Synthesis and magnetic properties of PVP coated copper-chromium hexacyanide nanoparticles

Abstract

Nanoparticles of copper chromium hexacyanide with varying particle-size are prepared by the micro-emulsion method using Poly(vinylpyrrolidone)(PVP) as a protecting polymer. The particle size (diameter: 23 – 6 nm) is varied by changing the mixing ratios of PVP to copper ion concentration from 20 to 200. The nanoparticles crystallize in a face centred cubic structure with Fm3m space group. Interestingly, these nanoparticles show significantly enhanced saturation magnetization with decreasing particle size (approx 51% over a size variation of 17 nm). Spontaneous magnetization at 1.5 K is also found to increase from 18.6 emu/g to 42.5 emu/g with decreasing particle size from 23 nm to 6 nm for these ferromagnetic nanoparticles. The observed magnetic properties of the nanoparticles have been ascribed to a possible charge transfer transition from Cu+ (S = 0)-NC-Cr4+ (S = 1) state to Cu2+ (S = 1/2)-NC- Cr3+ (S = 3/2) state, which explains the increase in the magnetization with decreasing particle size.