High-temperature ferromagnetism in Co-doped CeO2 synthesized by the coprecipitation technique.

The aim of the present study is to check the influence of annealing under vacuum and a mixture of N(2)-H(2) atmosphere on the magnetic properties of polycrystalline Co-doped CeO(2) diluted magnetic oxides (DMOs) with Co concentrations of 5 at% synthesized using the coprecipitation technique. X-Ray diffraction (XRD) patterns and transmission electron microscopy (TEM) showed for all samples the expected CeO(2) cubic fluorite-type structure and that Co ions are uniformly distributed inside the samples. Room-temperature Raman and photoluminescence (PL) spectroscopies indicate an increase in the concentration of oxygen vacancies upon Co doping and further annealing. Field dependent magnetization measurements revealed a paramagnetic behavior for as-prepared Co-doped CeO(2), while a ferromagnetic behavior appears when the same samples are annealed under vacuum or N(2)-H(2) atmosphere. Temperature dependent magnetization measurements suggest that the observed ferromagnetism is due to the presence of metallic Co clusters with nanometric size and broad size distribution. These results are supported by electron paramagnetic resonance studies.

Co and Al co-doping for ferromagnetism in ZnO:Co diluted magnetic semiconductors.

Co and Al co-doped ZnO diluted magnetic semiconductors are fabricated by a pulsed laser deposition and their electronic structure is investigated using x-ray absorption and emission spectroscopy. The Zn(0.895)Co(0.100)Al(0.005)O thin films grown under oxygen-rich conditions exhibit ferromagnetic behavior without any indication of Co clustering. The Co L-edge and O K-edge x-ray absorption and emission spectra suggest that most of the Co dopants occupy the substitutional sites and the oxygen vacancies are not responsible for free charge carriers. The spectroscopic results and first principles calculations reveal that the ferromagnetism in Co and Al co-doped ZnO semiconductors mainly arises from Al interstitial defects and their hybridization with Co substitutional dopants.

How to obtain a magnetic hard-soft architecture by pulsed laser deposition.

In spin valve type systems, one ferromagnetic electrode must be magnetically hard to act as a reference layer while the other electrode must be magnetically soft to act as a sensor or storage layer. This magnetic hard-soft architecture can usually be obtained by four different methods: the use of two ferromagnets with different coercive fields (here CoFe(2) and Ni(80)Fe(20)), the use of an underlayer enhancing the coercive field of one of the two ferromagnets (here Ta and Ru), the use of a ferromagnet coupled to a ferrimagnet or antiferromagnet (here NiO/CoFe(2) and CoFe(2)O(4)/CoFe(2)), or the use of an artificial antiferromagnet (here CoFe(2)/Ru/CoFe(2)). We show that at least the first and the third methods seem to work with pulsed laser deposition in the thermodynamic conditions used.