The effects of magnetic field intensity on the magnetic properties of Fe₈₀Si₉B₁₁ amorphous alloys during magnetic annealing

Highlights

• The magnetic and mechanical properties improved with an increase of the magnetic field intensity.

• Applying a small magnetic field can obviously enhance the magnetic and mechanical properties.

• Spherical symmetry clusters can be observed during the magnetic field annealing process.

Abstract

Magnetic field annealing is an important method to enhance the magnetic properties of amorphous alloys. In this work, the effects of magnetic field annealing intensity on the magnetic properties, mechanical properties, and microstructure of Fe₈₀Si₉B₁₁ amorphous ribbons were investigated. It can be seen from the results that the magnetic induction at 1600 A/m (B₁₆₀₀), maximum permeability (μ_m), coercivity (H_c), Elastic modulus (E_r), and Hardness were improved with an increase of the magnetic field intensity. When the magnetic annealing intensity was 2.5 × 10⁻⁴ T, the B₁₆₀₀, μ_m, H_c, E_r and Hardness of the sample were improved by 9%, 298%, 67%, 23% and 3%, respectively, compared with those of the as-spun sample. TEM results showed that there are some spherical symmetric clusters present in the 653 K × 2.5 × 10⁻⁴ T sample. This may be an important reason for the improvement of the magnetic properties. Compared with the 653 K × 1 T sample, the magnetic field intensity of the 653 K × 2.5 × 10⁻⁴ T sample was only 0.025%. However, the values of B₁₆₀₀, μ_m, H_c, E_r and Hardness of the latter reached 96%, 82%, 115%, 90% and 94% of the former, respectively. It means that during the magnetic field annealing process, applying only a small magnetic field can obviously enhance the magnetic and mechanical properties of Fe₈₀Si₉B₁₁ amorphous alloy. This provides a theoretical basis for the further improvement of the magnetic and mechanical properties of Fe₈₀Si₉B₁₁ alloys, and in the energy saving. The reasons for the changes of magnetic and mechanical properties caused by different magnetic field intensities are discussed.

Introduction

Soft magnetic amorphous alloys are widely used in the fields of power electronic devices such as transformers, memories, magnetic shields, and sensors [[1], [2], [3], [4], [5]], which have had a huge impact on human life. In the new era of rapid development, it is a necessary trend that the soft magnetic amorphous materials become lighter, stronger and more energy-saving [6]. This requires soft magnetic amorphous alloys to possess better magnetic properties such as high permeability，high saturation magnetisation, and low coercivity, etc. [[7], [8], [9]]. Fe–Si–B amorphous alloys have unique advantages in terms of high permeability，high saturation magnetisation, and low loss, and they are widely used in high-efficiency, energy-saving, miniaturisation and integration equipment [[10], [11], [12], [13], [14], [15]].

Magnetic field annealing is a typical method to improve the soft magnetic performance of magnetic materials before industrial applications [[16], [17], [18], [19], [20], [21], [22]]. This method was applied in amorphous alloys as early as the 1970s [23,24]. However, magnetic field annealing usually leads to the destruction of the mechanical properties [25,26] which will cause magnetic leakage and short circuits. The effect of magnetic field annealing on amorphous alloys has been extensively studied. García-Prieto et al. [24] found that magnetic annealing induces macroscopic magnetic anisotropy and thus enhances the magnetic properties of amorphous alloys. Degro et al. [27] found that magnetic field annealing results in structural relaxation in the amorphous alloy which reduces the number of mobile defects and thus, improves the magnetic properties. Roman et al. [28] found that magnetic field annealing can form a certain number of movable atom pairs, and the magnetic domain structure becomes non-uniform. Li et al. [29] found that magnetic field annealing can improve the magnetic properties of amorphous alloys. This is attributed to the formation of nanocrystals and structural relaxation (release of internal stress and defects). In our recent research [30], we have studied the heat treatment of Fe₈₀Si₉B₁₁ amorphous ribbons under 1 T magnetic field. It was found that the magnetic properties gradually improved with the increase of annealing temperature. When the annealing temperature was 653 K (close to the Curie temperature (T_C)), the best magnetic properties of the alloy were obtained. The magnetic properties decreased when the annealing temperature was higher than T_C. The reason may be that the alloy transforms from ferromagnetic to paramagnetic above T_C.

During the magnetic annealing process, magnetic field intensity has a very important effect on the magnetic properties of the alloys [[27], [28], [29], [30], [31]]. Roman et al. [28] found that increasing the magnetic field intensity is beneficial to the soft magnetic properties of the amorphous alloys. When the magnetic field intensity increased from 8 kA/m to 160 kA/m, the B_r and H_c of the Co_71.5Fe_2.5Mn₂Mo₁Si₉B₁₄ amorphous alloy decreased from 0.42 T to 4.8 A/m to 0.01 T and 1.6 A/m, respectively. However, Fan et al. [31] found that increasing the magnetic field intensity damages the magnetic properties of amorphous alloys. The magnetic permeability of the Co₇₁Fe₂Si_14-xB_9+xMn₄ amorphous alloy gradually decreased with increasing the magnetic field intensity. Obviously, there is no unified understanding of the influence of magnetic field intensity on magnetic properties during the magnetic annealing process. In this paper, based on our previous research [30], we set a fixed annealing temperature (653 K), and the effects of the magnetic field intensity during the annealing process on the magnetic and mechanical properties were investigated for Fe₈₀Si₉B₁₁ amorphous ribbons.