Half-Metallic Ferromagnetism in Double Perovskite Ca2CoMoO6 Compound : DFT + U Calculations

A systematic investigation on magnetism and spin-resolved electronic properties in double perovskite Ca2CoMoO6 compound was performed by using the full-potential augmented plane wave plus local orbitals (APW+lo) method within the generalized gradient approximation (GGA-PBE) and GGA-PBE+U scheme. The stability of monoclinic phase (P2114) relative to the tetragonal (I487) and cubic (Fmm 225) phase is evaluated. We investigate the effect of Hubbard parameter Uon the ground-state structural and electronic properties of Ca2CoMoO6 compound. We found that the ferromagnetic ground state is the most stable magnetic configuration. The calculated spin-polarized band structures and densities of states indicate that the Ca2CoMoO6 compound is half-metallic (HM) and half-semiconductor (HSC) ferromagnetic (FM) semiconductor with a total magnetic moment of 6.0 using GGA-PBE and GGA-PBE+U, respectively. The Hubbard U parameter provides better description of the electronic structure. Using the Vampire code, an estimation of exchange couplings and magnetic Curie temperature is calculated. Further, our results regarding the magnetic properties of this compound reveal their ferromagnetic nature. The GGA-PBE+U approach provides better band gap results as compared to GGA-PBE approximation. These results imply that Ca2CoMoO6 could be a promising magnetic semiconductor for application in spintronic devices

Validation of 15 kGy as a radiation sterilisation dose for bone allografts manufactured at the Queensland Bone Bank: application of the VDmax 15 method

BACKGROUND: ISO 11137-2006 (ISO 11137-2a 2006) provides a VDmax 15 method for substantiation of 15 kGy as radiation sterilisation dose (RSD) for health care products with a relatively low sample requirement. Moreover, the method is also valid for products in which the bioburden level is less than or equal to 1.5. In the literature, the bioburden level of processed bone allografts is extremely low. Similarly, the Queensland Bone Bank (QBB) usually recovers no viable organisms from processed bone allografts. Because bone allografts are treated as a type of health care product, the aim of this research was to substantiate 15 kGy as a RSD for frozen bone allografts at the QBB using method VDmax 15-ISO 11137-2: 2006 (ISO 11137-2e, Procedure for method VDmax 15 for multiple production batches. Sterilisation of health care products - radiation - part 2: establishing the sterilisation dose, 2006; ISO 11137-2f, Procedure for method VDmax 15 for a single production batch. Sterilisation of health care products - radiation - part 2: establishing the sterilisation dose, 2006). MATERIALS: 30 femoral heads, 40 milled bone allografts and 40 structural bone allografts manufactured according to QBB standard operating procedures were used. METHOD: Estimated bioburdens for each bone allograft group were used to calculate the verification doses. Next, 10 samples per group were irradiated at the verification dose, sterility was tested and the number of positive tests of sterility recorded. If the number of positive samples was no more than 1, from the 10 tests carried out in each group, the verification was accepted and 15 kGy was substantiated as RSD for those bone allografts. RESULTS: The bioburdens in all three groups were 0, and therefore the verification doses were 0 kGy. Sterility tests of femoral heads and milled bones were all negative (no contamination), and there was one positive test of sterility in the structural bone allograft. Accordingly, the verification was accepted. CONCLUSION: Using the ISO validated protocol, VDmax 15, 15 kGy was substantiated as RSD for frozen bone allografts manufactured at the QBB