Y.I. Lee

Inhomogeneity on texture, microstructure and magnetic properties of hot deformed R2Fe14B-typed magnet

The inhomogeneity on texture, microstructure and magnetic properties of hot deformed (HD) disc shape R2Fe14B-typed magnets along radial and axial directions has been investigated. HD disc shape NdFeB magnet exhibits inhomogeneous texture, grain morphologies and magnetic properties not only along the radial direction but also along the axial direction. Higher magnetic properties can be found in the middle part of the HD magnet, due to the existence of larger volume fraction of plate-like Nd2Fe14B grains and the well c-axis alignment parallel to the pressing direction. In addition, particle-like and coarser grains are easily found not only in the bottom but also in the edge of the HD magnet, which may degrade the magnetic performance of the samples cut from those parts. Owing to the inhomogeneity of (00L) texture and grain morphologies along axial and radial directions, the optimal magnetic properties of Br = 12.7 kG, Hci = 5.1 kOe and (BH)max = 39 MGOe can be obtained only in the middle sample of HD magnet...

Magnetic properties improvement of melt spun Co 86.5 Hf 11.5 B 2 nanocomposites by refractory elements substitution

Last decades, rare-earth (RE) containing nanocomposites with improved remanence, B_r, and maximum energy product, (BH)_max, have been investigated extensively for bonded magnet applications. However, the demand for rare-earth permanent magnets is rapidly increased, leading to the shortage and price rising of rare earth elements. Therefore, it is significant to explore the RE-free permanent magnetic materials which are possible for industrial applications. Recently, RE-free Co-Hf-B system has been reported to exhibit attractive permanent magnetic properties. Especially, Br=0.75T, _iH_c = 248 kA/m, and (BH)_max = 61.6 kJ/m³ have been achieved in Co₈₅Hf₁₂B₃ recently. However, limited study related to the elemental substitution effect on the magnetic and structural characterizations of Co-Hf-B alloys is available. In the paper, Co-rich Co_86.5Hf_11.5B₂ is selected as an initial composition, and the effect of refractory elements substitution, including Ti, Cr, Nb, Zr, on the structural and magnetic properties of Co_86.5Hf_10.5MB₂ alloys are investigated. The melt spinning method is adopted to prepare the isotropic nanocomposite samples at a high wheel speed of 40 m/s in this work.

Effect of the external field on the soft magnetic properties and microstructure of directly cast Fe75P8.7B5C7Si4.3 nanocrystalline sheets

A new method to fabricate soft magnetic bulk metallic glasses (BMGs) by an injection casting with applying external magnetic field during solidification has been developed. The effect of applying magnetic fields (Ha) on soft magnetic properties and microstructure of Fe75P8.7B5C7Si4.3 alloy sheets with dimension of t × 4 mm × 15 mm (t = 1–3 mm) have been studied. The microstructure shows that the fully amorphous is attained by the applying magnetic field even at the core region of the thicker sheets with t = 3 mm. All studied sheets exhibit similar saturation magnetization of 1.23–1.25 T, but the coercivity and resistivity are strongly dependent on the thickness t and the strength of magnetic field Ha, where Hc increases with t, the slope of Hc versus t decreases with the increase of Ha, and the resistivity increases with the increase of Ha. The changes of coercivity and resistivity are strongly related to the fully amorphous induced by Ha. The external magnetic field has significant improvement in glass f...

Magnetic behaviors in melt spun Fe52−xMn23+xGa25 (x = 0–3) ribbons

The effect of volume fraction of B2-type ferromagnetic (FM) phase on magnetic behavior of melt-spun Fe52−xMn23+xGa25 (x = 0, 1, 2, and 3) ribbons has been investigated. X-ray diffraction (XRD) results show that the volume fraction of the B2 phase is decreased, accompanied by the increased antiferromagnetic (AFM) fcc phase, with increasing x. The magnetization isotherms of these ribbons at different temperatures demonstrate that there exists a critical field HCR from AFM to FM state, and the HCR decreases and vanishes finally with increasing temperature. High exchange bias field (HEB) at 10 K through a cooling field at HCR from 300 K could be found and correlated to the volume fraction of B2-type FM phase. Both HCR and HEB are increased with decreasing the amount of B2-type FM phase. The HCR is increased from 20 kOe for x = 0 to 50 kOe for x = 3, and HEB is increased from 0.9 kOe for x = 0 to 2.5 kOe for x = 2. The latter phenomenon might be attributed to the change of exchange interactions at FM/AFM inter...