Composite materials containing amorphous iron embedded in poly(methylacrylate) or poly(methylmethacrylate) and amorphous cobalt embedded in poly(methylacrylate) were formed using a sonochemical method. The physical and thermal properties of the composite materials were probed. A significant difference in the solubility of the iron–poly(methylacrylate) and cobalt–poly(methylacrylate) in various solvents was observed. This difference is accounted for by the stronger interaction existing between the cobalt and the surrounding polymer. For iron–poly(methylacrylate) this interaction is weakened due to the formation of an iron complex.