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Articles you may be interested inMicrostructure and magnetic properties of MFe2O4 (M = Co, Ni, and Mn) ferrite nanocrystals prepared using colloid mill and hydrothermal method J. Appl. Phys. 117, 17A328 (2015) We report by the first time a high pressure X-ray diffraction and Raman spectroscopy study of cobalt ferrite (CoFe 2 O 4 ) nanoparticles carried out at room temperature up to 17 GPa. In contrast with previous studies of nanoparticles, which proposed the transition pressure to be reduced from 20-27 GPa to 7.5-12.5 GPa (depending on particle size), we found that cobalt ferrite nanoparticles remain in the spinel structure up to the highest pressure covered by our experiments. In addition, we report the pressure dependence of the unit-cell parameter and Raman modes of the studied sample. We found that under quasi-hydrostatic conditions, the bulk modulus of the nanoparticles (B 0 ¼ 204 GPa) is considerably larger than the value previously reported for bulk CoFe 2 O 4 (B 0 ¼ 172 GPa). In addition, when the pressure medium becomes non-hydrostatic and deviatoric stresses affect the experiments, there is a noticeable decrease of the compressibility of the studied sample (B 0 ¼ 284 GPa). After decompression, the cobalt ferrite lattice parameter does not revert to its initial value, evidencing a unit cell contraction after pressure was removed. Finally, Raman spectroscopy provides information on the pressure dependence of all Raman-active modes and evidences that cation inversion is enhanced by pressure under non-hydrostatic conditions, being this effect not fully reversible. V C 2015 AIP Publishing LLC. [http://dx

In this work, we present an experimental and theoretical study of structural and magnetic properties of Fe doped rutile TiO2 nanopowders. We show that Fe-doping induces the formation of oxygen vacancies in the first-sphere coordination of iron ions, which are in +2 and +3 oxidation states. We found that Fe ions form dimers that share one oxygen vacancy in the case of Fe3+ and two oxygen vacancies in the case of Fe2+. The saturation magnetization is almost independent of iron concentration and slightly increases with the relative fraction of Fe2+. Ab initio calculations show that two Fe ions sharing an oxygen vacancy are coupled ferromagnetically, forming a bound magnetic polaron (BMP), but two neighbor BMPs are aligned antiparallel to each other. Extra electron doping plays a fundamental role mediating the magnetic coupling between the ferromagnetic entities: carriers, possibly concentrated at grain boundaries, mediate between the BMP to produce ferromagnetic alignment.