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Femtosecond laser-pulse excitation provides an energy efficient and fast way to control magnetization at the nanoscale, providing great potential for ultrafast next-generation data manipulation and nonvolatile storage devices. Ferromagnetic van der Waals materials have garnered much attention over the past few years due to their low dimensionality, excellent magnetic properties, and large response to external stimuli. Nonetheless, their behaviour upon fs laser-pulse excitation remains largely unexplored. Here, we investigate the ultrafast magnetization dynamics of a thin flake of Fe$_3$GeTe$_2$ (FGT) and extract its intrinsic magnetic properties using a microscopic framework. We find that our data is well described by our modelling, with FGT undergoing a slow two-step demagnetization, and we experimentally extract the spin-relaxation timescale as a function of temperature, magnetic field and excitation fluence. Our observations indicate a large spin-flip probability in agreement with a theoretically expected large spin-orbit coupling, as well as a weak interlayer exchange coupling. The spin-flip probability is found to increase when the magnetization is pulled away from its quantization axis, opening doors to an external control over the spins in this material. Our results provide a deeper understanding of the dynamics van der Waals materials upon fs laser-pulse excitation, paving the way towards two-dimensional materials-based ultrafast spintronics., Supplementary information included

Protecting our natural resources is one of the important thrusts of every organization. In this study, the waters of Iloilo Batiano River, Philippines is explored. This study was conducted because there is a dearth of information on the water physico-chemical characteristics of the river. Since this is an initial assessment, this study will serve as a baseline data and the results will serve as a basis for future reference for conservation measures of the river. The present study aimed to determine the selected water physico-chemical characteristics of the river such as the electrical conductivity (EC), temperature, pH, and calcium content; assess if these parameters exceed the limit set by the DENR Administrative Order No. 20F16-08 of the Republic of the Philippines and other available literatures; and to determine if there was no significant difference in the water physico-chemical characteristics among the six sampling stations. Results revealed that EC and calcium content of the river exceed their limits except for temperature and pH levels. Furthermore, EC and temperature were statistically different among the six sampling stations except for pH values. This study concludes that the river is saline due to the mixing of saltwater and surface water as the river is near to the sea and has high calcium content that can threaten the life of freshwater aquatic organisms.

Large skyrmion bubbles in confined geometries of various sizes and shapes are investigated, typically in the range of several micrometers. Two fundamentally different cases are studied to address the role of dipole-dipole interactions: (I) when there is no magnetic material present outside the small geometries and (II) when the geometries are embedded in films with a uniform magnetization. It is found that the preferential position of the skyrmion bubbles can be controlled by the geometrical shape, which turns out to be a stronger influence than local variations in material parameters. In addition, independent switching of the direction of the magnetization outside the small geometries can be used to further manipulate these preferential positions, in particular with respect to the edges. We show by numerical calculations that the observed interactions between the skyrmion bubbles and structure edge, including the overall positioning of the bubbles, can be explained by considering only dipole-dipole interactions.