Magnetic field-assisted CVD offers a direct pathway to manipulate the evolution of microstructure, phase composition, and magnetic properties of the asprepared film. We report on the role of applied magnetic fields (0.5 T) during a cold-wall CVD deposition of iron oxide from [Fe III (O t Bu) 3 ] 2 leading to higher crystallinity, larger particulates, and better out-of-plane magnetic anisotropy, if compared with zero-field depositions. Whereas selective formation of homogeneous magnetite films was observed for the field-assisted process, coexistence of hematite and amorphous iron(III) oxide was confirmed under zero-field conditions. Comparison of the coercive field (11 vs 60 mT) indicated lower defect concentration for the field-assisted process with nearly superparamagnetic behavior. X-ray photoemission electron microscopy (X-PEEM) in absorption mode at the O-K and Fe-L 3,2 edges confirmed the selective formation of magnetite (field-assisted) and hematite (zero-field) with coexisting amorphous phases, respectively, emphasizing the importance of field−matter interactions in the phase-selective synthesis of magnetic thin films.

Chemical vapor deposition of iron pentacarbonyl (Fe(CO) 5 ) in an external magnetic field (B ¼ 1.00 T) was found to significantly affect the microstructure and anisotropy of as-deposited iron crystallites that could be transformed into anisotropic hematite (a-Fe 2 O 3 ) nanorods by aerobic oxidation. The deterministic influence of external magnetic fields on CVD deposits was found to be substrateindependent as demonstrated by the growth of anisotropic a-Fe columns on FTO (F:SnO 2 ) and Si (100), whereas the films deposited in the absence of the magnetic field were constituted by isotropic grains.TEM images revealed gradual increase in average crystallite size in correlation to the increasing field strength and orientation, which indicates the potential of magnetic field-assisted chemical vapor deposition (mfCVD) in controlling the texture of the CVD grown thin films. Given the facet-dependent activity of hematite in forming surface-oxygenated intermediates, exposure of crystalline facets and planes with high atomic density and electron mobilities is crucial for oxygen evolution reactions. The field-induced anisotropy in iron nanocolumns acting as templates for growing textured hematite pillars resulted in two-fold higher photoelectrochemical efficiency for hematite films grown under external magnetic fields (J ¼ 0.050 mA cm À2 ), when compared to films grown in zero field (J ¼ 0.027 mA cm À2 ). The dark current measurements indicated faster surface kinetics as the origin of the increased catalytic activity.

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The ferromagnetic Mn–Al–C τ‐phase ( tetragonal structure) shows intrinsic potential to be developed as a permanent magnet; however, this phase is metastable and is easily decomposed to nonmagnetic stable phases, affecting negatively the magnetic properties. Giving the necessity to careful control of its synthesis, the use of a novel approach is investigated using electric current–assisted annealing to obtain pure τ‐phase samples. The temperature and electrical resistance of the samples are monitored during annealing and it is shown that the change in resistance can be used to probe the phase transformation. Upon increase of electric current density, the required temperature for the ferromagnetic phase formation is reduced, reaching a maximum shift of 140 °C at 45 A mm−2. Even though this noticeable shift is achieved, the magnetic properties are not affected showing coercivity of 0.13 T and magnetization of 90 Am2 kg−1, independently from the electric current density used during annealing. Microstructural investigation reveals the nucleation of the τ‐phase at the grain boundaries of the parent ε‐phase. In addition, the existence of twin boundaries upon nucleation and growth of the metastable phase for all evaluated annealing conditions is observed, resulting in similar extrinsic magnetic properties.

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