Structural and Magnetic Properties of Iron Oxide Nanoparticles in Shells of Hollow Microcapsules Designed for Biomedical Applications

The functional hollow biodegradable microcapsules modified with the maghemite γ-Fe2O3 nanoparticles and the hollow spherical CoFe2O4/SiO2 nanocomposites were synthesized. Mössbauer spectroscopy data reveal that the main part maghemite nanoparticles have evident superparamagnetic behavior which is retained up to room temperature. This allows directing the microcapsules by an external magnetic field, which is very important for the problem of target drug delivery. On the other hand, the hollow spherical CoFe2O4/SiO2 nanocomposites with the small size particles do not show superparamagnetic behavior, but transit from magnetic to paramagnetic state by jump-like magnetic transition of the first order. This effect is a specific property of the magnetic nanoparticles isolated by an inert material. The method of synthesis can be modified with various bioligands on the silane surface, and such materials can have great prospects for use in diagnostics and bio-separation

Low-spin S=1/2 ground state of the Cu trimers in the paper-chain compound Ba3Cu3In4O12

The magnetic ground states of the isostructural paper-chain compounds Ba 3Cu 3In 4O 12 and Ba 3Cu 3Sc 4O 12 were recently found to be ordered antiferromagnetically (AFM), while both quantum magnets reveal positive asymptotic Curie-Weiss temperatures suggestive of ferromagnetic (FM) interactions at high temperatures. Due to the AFM-FM competition the saturation magnetization in both compounds is reached already in modest magnetic fields with a nontrivial succession of two spin-flop and two spin-flip-like transitions in Ba 3Cu 3In 4O 12. We argue that the paper-chains in both compounds can be described as a system of CuI-2CuII trimers with a low-spin S=1/2 ground state which implies a nonmagnetic spin-singlet CuII dimer state and a spin-polarized CuI ion. To validate the model we performed extensive nuclear resonance-nuclear quadrupole resonance-nuclear magnetic resonance (NQR-NMR)-measurements in Ba 3Cu 3In 4O 12. Two different types of 63 ,65Cu nuclear resonance spectra were observed in the magnetically ordered state at zero external magnetic field: (i) a pure NQR spectrum in the frequency range of 24-30 MHz and (ii) a zero-field NMR spectrum in the frequency range of 50-65 MHz. This result unambiguously indicates that one of the two types of copper ions in Ba 3Cu 3In 4O 12 is in a nonmagnetic spin state below T N. It provides a unique criterion to test any theoretical model describing the ground-state spin structure in Ba 3Cu 3In 4O 12 . We attribute the pure NQR spectrum to CuII ions forming nonmagnetic spin-singlet 2CuII dimers and the zero-field NMR spectrum to spin-polarized CuI ions. Both NQR and zero-field NMR spectra point to an existence of at least two nonequivalent sets of the copper trimers, probably due to displacements of the CuI ions along the cavity in the c direction. © 2012 American Physical Society

Low-spin S=1/2 ground state of the Cu trimers in the paper-chain compound Ba3Cu3In4O12

The magnetic ground states of the isostructural paper-chain compounds Ba 3Cu 3In 4O 12 and Ba 3Cu 3Sc 4O 12 were recently found to be ordered antiferromagnetically (AFM), while both quantum magnets reveal positive asymptotic Curie-Weiss temperatures suggestive of ferromagnetic (FM) interactions at high temperatures. Due to the AFM-FM competition the saturation magnetization in both compounds is reached already in modest magnetic fields with a nontrivial succession of two spin-flop and two spin-flip-like transitions in Ba 3Cu 3In 4O 12. We argue that the paper-chains in both compounds can be described as a system of CuI-2CuII trimers with a low-spin S=1/2 ground state which implies a nonmagnetic spin-singlet CuII dimer state and a spin-polarized CuI ion. To validate the model we performed extensive nuclear resonance-nuclear quadrupole resonance-nuclear magnetic resonance (NQR-NMR)-measurements in Ba 3Cu 3In 4O 12. Two different types of 63 ,65Cu nuclear resonance spectra were observed in the magnetically ordered state at zero external magnetic field: (i) a pure NQR spectrum in the frequency range of 24-30 MHz and (ii) a zero-field NMR spectrum in the frequency range of 50-65 MHz. This result unambiguously indicates that one of the two types of copper ions in Ba 3Cu 3In 4O 12 is in a nonmagnetic spin state below T N. It provides a unique criterion to test any theoretical model describing the ground-state spin structure in Ba 3Cu 3In 4O 12 . We attribute the pure NQR spectrum to CuII ions forming nonmagnetic spin-singlet 2CuII dimers and the zero-field NMR spectrum to spin-polarized CuI ions. Both NQR and zero-field NMR spectra point to an existence of at least two nonequivalent sets of the copper trimers, probably due to displacements of the CuI ions along the cavity in the c direction. © 2012 American Physical Society