[en] We have studied a series of nanostructured ZnFe_2O_4 samples produced by mechanical milling by neutron diffuse scattering, over the temperature range (1.5–295 K). In this study we have used polarization analysis to unambiguously differentiate between atomic and magnetic contributions. From the magnetic neutron diffraction we deduce that our samples possess tetragonal antiferromagnetic symmetry corresponding to the magnetic space group I_c222. The best fit between the magnetic model and data is where moments lie in the basal plane. It is known that inversion between Zn on the A sites and Fe on the B sites of the AB_2O_4 lattice increases systematically with increased milling (as particle size decreases), leading to marked changes in the magnetic correlations. Consistent with earlier reports on Zinc Ferrites, we find that the long range magnetic order (which appears below T_N~10 K) gradually transitions from antiferromagnetic to ferrimagnetic with decreasing particle size and we have determined the relative strength of these two components. In addition we observe a marked increase in magnetic short range order above T_N. We have modeled this assuming participation only of B-site Fe atoms and find that the correlations are antiferromagnetic in nature and extend out to a distance of 9 Å. We are working on an interpretation of the change in magnetic properties from bulk to nano-particulate Zinc Ferrite through combination of crystallographic and microstructural factors based on a model with distinct core and shell contributions.

[en] Full text: The ability to design materials with preferred structural and magnetic properties in a controlled manner is important both to gain complete understanding of systems and to develop materials with enhanced physical properties. We have investigated PrMn₂Ge_2xSix compounds with x=0.4, 1.0, 1.2 and 1.6 by x-ray diffraction, magnetic, differential scanning calorimetry and neutron diffraction measurements over the temperature range ³-480^_K. Substitution of Ge with Si leads to contraction of the unit cell and associated changes in the magnetic states. Compounds with low and high levels of Si content follow the behaviour of the end products PrMn₂Ge₂ and PrMn₂Si₂. PrMn₂Ge₁.6_Sio.4 has four magnetic phase transitions (∼ ⁴28^K, ∼ ³25^K, ∼ ¹67^K, ∼⁵1^K) similar to PrMn₂Ge₂ - with PrMn₂Ge0.4Si₁.₆ exhibiting two magnetic phase transitions ∼ ³71^K and ∼ ³35^K - similar to PrMn₂Si₂. By comparison, both PrMn₂Ge₁.o_Si₁._o and PrMn₂Ge_o.₈Si₁.₂ show re-entrant ferromagnetic behaviour as the structural and magnetic interplay takes place on replacement of Ge with Si. Refinements of the neutron diffraction patterns have provided detailed insight to the magnetic structures of all samples. Full details of these controlled transformations along with evidence for coexistence of canted ferromagnetic F_mc and canted antiferromagnetic AF_mc for PrMn₂Ge_2xSix with x=1.0 and 1.2 will be presented.

[en] Highlights: • Facilesynthesis of inorganic Bi(OH)₃ nanoparticles. • High biocompatibility in human skin and dog kidney cells in vitro. • Ultraviolet filter capable of reducing the photocatalytic activity of TiO₂ and ZnO. • Preparation of TiO₂/Bi(OH)₃ and classical TiO₂/ZnO sunscreen formulations. • Significantly improved photoprotection and photostability compared to TiO₂/ZnO. - Abstract: In this study we investigate readily synthesised Bi(OH)₃ nanoparticles as a novel, multifunctional ultraviolet filter for sunscreen. The absorbance of Bi(OH)₃ NPs in the ultraviolet region is comparable to that of both ZnO and TiO₂ NPs used in commercial sunscreens. In vitro photoprotection results show that the combination of TiO₂/Bi(OH)₃ is more efficient than TiO₂/ZnO over the whole UV range, with an increase in sun protection factor of 28%. The emulsions show rheological properties comparable to those of commercial sunscreens. The combination of TiO₂/Bi(OH)₃ led to insignificant damage on pre-painted steel panels after exterior exposure for twelve weeks. We also demonstrate that the addition of Bi(OH)₃ NPs reduces the degradation of crystal violet by photocatalytically active TiO₂ or ZnO NPs under ultraviolet exposure. Finally, assessment of the biocompatibility of Bi(OH)₃ with HaCaT keratinocytes and Madin-Darby Canine Kidney (MDCK) cells in vitro is described.