Ferromagnetic nickel filled in borate shell by controlled oxidation-crystallization of boride in air

A model design of protected nanoparticles (NPs) of a ferromagnetic metal such as nickel by using a surface layer of borate make them safer in view of human health and environments. Here we report a simple method of producing one-dimensional ferromagnetic nanostructure (1D-FMN) of Ni-NPs impregnated in stable borate shell by controlled oxidation of a nickel boride in air. Ni-filled nanostructure, ∼100 nm diameter and ∼1.5 μm length, have transformed out of a surface limited oxidation of a nickel boride (NPs) at ∼800 °C in air. An antioxidant borate prevents the residual nickel from oxidizing further unless the temperature rises above 800 °C. Result is useful for understanding growth mechanism of 1D-FMN in support with inherited oxide of low-melting-point. A borate assisted 1D-FMN so obtained yields superior magnetic properties, i.e., Ms = 29.0 emu/g, Hc = 236 Oe and remenance ∼0.3 at room temperature, in comparison to mostly 1D-FMN reported using a carbon layer. © 2014 Elsevier B.V. All rights reserved.