Aggregation vs Surface Segregation: Antagonism over the Magnetic Behavior of NiCr Nanoparticles

Annealing is a valuable method for fine-tuning the ultrasmall magnetic properties of alloy nanoparticles (NPs) by controlling their sizes, modifying their surfaces, and affecting their magnetic interactions. Herein, we study the effect of moderate annealing (450°C) on strongly interacting NiCr nanoparticle assemblies (0 <= atom % Cr ≤ 15) immediately after deposition. Concurrent temperature-dependent electron microscopy and magnetization data demonstrate the interplay of two competing factors, namely, enhanced particle aggregation and element-specific surface segregation, on the magnetic properties, with the former boosting and the latter suppressing them. Strong interparticle interactions can lead to a magnetic response different from that of superparamagnetic particles, namely, from canonical spin-glass (0 atom % Cr) to correlated spin-glass (5-15 atom % Cr) behavior below higher spin-glass transition temperatures T-g (20-350 K). The observation of "high-field susceptibility" below cryogenic temperatures (≤20 K) is ascribed to the presence of inhomogeneity/defects caused by Cr segregation. This work emphasizes the necessity of taking into account the delicate balance of such competing factors to understand the magnetic properties of nanoparticulate samples

Nanostructured ZnFe2O4: An Exotic Energy Material

International audienceMore people, more cities; the energy demand increases in consequence and much of that will rely on next-generation smart materials. Zn-ferrites (ZnFe2O4) are nonconventional ceramic materials on account of their unique properties, such as chemical and thermal stability and the reduced toxicity of Zn over other metals. Furthermore, the remarkable cation inversion behavior in nanostructured ZnFe2O4 extensively cast-off in the high-density magnetic data storage, 5G mobile communication, energy storage devices like Li-ion batteries, supercapacitors, and water splitting for hydrogen production, among others. Here, we review how aforesaid properties can be easily tuned in various ZnFe2O4 nanostructures depending on the choice, amount, and oxidation state of metal ions, the specific features of cation arrangement in the crystal lattice and the processing route used for the fabrication

Design of various Ni–Cr nanostructures and deducing their magnetic anisotropy

Understanding the effects of interparticle interactions is a vital problem because magnetic nanoparticles showcase a variety of magnetic configurations due to different contributions to their total energy. To derive reliable and robust properties from magnetic nanoparticles, it is, thus, necessary to understand the competition between particle anisotropy and interparticle interactions that define the magnetic state of nanoparticles, where size control plays an important role. Here, we apply the random anisotropy model (RAM) that considers various magnetic interactions to selectively prepared NiCr nanostructures (NiCr dense nanoclusters, nanogranular NiCr thin films, and Ag(NiCr) nanocomposites) with different interparticle interactions. The estimated single-particle magnetic anisotropy K values (2.82 − 12.3 × 104 J/m3) and careful analysis of magnetization behavior for these nanostructures reveal that orbital hybridization, surface segregation, and interface character govern the magnetic interactions among nanoparticles. Our study demonstrates how magnetic behaviors vary in these different magnetic systems consisting of superparamagnetic (SPM) and ferromagnetic (FM) contributions specific to magnetic interactions