Correlations between selecting crystallization temperature and modulating α-Fe/amorphous complex phase structure in extending frequency characteristic of the Fe-Si-B-Nb-Cu ultra-thin ribbons

Fe-Si-B-Nb-Cu nanocrystalline ribbons, with thicknesses exceeding 20 μm, have been extensively utilized in designing magnetoelectric devices. Recent advancements in automotive electronics and 5 G technology have shifted the focus to higher working frequencies reached to MHz, making ultra-thin ribbons (below 20 μm) more desirable. However, its fully amorphous structure often complicate the adjustment of the α-Fe/amorphous complex phase structure (α-Fe/amor CPS), subsequently affecting frequency characteristics. The study investigated the controllability of α-Fe crystallization behaviors and focused on the relationship between the initial crystallization temperature ( T_a2) and the initial crystallization volume fraction ( v_i). The findings suggest that selecting ultra-thin ribbons and controlling T _a2 to maintain v_i below 4 % is effective in adjusting α-Fe crystallization behaviors, achieving a uniform α-Fe/amor CPS with substantial v_α-Fe, enhancing the frequency characteristics by technology magnetization process. In a notable example, ribbons with a thickness of 15 ± 1 μm, crystallized at T _a2 = 490 ℃ with a v_i of approximately 0.94 %, achieved a uniform α-Fe/amorphous CPS with nano-sized α-Fe grains (average diameter of D_α-Fe = 13.4 nm) and a high grain number density ( N_{d, α-Fe}) of about 3.0 × 10 ²³ m ⁻³ and a high volume fraction ( v_α-Fe) 37.78 %. This resulted in a magnetized permeability ( μ_i) of 5800 at 1 MHz and an impedance ( Z) peak of approximately 126 Ω at 40 MHz.