This study demonstrates the improvement of core loss through the reduction of eddy current loss in soft magnetic composites (SMCs) composed of TiO₂-coated Fe powder and epoxy resin. A thin and uniform TiO₂ insulating layer was successfully deposited on the surface of Fe powder via a sol-gel process, employing titanium (IV) butoxide (TBOT) as the precursor. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses confirmed the formation of a core/shell Fe/TiO₂ structure, with a coating thickness of several tens of nanometers. Increasing the TBOT concentration and coating duration time led to an improved quality factor (Q factor) and a shift of the maximum Q factor values to higher frequency regions. Notably, the permeability was decreased slightly from 14.2 to 13.4, but the core loss, measured at various AC frequencies under 20 mT and then separated into hysteresis loss and eddy current loss at 1 MHz, was significantly reduced from 573 to 435 kW/m³ when the Fe powder was coated with TiO₂ using a 2.5 wt.% TBOT solution for 8 h. This reduction in core loss is attributed to the effective suppression of inter-particle eddy currents by the TiO₂ insulation layer.

We carefully investigated the effects of La-Co co-substitution and magnetic field pressing (MFP) on the structural and magnetic properties of SrM hexaferrites. Samples composed of Sr_1−xLa_xFe_12−xCo_xO₁₉ were sintered at 1230 °C for 2 h in air with sintering additives composed of 0.7 wt% CaCO₃ and 0.7 wt% SiO₂. A single M-type phase was confirmed to exist up to x = 0.3. Rietveld refinement revealed a slight decrease in lattice parameter a and the unit cell volume (V_cell) with an increasing x, while parameter c showed a significant decrease. The saturation magnetization (M_s) values increased from 70.90 to 72.40 emu/g with an increasing x from 0.0 to 0.15 and then decreased to 71.38 emu/g with further increasing of x to 0.3, while the anisotropy field (H_a) increased from 17.7 to 25.9 kOe, leading to a continuous increase in the intrinsic coercivity (H_ci), from 3.52 to 5.00 kOe, respectively. Using the MFP process, the c-axis of M-type hexaferrite grains could be effectively aligned to the applied field direction, which significantly affected the microstructures and, thus, magnetic properties of samples. Unlike non-MFP samples, exhibiting a significant increase in the average grain size (d_avg) but almost unaltered average thickness (t_avg) with an increasing x from 0.0 to 0.3, MFP-processed samples exhibited almost unaltered d_avg values but a continuous decrease in t_avg. Consequently, the variation in remanent flux density (B_r) versus x followed that of M_s versus x and thus exhibited the highest B_r of 4.05 kG for x = 0.15, leading to the highest maximum energy product {(BH)_max} of 3.62 MGOe. With an increasing x from 0.0 to 0.3, the H_ci values continuously increased from 3.14 to 3.84 kOe mainly due to a continuous increase in H_a, although they were significantly lowered in comparison with those of non-MFP samples because of a large increase in B_r for a given composition x. A higher M_r/M_s ratio always resulted in a larger (BH)_max in our samples regardless of x. A careful comparison of the microstructures and magnetic properties between MFP and non-MFP samples provided valuable insights into a broad area of permanent magnet optimization.

Rare-earth permanent magnets, such as Nd₂Fe₁₄B, have been widely used in electric vehicle and wind turbine motors due to their high anisotropy field (H_a), saturation magnetization (M_s) and coercivity (H_c). Cerium (Ce) has gained attention as a potential alternative to neodymium (Nd) due to its high abundance and low cost. The relatively poor intrinsic magnetic properties of Ce magnets, however, remain a significant challenge for their industrial applications. In this study, the synthesis of Ce-based RE₂Fe₁₄B (2-14-1) phases was achieved by a modified reduction-diffusion (R-D) process using REFeO₃ (RE = Ce, Nd) as a precursor. The precursor was prepared by a solid-state reaction with CeO₂, Nd₂O₃, Fe₂O₃ and Fe powders, which is a much more suitable process for mass production and cost-effectiveness. Optimal composition and heat treatment conditions enabled the formation of single-phase Ce-based 2-14-1 particles. The as-synthesized single-phase Ce₂Fe₁₄B particles exhibited an M_s value of ~120 emu/g and an intrinsic coercivity (H_ci) value of ~85 Oe, which can be attributed to the large particle size as observed by FE-SEM.