Magnetic colloid by PLA: Optical, magnetic and thermal transport properties

•Synthesis of ferrofluid of Co and cobalt oxide NPs by LP-PLA.•Proposed a possible laser ablation mechanism in liquid and formation of NPs.•Band gap engineering of Cobalt oxide ferrofluids using different laser pulse energy.•Coercivity of pure cobalt NPs in ethanol is smaller than that of cobalt oxide NPs in DDW.•Enhancement in thermal conductivity at room temperature on increasing laser pulse energy. Ferrofluids of cobalt and cobalt oxide nanoparticles (NPs) have been successfully synthesized using liquid phase-pulse laser ablation (LP-PLA) in ethanol and double distilled water, respectively. The mechanism of laser ablation in liquid media and formation process for Co target in double distilled water (DDW) and ethanol are speculated based on the reactions between laser generated highly nascent cobalt species and vaporized solvent media in a confined high temperature and pressure at the plume-surrounding liquid interface region. Optical absorption, emission, vibrational and rotational properties have been investigated using UV–vis absorption, photoluminescence (PL) and Fourier transform-infra red (FT-IR) spectroscopy, respectively. In this study optical band gap of cobalt oxide ferrofluids has been engineered using different pulse energy of Nd:YAG laser in the range of (2.80–3.60eV). Vibrating sample magnetometer (VSM) is employed to determine the magnetic properties of ferrofluids of cobalt and cobalt oxide NPs while their thermal conductivities are examined using rotating disc method. Ferrofluids have gained enormous curiosity due to many technological applications, i.e. drug delivery, coolant and heating purposes.