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

Competing Magnetic Interactions in Inverted Zn-Ferrite Thin Films

Zn-ferrite is a versatile material among spinels owing to its physicochemical properties, as demonstrated in rich phase diagrams, with several conductive or magnetic behaviors dictated by its cation inversion. The strength and the type of cation inversion can be manipulated through the various thermal treatment conditions. In this study, inverted Zn-ferrite thin films prepared from radio frequency magnetron sputtering were subjected to different in situ (in vacuum) and ex situ (in air) annealing treatments. The temperature and field dependence of magnetization behaviors reveal multiple magnetic interactions compared to its bulk antiferromagnet behavior. Using the magnetic component model, the different magnetic interactions can be explained in terms of superparamagnetic (SPM), paramagnetic (PM), and ferrimagnetic (FM) contributions. At low temperatures, the SPM and FM contributions can be approximated to the hard and soft ferrimagnetic phases of Zn-ferrite, respectively, which changes with the annealing temperature and sputter power. Distinct magnetic properties emanating from in situ annealing compared to the ex situ annealing were ascribed to the nonzero Fe2+/Fe3+ ratio, leading to the different magnetic interactions. The anisotropy was found to be the key parameter that governs the behavior of annealed in situ samples