Magnetic properties of crystalline nickel and low phosphorus amorphous Ni1-xPx nanoparticles

Abstract This paper explores how synthesis parameters can affect the size, composition and crystallinity degree of the Ni 1-x P x nanoparticles and describes the process for preparing nanoparticles with tunable ferromagnetic, superparamagnetic and paramagnetic properties. Ni 1-x P x nanoparticles of different sizes, compositions and crystallinities were synthesized through microemulsion method and by variation of micellar ratio, type of reducing agent and process pH. The results of particle size analysis (PSA), transmission electron microscopy (TEM), atomic absorption spectroscopy (AAS) and X-ray diffraction (XRD) confirmed successful synthesis of Ni 1-x P x nanoparticles. While pure and crystalline nickel nanoparticles can be synthesized in the presence of hydrazine, phosphorus is doped on the structure of nanoparticles synthesized by sodium hypophosphite reducing agent. In this case, lower bath pH caused to synthesis of amorphous nanoparticles with higher phosphorous concentrations. It was shown that ferromagnetic nickel nanoparticles can be transferred to superparamagnetic ones if their particle size reduces to less than 14 nm. As well, crystalline to amorphous transition by phosphorus addition led to preparation of paramagnetic nanoparticles. Magnetic properties measurement using vibrating sample magnetometer (VSM) suggested interesting relationship between the magnetic properties and characteristics of nanoparticles. Moreover, the results indicated that synthesis method is flexible for preparation of nanoparticles with tunable magnetic properties from ferromagnetic to paramagnetic.