Graphical contents entryMesoporous NiO/NiCo2O4/Co3O4 composites showing variable degrees of order and tunable magnetic properties are achievable by nanocasting using SBA-15 silica as hard templates. The -2 -NiCo2O4-rich powders are magnetic at room temperature and can be easily remotely manipulated using small fields (see Fig.).-3 -A series of mesoporous NiO/NiCo2O4/Co3O4 composites has been synthesized by nanocasting using SBA-15 silica as a hard template. The evaporation method was used as the impregnation step. Nickel and cobalt nitrates in different Ni(II):Co(II) molar ratios were dissolved in ethanol and used as precursors. The composites show variable degrees of order, from randomly organized nanorods to highly ordered hexagonally-packed nanowires as the Ni(II):Co(II) molar ratio decreases. The materials exhibit moderately large surface areas, in the 60-80 m 2 /g range. Their magnetic properties, saturation magnetization (MS) and coercivity (HC), can be easily tuned given the ferrimagnetic (NiCo2O4) and antiferromagnetic (NiO and Co3O4) character of the constituents. Moreover, the NiCo2O4 rich materials are magnetic at room temperature and can consequently be easily manipulated by small magnets. Owing to their appealing combination of properties, the nanocomposites are expected to be attractive for myriad applications.

Mesoporous NiCo 2 O 4 spinel has been synthesized by nanocasting, using SBA-15 and KIT-6 silica as hard templates. Two temperatures of calcination were applied for the conversion of the spinel precursors (metal nitrates) into NiCo 2 O 4 . At 375°C the pure spinel was obtained, whereas at 550°C NiO impurities were detected. The mesoporous powders obtained were characterized by transmission electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, and magnetic measurements. In addition, their thermal stability was assessed by post heat-treating the materials at 550°C: the mesostructure of the pure spinel (calcined at 375°C) collapsed, leading to the disruption of the porous network, while the mesoporosity of the powders calcined at 550°C was preserved. In all cases, the post-thermal treatment induced the segregation of NiO; the final NiO amount was found to be in the 7-10 wt % range.

Transition metal (Co, Fe, Mn)‐doped In2O3−y mesoporous oxides are synthesized by nanocasting using mesoporous silica as hard templates. 3D ordered mesoporous replicas are obtained after silica removal in the case of the In‐Co and In‐Fe oxide powders. During the conversion of metal nitrates into the target mixed oxides, Co, Fe, and Mn ions enter the lattice of the In2O3 bixbyite phase via isovalent or heterovalent cation substitution, leading to a reduction in the cell parameter. In turn, non‐negligible amounts of oxygen vacancies are also present, as evidenced from Rietveld refinements of the X‐ray diffraction patterns. In addition to (In1−xTMx)2O3−y, minor amounts of Co3O4, α‐Fe2O3, and MnxOy phases are also detected, which originate from the remaining TM cations not forming part of the bixbyite lattice. The resulting TM‐doped In2O3−y mesoporous materials show a ferromagnetic response at room temperature, superimposed on a paramagnetic background. Conversely, undoped In2O3−y exhibits a mixed diamagnetic‐ferromagnetic behavior with much smaller magnetization. The influence of the oxygen vacancies and the doping elements on the magnetic properties of these materials is discussed. Due to their 3D mesostructural geometrical arrangement and their room‐temperature ferromagnetic behavior, mesoporous oxide‐diluted magnetic semiconductors may become smart materials for the implementation of advanced components in spintronic nanodevices.

Electron tomography is a widely spread technique for recovering the three dimensional (3D) shape of nanostructured materials. Using a spectroscopic signal to achieve a reconstruction adds a fourth chemical dimension to the 3D structure. Up to date, energy filtering of the images in the transmission electron microscope (EFTEM) is the usual spectroscopic method even if most of the information in the spectrum is lost. Unlike EFTEM tomography, the use of electron energy-loss spectroscopy (EELS) spectrum images (SI) for tomographic reconstruction retains all chemical information, and the possibilities of this new approach still remain to be fully exploited. In this article we prove the feasibility of EEL spectroscopic tomography at low voltages (80 kV) and short acquisition times from data acquired using an aberration corrected instrument and data treatment by Multivariate Analysis (MVA), applied to Fe(x)Co((3-x))O(4)@Co(3)O(4) mesoporous materials. This approach provides a new scope into materials; the recovery of full EELS signal in 3D.

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