Javier Curiale

Reliable estimation of rare earth element concentrations in aqueous media is relevant to process control, environmental monitoring, and analytical decision-making. Here, we present a rapid and cost-effective UV-Vis spectroscopic method for estimating praseodymium (Pr), neodymium (Nd), and dysprosium (Dy) concentrations using analyte-specific spectral regions and spectrum-specific adaptive baseline modeling. Four candidate baseline models were evaluated independently for each spectrum using exclusively spectral criteria, allowing analytical signals to be extracted from narrow REE absorption bands despite variations in background shape and intensity. Method performance was assessed through calibration, limits of detection and quantification, trueness, repeatability, intermediate precision, matrix effects, and interference from Ca$^{2+}$ and Fe$^{3+}$. Pr and Nd showed the most consistent analytical performance, with linear calibration ranges of 0-750~ppm and estimated limits of quantification (LOQs) of 1.88 and 3.00~ppm, respectively. In contrast, Dy exhibited lower sensitivity and greater susceptibility to background and interference effects, with a calibration range of 0--850~ppm and an estimated LOQ of 61.59~ppm. The proposed workflow uses conventional UV-Vis instrumentation and simple computational processing to provide rapid, low-cost, screening-level concentration estimates, offering a practical approach for preliminary assessment of REE-containing aqueous samples and for supporting subsequent analytical decisions when more complex or resource-intensive elemental analysis may be required.

Magnetic imaging techniques are widespread critical tools used in fields such as magnetism, spintronics, or even superconductivity. Among them, one of the most versatile methods is the magneto-optical Kerr effect. However, as soon as light is blocked from interacting with the magnetic layer, such as in deeply buried layers, optical techniques become ineffective. In this work, we present a spin accumulation based magneto-optical Kerr effect microscopy technique that enables imaging of a magnetic thin-film covered by thick and opaque metallic layers. The technique is based on the generation and detection of transient spin accumulations that propagate through the thick metallic layer. These spin accumulation signals are directly triggered and detected optically on the same side, lifting any substrate transparency requirements. The spin accumulation signals detected on a Cu layer decay with a characteristic length of 60 nm, much longer than the 12 nm optical penetration depth, allowing for the detection of magnetic contrast with Cu capping layers up to hundreds of nm. This method should enable magnetic imaging in a wide range of experiments where the surface of interest is covered by electrodes.

We explore the contributions of adiabatic and nonadiabatic spin-transfer torques (STT) of a spin-polarized current to the thermally activated creep motion of domain walls in a thin (Ga,Mn)(As,P) film with perpendicular anisotropy. The nonadiabatic STT is found to compensate linearly an external magnetic field, with a slope compatible with a steady domain-wall internal structure. Close to the compensation, the adiabatic contribution is strongly enhanced and may both increase or reduce domain-wall velocity, which we associate to variations of creep pinning energy barrier with domain-wall internal structure. Far from compensation, the effects of adiabatic STT become negligible and so field and current driven domain-wall motion presents common universal behaviors described by the quenched Edwards Wilkinson universality class.

The dynamical response of magnetic domain walls in ultrathin magnetic films to external magnetic fields is determined not only by the composition and thickness of the layers but also by the growth conditions. Growth conditions can induce significant structural changes to the layers and at the interfaces between them, affecting in particular the dynamics of domain walls, their mobility, elastic tension, and the pinning forces acting on them. In this work, we focus specifically on the effect of Ir layer growth pressure in Ta/Pt/Co/Ir/Ta ultrathin multilayered films. Measurements of the DC magnetic properties, domain-wall velocity, and domain morphology in the creep regime for both constant and alternating field pulses were performed for a batch of samples where the Ir layer was grown at different pressures. We find that the saturation magnetization, the effective anisotropy constant, and the domain-wall surface tension grow with increasing pressure and saturate at a threshold pressure, while the Dzyaloshinskii-Moriya field and the strength of the disorder remain practically unaltered over the range of pressures considered.

Domain wall dynamics and spatial fluctuations are closely related to each other and to universal features of disordered systems. Experimentally measured roughness exponents characterizing spatial fluctuations have been reported for magnetic thin films, with values generally different from those predicted by the equilibrium, depinning, and thermal reference states. Here we study the roughness of domain walls in GdFeCo thin films over a large range of magnetic field and temperature. Our analysis is performed in the framework of a model considering length-scale crossovers between the reference states, which is shown to bridge the differences between experimental results and theoretical predictions. We also quantify the size of the depinning avalanches below the depinning field at finite temperatures.

Understanding the effect of fabrication conditions on domain wall (DW) motion in thin films with perpendicular magnetization is a mandatory issue in order to tune their properties aiming to design spintronics devices based on such phenomenon. In this context, the present work intends to show how different growth conditions may affect DW motion in the prototypical system Pt/Co/Pt. The trilayers were deposited by dc sputtering, and the parameters varied in this study were the Co thickness, the substrate roughness and the base pressure in the deposition chamber. Magneto-optical Kerr effect-based magnetometry and microscopy combined with x-ray reflectometry, atomic force microscopy and transmission electron microscopy were adopted as experimental techniques. This permitted us to elucidate the impact on the hysteresis loops and on the DW dynamics, produced by different growth conditions. As other authors, we found that Co thickness is strongly determinant for both the coercive field and the DW velocity. On the contrary, the topographic roughness of the substrate and the base pressure of the deposition chamber evidence a selective impact on the nucleation of magnetic domains and on DW propagation, respectively, providing a tool to tune these properties.