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The magnetic properties of core/shell nanoparticles (NPs) depend on the various parameters, including the magnetic interactions, but these effects have not been well studied. Here, we systematically investigated the structure and magnetic properties of Fe3O4@CoFe2O4 core/shell NPs. X-ray diffraction (XRD), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) confirmed the formation of Fe3O4@CoFe2O4 core/shell NPs. Magnetic measurements of the core/shell NPs were performed on both dried-pressed and well-dispersed in wax states. For the dried-pressed NPs, we found that the temperature-dependent magnetization curves of core/shell NPs vary significantly compared to that of core NPs due to spin interactions at the core/shell interface. Besides, the hysteresis loops of the core/shell NPs at 10 K are constricted, probably due to the interparticle interaction. For the core/shell NPs dispersed in wax, the hysteresis loops were smooth at all temperatures between 10 and 300 K due to the attenuated interparticle interaction. The high HC of 9.14 kOe (at 10 K) of the dispersed NPs is twice larger than that of the dried-pressed powders (4.23 kOe). Our study provides new insights into the effects of shell thickness and interparticle interaction on the magnetic properties of Fe3O4@CoFe2O4 core/shell NPs.

The structural and magnetic properties of Fe/Fe3O4 nanocomposites, synthesized by combined high energy ball milling and controlled oxidation, have been studied. An X-ray diffraction analysis of the crystal structure of the nanocomposites confirmed the coexistence of Fe and Fe3O4 phases. An increase of the oxygen concentration during oxidation process led to the formation of a higher fraction of the Fe3O4 phase with good crystallinity and stoichiometry. The morphology of the nanocomposites revealed a lamella-like structure with a thickness of about 30 nm. The saturation magnetization decreased when the phase fraction of Fe3O4 increased. The coercivity was enhanced at low temperatures (≤100 K) but decreased at high temperatures, due to thermal fluctuation effects on the anisotropy in the Fe3O4 phase. Interestingly, the lamellae exhibited a sharp Verwey transition near 120 K, which is often suppressed or absent in nanostructured Fe3O4 due to the poorly crystalline, off-stoichiometric characteristic. The temperature dependence of high-field magnetization of the lamellae is analyzed by the modified Bloch law. Our study demonstrates the possibility of tuning the magnetism in iron/iron oxide nanosystems through controlled oxidation.

The conversion of metal-modified (Fe, Co) sawdust into magneto-sensitive porous composites using thermal carbonization process in an inert atmosphere was successfully achieved. The as-prepared samples were characterized using nitrogen adsorption, X-ray diffraction, scanning electron microscopy and thermal analysis methods. The obtained results show that the structural and morphological characteristics of the obtained composites depend strongly on the metal precursor’s types. All samples exhibited a good magnetic property and can be easily separated from liquids by an external magnet.

Today, there is an increasing demand for progress in the magnetoimpedance (MI) response of cost-effective soft-magnetic materials for use in high-performance sensing devices. In view of this, we investigate here the field-annealing effects on soft-magnetic properties, magnetoimpedance response, and field sensitivity in the nanocrystalline (Fe3Ni)81Nb7B12 alloy ribbons. We observe that within the low-frequency regime, between 2 and 5 MHz, the zero-field-annealed (ZFA) ribbons exhibit the highest magnetoimpedance values. By magneto-optical Kerr effect measurements, we show that this result stems from the formation of irregular transversally patched magnetic domains after annealing, which in turn explains the induced transverse anisotropy necessary to increase the GMI response. In addition, we discuss this increment in terms of skin effect. Moreover, we report that the highest sensitivity of ca. 189%/(kA/m)—15%/Oe—is achieved for the field-annealed samples whose magnetic field was applied transverse to the ribbon axis. These findings are of practical importance to develop and refine highly sensitive magnetic sensors.

Impact of rapid annealing on the soft magnetic properties of the Fe80Nb3Cu1Si6B10 alloy has been investigated. Parent as-quenched ribbons were prepared by planar flow casting method. Rapid thermal treatments (7-30s) has been conducted at 500°C using the preheated Cu blocks to ensure elevated heating rate of more than 100 K/s. Reference samples were isothermally annealed in the vacuum furnace for 1 h at the same temperature. X-Ray diffraction unveiled formation of nanocrystalline structure of bcc α-Fe(Si) grains, embedded in the residual amorphous matrix in all processed samples, irrespective of the annealing technique. Evolution of coercivity and saturation magnetization values, obtained from the measured hysteresis loops, showed improved magnetic softness of the rapidly annealed samples, compared to the as-quenched and conventionally processed ones. Significant embrittlement of the samples after nanocrystallization has been observed regardless of annealing time and thermal treatment technique used.

Abstract In this study, we demonstrate a one-pot mechanochemical synthesis of the nanocomposite composed of stannite Cu2FeSnS4 and rhodostannite Cu2FeSn3S8 nanocrystals using a planetary ball mill and elemental precursors (Cu, Fe, Sn, S). By this approach, unique nanostructures with interesting properties can be obtained. Methods of XRD, Raman spectroscopy, UV-Vis, nitrogen adsorption, SEM, EDX, HRTEM, STEM, and SQUID magnetometry were applied. Quaternary tetragonal phases of stannite and rhodostannite with crystallite sizes 18–19 nm were obtained. The dominant Raman peaks corresponding to the tetragonal stannite structure corresponding to A-symmetry optical modes were identified in the spectra. The bandgap 1.25 eV calculated from UV-Vis absorption spectrum is very well-acceptable value for the application of the synthesized material. The SEM micrographs illustrate the clusters of particles in micron and submicron range. The formation of agglomerates is also illustrated on the TEM micrographs. Weak ferromagnetic properties of the synthesized nanocrystals were documented.