Microstructure, ferromagnetic resonance, and electrical analysis of Ho-substituted Li-Ni nanoparticles

The substitution of rare earth ions is a novel approach to vary the dynamic magnetic properties of soft ferrites to such an extent that its electrical properties and ferromagnetic resonance (FMR) response can be set over a broad frequency range. In this work, a complete transmission electron microscopy (TEM), scanning electron microscopy (SEM), ferromagnetic resonance spectroscopy (FMR), X-ray photoelectron spectroscopy (XPS), and current-voltage (I-V) analysis of holmium (Ho) substituted lithium-nickel soft ferrites with composition Li1.2Ni0.4Fe2−xHoxO4 (x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15) is carried out. TEM analysis reveals a spherical shape distribution of nanoparticles with a particle size of ∼ 50 nm. FMR study is carried out to check the role of Ho addition on magnetic energy losses, FMR line position, and shape. The shift in FMR line shape is mainly attributed to the anisotropy contribution, relaxation processes, and ferromagnetic interactions between the magnetic nanoparticles. XPS experiments confirm the presence of all compositional elements along their valence states. The Ho substitution increased the electrical resistivity, whereas the damping of A-B exchange interactions resulted in a decline of Curie temperature (Tc), which is required for high-frequency power applications.