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In various biomedical applications of iron oxide nanostructures, superparamagnetic nanoneedles offer benefits to access the interior of cells without damage. However, use of superparamagnetic nanoneedles should not be limited to biomedical applications. To explore and extend the field of application, this study is focused on detailed investigation of structural, magnetic, and field emission behavior of iron oxide. Iron oxide nanoneedles are prepared using template-free oleic acid-assisted sol–gel method by varying sols' molarity in the range 0.2–2.0 mM (interval 0.2 mM). Formation of nanoneedles with fine tips and diameter of 20, 23, and 25 nm and length of 700 nm, 1.0 μm, and 1.2 μm at 0.2, 1.0, and 2.0 mM sols are confirmed using Scanning Electron Microscopy. While for rest of the molarity range studied diameter of nanoneedles increases to ~ 50 nm. At 0.2 mM sol magnetite (Fe3O4) phase is observed and vacancy ordered and disordered maghemite (γ-Fe2O3) phases are observed at 0.8–1.0 and 1.4–2.0 mM sols, respectively. Formation of these phases of iron oxide with variation in sols' molarity is also confirmed using FTIR spectra and Raman spectroscopy. Iron oxide nanoneedles show soft magnetic behavior with high saturation magnetization of 73.2, 43.43, and 75.18 emu/g at 0.2, 1.0, and 2.0 mM sols, respectively. These magnetic nanoneedles have potential applications in cell probing. Furthermore, nanoneedles are also tested for their field emission properties. It is observed that nanoneedles, with disordered maghemite phase, synthesized using 2.0 mM sol have high field emission properties along with low turn-on field of 3.77 Vμm−1. Thus, this study reveals ordered and disordered phases of iron oxide using single route. Furthermore, these phases can be utilized for different applications, such as Fe3O4 (at 0.2 mM) phase for biomedical applications and γ-Fe2O3 phase as field emitters. [ABSTRACT FROM AUTHOR]

We have fabricated ZnFe xS (, 0.02, 0.04, 0.06, 0.08 and 0.10) diluted magnetic semiconductors using co-precipitation method. X-ray diffraction patterns depict that ZnFe xS appears as a dominant phase with cubic zinc blende structure and nanoscale crystallite size. In addition, a secondary phase of rhombohedral ZnS also appears; however, no additional phase arises that primarily belongs to Fe dopant. Using Debye-Scherrer relation, the crystallite size is found to be in the range of 20-27nm, which is in good agreement with the crystallite size calculated using the Williamson-Hall (WH) plot method. The appearance of secondary phase provoked to study the residual strain using Stokes-Wilson equation, which is nearly consistent to that observed using WH plot method. The surface morphology, revealed using scanning electron microscopy, depicts non-uniform surface structure with a variety of grains and void dimensions. Hysteresis loops measured for ZnFe xS at room temperature (RT) illustrate a paramagnetic behavior at higher fields; however, small ferromagnetic behavior is evident due to the small openings of the measured hysteresis loops around the origin. The measured RT ferromagnetism reveals the potential spintronic device applications of the studied diluted magnetic semiconductors. [ABSTRACT FROM AUTHOR]