Showing papers by "Andrzej Maziewski published in 2016"

Non-thermal optical excitation of terahertz-spin precession in a magneto-optical insulator

Abstract: We demonstrate non-thermal ultrafast laser excitation of spin precession with THz frequency in Gd-Bi-substituted iron garnet via the inverse Faraday effect. The modulation of THz precession by about 60 GHz below the compensation temperature of magnetic moment was observed. The THz frequency precession was caused by the exchange resonance between the Gd and Fe sublattices; we attributed the low-frequency modulation to dielectric resonance mode with a magnetic contribution. We demonstrate the possibility of polarization-sensitive control of spin precession under THz generation by laser pulses, helping to develop high-speed magneto-optical devices.

Magnetic phases in Pt/Co/Pt films induced by single and multiple femtosecond laser pulses

Abstract: Ultrathin Pt/Co/Pt trilayers with initial in-plane magnetization were irradiated with femtosecond laser pulses. In this way, an irreversible structural modification was introduced, which resulted in the creation of numerous pulse fluence-dependent magnetic phases. This was particularly true with the out-of-plane magnetization state, which exhibited a submicrometer domain structure. This effect was studied in a broad range of pulse fluences up to the point of ablation of the metallic films. In addition to this single-pulse experiment, multiple exposure spots were also investigated, which exhibited an extended area of out-of-plane magnetization phases and a decreased damage threshold. Using a double exposure with partially overlapped spots, a two-dimensional diagram of the magnetic phases as a function of the two energy densities was built, which showed a strong inequality between the first and second incoming pulses.

Photoinduced Ultrafast Magnetization Dynamics in Yttrium-Iron Garnet and Ultrathin Co Films

Abstract: We report experimental studies on ultrafast laser-induced magnetization dynamics on a picosecond time scale in ultrathin Co/garnet heterostructures. We compare polarization-sensitive nonthermal dynamics in garnet triggered via photoinduced anisotropy with the thermal dynamics in 2 nm Co films. The influence of Gilbert damping on frequency of magnetization precession under an external magnetic field in a garnet film is described. Thermal demagnetization with a 0.81 ps characteristic time is in good agreement with a two-temperature model of electron-lattice coupling.

Geometrical complexity of the antidots unit cell effect on the spin wave excitations spectra

Abstract: We have investigated theoretically (with micromagnetic simulations and plane wave method) and experimentally (with ferromagnetic resonance and Brillouin light scattering) three types of antidot lattices (ADLs) based on permalloy thin films with increased complexity of the unit cell: simple square, bi-component square and wave-like ADL. We have found that placing a small additional antidot in the center of the unit cell of the square ADL modify significantly the spin wave spectrum and its dependence on the orientation of the in-plane magnetic field. We also check the further changes of spin wave spectrum resulting from the introduction of air-gaps connecting small and large antidots. In particular, the presence of small antidots change the dependence of the frequency of the fundamental mode on the angle of the in-plane applied magnetic field. The air-gaps strongly discriminates the propagation of spin waves in two principal direction of ADL lattice, orthogonal to each other. In spite of these spectral changes, the spatial distribution of the spin wave amplitude generally preserves some similarities for all three structures. We also highlighted out the role of defects in the ADL in the observed spectra. The obtained results can be interesting for the magnonics applications of the magnonic crystals.

Polarized neutron reflectivity and X-ray scattering measurements as tools to study properties of Pt/Co/Pt ultrathin layers irradiated by femtosecond laser pulses

Abstract: We have used polarized neutron reflectivity, X-ray diffraction, X-ray reflectivity and magneto-optical Kerr effect in polar configuration to study the properties of ultrathin Pt/Co/Pt films. Structures consisting of a 5-nm thick Pt buffer, 3-nm thick Co layer and 5-nm thick Pt cover layer were deposited onto (0001)-oriented Al2O3 substrate by the molecular beam epitaxy (MBE) method. Irreversible modifications of film properties, resulting from its illumination by single femtosecond laser pulses, of duration of 40 fs and wavelength of 800 nm, were observed and analyzed. As prepared films exhibited magnetization in-plane, but after laser irradiation, the direction of magnetization was rotated to out-of-plane state. Formation of Co–Pt alloy phase caused by quasi-uniform film irradiation was demonstrated by the results of X-ray and neutron scattering measurements. Moreover, polarized neutron and X-ray reflectivity data showed that after illumination Co was distributed mostly in the area of nominal Co ...

Anisotropy of magnetooptical response of nanoperforated permalloy films

Abstract: The azimuthal anisotropy of the linear and nonlinear magnetooptical Kerr effect has been studied for a structure that is an ordered array with 420-nm-diameter pores in a 30-nm-thick permalloy film on a silicon substrate. The azimuthal anisotropy of the magnetooptical Kerr effect and the coercive force, corresponding to 4 m symmetry of a planar nanopore array, has been established experimentally. The measurements are accompanied with the numerical calculation of the anisotropic magnetization distribution in the structure at different orientations of the applied magnetic field.