We report on the realization of particle size, morphology, and chemical composition controlled cobalt ferrite nanoparticles (CFO NPs) with tunable magnetic properties for application in electronic and electromagnetic devices. The effect of oleic acid concentration (0.0–0.1 M) on the structural, physical, chemical, electronic, and magnetic properties of solvothermally synthesized CFO NPs is investigated in detail by using the oleic acid (OA) based chemical method for synthesis. Crystalline, cubic, and chemically homogeneous CFO NPs (5–15 nm) can be obtained by controlling the OA concentration. Spectroscopic analyses revealed that the OA molecules form covalent bonds with CFO NPs. The particle-size control was achieved by bridging bidentate interactions between the OA molecules and CFO NPs. Detailed magnetic measurements revealed that the OA concentration helps to effectively control the magnetic behavior of particle-size-controlled CFO NPs. The interfacing between OA molecules and CFO surface atoms leads to modified magnetism which is the key to understand the underlying mechanisms and utilize magnetic nanoparticles in practical applications. The anisotropy constant variation directly with nanoparticle size indicates that the magnetocrystalline component governs the magnetic anisotropy in OA coated CFO. Removal of OA (after thermal treatment) induces enhanced magnetic anisotropy and exchange bias as consequence of surface component. The results and analyses suggest that the molecular coating of nanoparticles offers the most important and critical step to design novel nanostructured magnetic materials for current and emerging electronic device technologies.

Cobalt (Co) nanoparticles (NPs) were produced by a simple, one step hydrothermal method with the capping of oleic acid. Intrinsic structural, physiochemical and magnetic properties of Co NPs were investigated and demonstrated their applicability in biomedicine. X-ray diffraction, Raman spectroscopy and infrared (IR) spectroscopic studies confirm the single phase Co NPs with a high structural quality. The IR data revealed the capping of oleic acid via monodentate interaction. Small angle scattering studies suggest the existence of sticky hard sphere type of interaction among the Co NPs because of magnetic interaction which is further evidenced by electron microscopy imaging analyses. The Co NPs exhibit a ferromagnetic character over a wide range of temperature (20-300 K). The temperature dependence of magnetic parameters namely, saturation magnetization, remanent magnetization, coercivity and reduced remanent magnetization were determined and correlated with structure of Co NPs. The Cytotoxicity studies demonstrate that these Co NPs exhibit the mild anti-proliferative character against the cancer cells (cisplatin resistant ovarian cancer (A2780/CP70)) and safe nature towards the normal cells. Haemolytic behaviour of human red blood cells (RBC) revealed (<5%) haemolysis signifying the compatibility of Co NPs with human RBC which is an essential feature in vivo biomedical applications without creating any harmful effects in the human blood stream.

The authors report on the effect of manganese (Mn) substitution on the crystal chemistry, morphology, particle size distribution characteristics, chemical bonding, structure, and magnetic properties of cobalt ferrite (CoFe 2 O 4 ) nanoparticles (NPs) synthesized by a simple, cost-effective, and eco-friendly one-pot aqueous hydrothermal method. Crystal structure analyses indicate that the Mn(II)-substituted cobalt ferrites, Co 1– x Mn x Fe 2 O 4 (CMFO, x = 0.0–0.5), were crystalline with a cubic inverse spinel structure (space group Fd 3 m ). The average crystallite size increases from 8 to 14 nm with increasing Mn(II) content; the crystal growth follows an exponential growth function while the lattice parameters follow Vegard’s law. Chemical bonding analyses made using Raman spectroscopic studies further confirm the cubic inverse spinel phase. The relative changes in specific vibrational modes related to octahedral sites as a function of Mn content suggest a gradual change of measure of inversion of the ferrite lattice at nanoscale dimensions. Small-angle X-ray scattering and electron microscopy revealed a narrow particle size distribution with the spherical shape morphology of the CMFO NPs. The zero-field-cooled and field-cooled magnetic measurements revealed the superparamagnetic behavior of CMFO NPs at room temperature. The sample with x = 0.3 indicates a lower value of blocking temperature (9.16 K) with the improved (maximum) value of saturation magnetization. The results and the structure-composition–property correlation suggest that the economic, eco-friendly hydrothermal approach can be adopted to process superparamagnetic nanostructured magnetic materials at a relatively lower temperature for practical electronic and electromagnetic device applications.

Engineering cobalt ferrites for application in health and biomedical science poses a challenge in terms of nanoscale morphology with a controlled size, shape, and thermochemical stability coupled with controlled properties for biocompatibility. Here, we report a simple one-step, low temperature approach to produce crystalline, nanosized cobalt ferrites (CFO) with a size ∼4.7 nm and demonstrate their applicability in breast cancer treatment. Inherent physiochemical and magnetic properties, which are quite important for biomedical applications, along with cytotoxicity of CFO nanoparticles (NPs) are investigated in detail. X-ray diffraction analyses confirm the cubic spinel phase with the tensile strain in crystalline CFO NPs. Chemical bonding analyses using infrared and Raman spectroscopic studies also support the cubic spinel phase. Electron microscopy and small-angle X-ray scattering revealed the narrow particle-size distribution and spherical-shape morphology. The as-synthesized CFO NPs exhibit superparamagnetic character. Unsaturated magnetization behavior suggests the existence of disordered spins in the surface layers. The temperature dependence of the magnetic parameters, namely, saturation magnetization, coercivity, retentivity, and squareness ratio, also supports the surface-localized spins. Cytotoxic activity of the as-synthesized CFO NPs against the human breast cancer (MCF-7) cell line and normal human peripheral blood mononuclear cells (PBMC) has been evaluated. The mild response of CFO NPs in terms of their antiproliferative nature against cancer cells and negligible Cytotoxicity reflecting their human-safe-and-friendly nature makes them suitable for bioapplications. Moreover, assessment of toxicity toward human red blood cells (RBC) revealed (<3%) hemolysis as compared to the positive control, suggesting potential applications of CFO NPs for human cells.

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Recently, phase change chalcogenides, such as monochalcogenides, are reported as switching materials for conduction‐bridge‐based memristors. However, the switching mechanism focused on the formation and rupture of an Ag filament during the SET and RESET, neglecting the contributions of the phase change phenomenon and the distribution and re‐distribution of germanium vacancies defects. The different thicknesses of germanium telluride (GeTe)‐based Ag/GeTe/Pt devices are investigated and the effectiveness of phase loops and defect loops future application in neuromorphic computing are explored. GeTe‐based devices with thicknesses of 70, 100, and 200 nm, are fabricated and their electrical characteristics are investigated. Highly reproducible phase change and defect‐based characteristics for a 100 nm‐thick GeTe device are obtained. However, 70 and 200 nm‐thick devices are unfavorable for the reliable memory characteristics. Upon further analysis of the Ag/GeTe/Pt device with 100 nm of GeTe, it is discovered that a state‐of‐the‐art dependency of phase loops and defect loops exists on the starting and stopping voltage sweeps applied on the top Ag electrode. These findings allow for a deeper understanding of the switching mechanism of monochalcogenide‐based conduction‐bridge memristors.