Influence of Magnetic Field and Solvent Environment on Laser-Ablated Ag and Cu-Based Nanoparticles: Optical and...

The influence of magnetic field (0.25 T) on the structural, optical, and thermal properties of Ag and Cu-based nanoparticles (NPs) synthesized by pulsed laser ablation in liquid (PLAL) was investigated in two solvent environments: deionized (DI) water and ethanol. Ablation was performed using Nd:YAG laser (532 nm, 6 ns, 1 J cm^-2, 10 Hz). Under magnetic confinement, mean particle diameters of 5-7 nm were obtained accompanied by improved X-ray diffraction (XRD) peak sharpness and localized surface plasmon resonance (LSPR) absorbance enhancements of 20%-53% relative to unconfined (0 T) conditions. These observations are consistent with enhanced plasma confinement via magnetic field which increases plasma density and promotes more uniform NP nucleation. LSPR peaks were recorded at 396 and 401 nm for Ag-NPs in DI water and ethanol, respectively; Cu-based NPs exhibited oxide interband absorption at 219 nm (DI water) and a metallic Cu plasmonic band at 582 nm (ethanol). Optical modeling using Mie-Drude-Lorentz and Maxwell-Garnett frameworks reproduced experimental peak positions within 7 nm with the magnetic field effect entering the model through experimentally measured size distributions and absorbance cross sections. Thermal modeling via the two-temperature model (TTM) predicted submelting lattice temperatures for all NP sizes at 1 J cm^-2, with the field-induced size reduction shifting smaller particles into a lower-temperature oxidation-favored regime. DI water promoted oxide-rich Ag/Ag₂O and Cu₂O/CuO phases; ethanol favored metallic Ag and core-shell Cu@Cu₂O/CuO morphologies via carbonaceous passivation. These results demonstrate that magnetic confinement during PLAL is a practical, additive-free route to controlling NP size, crystallinity, and optical response.