Poly(methyl methacrylate) Coating of Soft Magnetic Amorphous and Crystalline Fe,Co-B Nanoparticles by Chemical Reduction

The structural and magnetic properties of a collection of nanoparticles coated by Poly(methylmethacrylate) through a wet chemical synthesis have been investigated. The particles display eitheran amorphous (M=Fe, Co) M-B arrangement or a mixed structure bcc-Fe and fcc-Co+amorphous M–B. Both show the presence of a metal oxi-hydroxide formed in aqueous reduction. The organiccoating facilitates technological handling. The cost-effective synthesis involves a reduction in aPoly(methyl methacrylate) aqueous solution of iron(II) or cobalt(II) sulphates (<0.5 M) by sodiumborohydride (<0.5 M). The particles present an oxidized component, as deduced from X-ray diffraction, Mössbauer and Fe- and Co K-edge X-ray absorption spectroscopy and electron microscopy.For the ferrous alloys, this Fe-oxide is α-goethite, favoured by the aqueous solution. The Poly(methylmethacrylate) coating is confirmed by Fourier transform infrared spectroscopy. In pure amorphouscore alloys there is a drastic change of the coercivity from bulk to around 30 Oe in the nanoparticles.The mixed structured alloys also lie in the soft magnetic regime. Magnetisation values at roomtemperature range around 100 emu/g. The coercivity stems from multidomain particles and theiragglomeration, triggering the dipolar interactions.