of only 4 bilayers. We demonstrate how ultra-short light pulses with a length of 40 fs can be utilized to excite a coherent elastic wave at 0.535 THz, which persist over about 20 ps. In later steps of the elastic dynamics, modes with frequency of 1.7 THz and above appear. All these modes are related to acoustic band gaps. Thus, the periodicity strongly manifests in the wave physics, although the system under investigation has only a small number of spatial periods. To further illustrate this, we show how by breaking the translational invariance of the superlattice, these features can be suppressed. Discussed in terms of phonon blocking and radiation, we elucidate in how far our structures can be considered as useful building blocks for phononic devices.

Numerical calculation of laser-induced thermal diffusion and elastic dynamics

In this article we discuss the implementation of a finite-difference time-domain simulation method, which describes thermal diffusion and elastic dynamics induced by an ultrashort laser-pulse. Besides the pseudocode, we provide an example in which numerical results are compared with experimental data, showing excellent agreement.

Magnetization dynamics in magnonic structures with different geometries: interfaces, notches and waveguides

The discovery of ultrafast magnetization dynamics 20 years ago has led to a broad variety of experimental techniques to explore phenomena in magnetic materials with high temporal resolution. In the current article we present a study dealing with broadband excitation of spin-wave packets at different magnonic crystal continuous magnetic film interfaces. Similar to protected conducting states on the surfaces of topological band insulators, these interfaces exhibit surface spin-wave modes that propagate out of the crystal into the continuous film. The propagation distance depends on the direction of the applied magnetic field as well as the surface geometry of the crystal.

Spin-Current Manipulation of Photo-Induced Magnetization Dynamics in Heavy Metal/Ferromagnet Double Layer-Based Nanostructures

Spin currents offer a way to control static and dynamic magnetic properties, and therefore, they are crucial for the next-generation magnetoresistive random access memory devices or spin-torque oscillators. Manipulating the dynamics is especially interesting within the context of photo-magnonics. In typical 3d transition metal ferromagnets, such as CoFeB, the lifetime of light-induced magnetization dynamics is restricted to about 1 ns, which, e.g., strongly limits the opportunities to exploit the wave nature in a magnonic crystal filtering device. Here, we investigate the potential of spin currents to increase the spin-wave lifetime in a functional bilayer system, consisting of a heavy metal [8 nm of

Disentangling Spin and Charge Dynamics with Magneto-Optics

\beta

Confinement of phonon propagation in laser deposited tungsten/polycarbonate multilayers

-Tantalum (Platinum)] and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer generates a transverse spin current when a lateral charge current passes through the strip. Using time-resolved all-optical pump-probe spectroscopy, we investigate how this spin current affects the magnetization dynamics in the adjacent CoFeB layer. We observed a linear spin-current manipulation of the effective Gilbert damping parameter for the Kittel mode from which we were able to determine the system’s spin Hall angles. Furthermore, we measured a strong influence of the spin current on a high-frequency mode. We interpret this mode as an exchange dominated higher order spin-wave resonance. Thus, we infer a strong dependence of the exchange constant on the spin current.

Phonon localization in ultrathin layered structures

The magneto-optical response of Fe and CrO2 epitaxial films has been investigated by pump-probe polarimetry, showing that charge and spin dynamics can be unambiguously disentangled. Both diagonal and off-diagonal terms of the dielectric tensor can be retrieved, providing the complete dynamical characterization of magnetic and optical properties in a ferromagnet.