Franklin Massami Matinaga

A deeper understanding of magnetic systems exhibiting perpendicular magnetic anisotropy (PMA), including magnetic multilayers, intermetallic compounds, and alloys, has attracted attention owing to their broad technological applications, particularly in magnetic data storage devices. Among available experimental approaches, magneto-optical techniques, particularly the magneto-optical Kerr effect (MOKE), have proven powerful and widely used for investigating magnetic materials. In this work, we proposed a high-resolution optical alignment protocol and an analytical-instrumental analyzer-angle-resolved magnetometry methodology, based on the Jones formalism, to extract Kerr rotation angles from measurements on PMA samples. The optimization of the polar MOKE (p-MOKE) response from fractional MOKE signals is discussed, and characterization of asymmetric hysteresis loops associated with different magnetic states along magnetization-reversal dynamics. The proposed methodology enables the determination of the Kerr rotation angle, fractional MOKE signal optimization, and analysis of magnetic-state-dependent hysteresis behavior. We obtained good agreement between the theoretical model and experimental measurements. Overall, the discussed methodology provides enhanced analytical capabilities and access to a broader range of parameters for the study of magnetic systems exhibiting PMA compared with which is typically exploited. As case studies, the presented approach is applied to two magnetic systems: [Co60Fe40/Pt]5 multilayer and MnGaGe thin film.

Femtosecond time-resolved spin and phonon wave dynamics were investigated in CoFe/Pt multilayers. Besides the spin and phonon dynamics simultaneous analysis, the high resolution and bandwidth (up to THz) of our approach allowed to estimate magnon’s group velocity and the dynamic exchange coefficient Aex of these magnetic CoFe/Pt multilayers.

Researching optical effects in nanowires may require a high pump intensity which under ambient conditions can degrade nanowires due to thermal oxidation. In this work we investigated the photodegradation of a single Si-doped GaAs nanowire by laser heating in air. To understand the changes that occurred on the nanowire we carried out Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and photoluminescence spectroscopy in laser damaged regions as well as in non-affected ones. From Raman Stokes and anti-Stokes measurements we estimated the local temperature that the oxidation process of the nanowire (NW) surface starts at as 661 K, resulting in two new Raman modes at 200 cm⁻¹ and 259 cm⁻¹. Scanning electron microscopy and energy dispersive X-ray spectroscopy measurements showed a significant loss of arsenic in the oxidized regions, but no erosion of the nanowire. Micro-photoluminescence measurements showed the near-band-edge emission of GaAs along the nanowire, as well as a new emission band at 755 nm corresponding to polycrystalline β-Ga₂O₃ formation. Our results also indicate that neither amorphous As nor crystalline As were deposited on the surface of the nanowire. Combining different experimental techniques, this study showed the formation of polycrystalline β-Ga₂O₃ by oxidation of the nanowire surface and the limits for performing spectroscopic investigations on individual GaAs NWs under ambient air conditions.

Faraday rotation (FR) can also be observed in a resonantly excited system without an external magnetic field. In a microcavity, polaritons spin population imbalance generates an effective magnetic field across the cavity mode, which results in an amplified FR on the emitted photon. Also, when the cavity is tuned to light hole (LH) exciton energy, an additional field momentum will be added to the effective magnetic field parallel to cavity mode, resulting in a aditional FR.

Neste trabalho realizamos o estudo da cinética e formação de agregados em cristais iônicos halogenetos alcalinos dopados com impurezas divalentes, através da técnica de espectroscopia de absorção de dois...