Bioceramics are versatile materials for hard tissue engineering. Hydroxyapatite (HA) is a widely studied biomaterial for bone grafting and tissue engineering applications. The crystal structure of HA allows for a wide range of substitutions, which allows for tailoring materials properties. Transition metals and lanthanides are of interest since substitution in HA can result in magnetic properties. In this study, experimental results were compared to theoretical calculations of HA substituted with a transition metal. Calculation of a 10 atomic percent substitution of a transition metal ion Mn(2+), Fe(2+), and Co(2+) substituted HA samples lead to magnetic moments of 5, 4, and 3 Bohr magnetons, respectively. Hydroxyapatite substituted by transition metals (MHA) was fabricated through an ion exchange procedure and characterized with X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), X-ray photoelectron spectroscopy, and vibrating sample magnetometer, and results were compared to theoretical calculations. All the substitutions resulted in phase-pure M(2+)HA with lattice parameters and FTIR spectra in good agreement with calculations. Magnetic measurements revealed that the substitution of Mn(2+) has the greatest effect on the magnetic properties of HA followed by the substitution of Fe(2+) and then Co(2+). The present work underlines the power of synergistic theoretical-experimental work in guiding the rational design of materials.

Effects of the substitution of rare-earths R = Y, Er, and Ho on the magnetic properties of Dy 0.7 R 0.3 CrO 3 are reported here in order to probe the nature of magnetism and related exchange interactions in these materials. By fitting the temperature dependence of the magnetic susceptibility to a modified Curie-Weiss law, which includes a correction for the Dzyaloshinskii-Moriya (DM) interaction, the strengths of the symmetric and antisymmetric Cr 3+-Cr 3+ exchange interactions were determined. It was found that the rare-earth substitutions had a slight effect on the strength of the symmetric Cr 3+-Cr 3+ interaction (reflected in the slight changes in the Néel temperatures) while the antisymmetric Cr 3+-Cr 3+ interaction remained unchanged. Isothermal magnetic measurements of the samples at successive temperatures revealed a plateau in the temperature dependent magnetic coercivity data, which was explained by the magnetic properties of the substituted ions. It was found that the Y substitution lead to the reduction of the strength of the magnetization and a larger peak value of magnetic coercivity as compared to that in pure DyCrO 3. The observed increase in coercivity with Er and Ho substitution can be attributed to an increased R 3+-Cr 3+ interaction strength dominated by the DM mechanism.

No abstract

In this work, a polycrystalline bulk DyCrO 3 sample was prepared by a solution route and the structural and magnetic properties were investigated. The phase purity and ionic valence state of the DyCrO 3 sample were determined by x-ray diffraction/Raman spectroscopy and x-ray photoelectron spectroscopy, respectively. The AC and DC magnetization measurements revealed the onset of antiferromagnetic order at 146 K with an effective moment of 8.88 l B . Isothermal magnetization measurements of this material are presented for the first time, showing a peak in the coercive field at 80 K that is explained by the competition between the paramagnetic Dy 3þ and Cr 3þ sublattices. DyCrO 3 was found to display a large magnetocaloric effect (8.4 J/kg K) and relative cooling power (217 J/kg) at 4 T applied field, which renders DyCrO 3 useful for magnetic refrigeration between 5 K and 30 K. V C 2013 AIP Publishing LLC. [http://dx.

Pure and Fe-doped HoCrO3 and DyCrO3 powders were examined for the magnetocaloric properties with promising relative cooling power (RCP) values indicating their potential for applications in magnetic refrigeration.