The bioceramics, hydroxyapatite (HAP), is a material which is biocompatible to the human body and is well suited to be used in hyperthermia applications for the treatment of bone cancer. We investigate the substitution of iron and manganese into the hydroxyapatite to yield ceramics having the empirical formula Ca9.4Fe0.4Mn0.2(PO4)(6)(OH)(2). The samples were prepared by the co-precipitation method. The formation of the nanocrystallites in the HAP structure as the heating temperatures were raised to obtain a glass-ceramic system are confirmed by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED) and electron spin resonance (ESR). TEM images show the core/shell structure of the nanoparticles, with the core being formed by the ferrites and the shell by the hydroxyapatite. The ED patterns indicate the nanoparticles formed at 500 degrees C have an amorphous structure while the nanoparticles formed at 1000 degrees C are crystalline. ESR. spectroscopy indicated that the Fe3+ ions have a g-factor of 4.23 and the Mn2+ ions have a g-factor of 2.01. The values of the parameters in the spin Hamiltonian which describes the interaction between the transition metal ions and the Ca2+ ions, indicate that the Mn2+ ion substitute into the Ca2+ sites which are ninefold coordinated, i,e., the Ca(l) sites. (c) 2007 Elsevier Ltd. All rights reserved.