Influence of Annealing Process on Soft Magnetic Properties of Fe-B-C-Si-P Amorphous Alloys

Abstract

It is well known that the annealing process plays a key role in tuning the properties of Fe-based amorphous soft magnetic alloys. However, the optimal annealing process for a particular amorphous alloy is often difficult to determine. Here, Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloys (denoted as Fe_81.4 and Fe_82.2) were prepared to systematically study the effects of the annealing temperature and time on the soft magnetic properties. The results show that the optimum annealing temperature ranges of the Fe_81.4 and Fe_82.2 amorphous alloys were 623 K to 653 K and 593 K to 623 K, and their coercivity (H_c) values were only 2.0–2.5 A/m and 1.3–2.7 A/m, respectively. Furthermore, a characteristic temperature T_ai was obtained to guide the choosing of the annealing temperature at which the dB_s/dT begins to decrease rapidly. Based on the theory of spontaneous magnetization, the relationship between T_ai and the optimum annealing temperature ranges was analyzed. When the annealing temperature was higher than T_ai, the effect of the internal magnetic field generated by spontaneous magnetization on the relaxation behavior was significantly reduced, and the alloys exhibited excellent soft magnetic properties. It is worth indicating that when annealed at 603 K (slightly higher than T_ai), the Fe_82.2 amorphous alloys exhibited excellent and stable soft magnetic properties even if annealed for a long time. The H_c of Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloys was only 1.9 A/m when annealed at 603 K for 330 min. This value of T_ai is expected to provide a suggestion for the proper annealing temperature of other amorphous soft magnetic alloys.

1. Introduction

Among the diverse soft magnetic materials, Fe-based amorphous alloys have attracted intensive attention due to their highly comprehensive soft magnetic performance, including low coercivity (H_c) and core loss (W) [1,2,3,4]. The structure of Fe-based amorphous alloys obtained through rapid solidification has various inhomogeneities, such as loose and dense atomic packing regions, regions with different internal stresses, and magnetic heterogeneous regions [5]. The H_c of Fe-based amorphous alloys is directly related to the inhomogeneity, internal stress, and free volume of amorphous alloys [5,6,7,8]. In order to reduce H_c and improve the soft magnetic properties, annealing is generally carried out near or above the Curie temperature (T_C) of amorphous alloys [5,9]. Above T_C, amorphous alloys are paramagnetic, so the stress release and structural relaxation are no longer affected by the local internal magnetic field [5,9,10]. Therefore, the magnetic domain structure is optimized, thus greatly improving the soft magnetic properties.

At present, the annealing time of amorphous alloys reported in the literature is relatively short, especially for those with a relatively high iron content; most of them are no more than 30 min [9,11,12,13,14,15]. However, for the industrial production of amorphous alloy products, long-time annealing is of great importance. Due to the characteristics of the furnace structure and the large volume of materials, the time required for uniform temperature distribution in the industrial production process is longer than that under experimental conditions. The time required to reach the set temperature for different locations in the furnace is different, but the properties of materials annealed in the same batch need to be as similar as possible. Therefore, it is required that the properties of amorphous alloys be kept stable during the annealing time for as long as possible.

A few studies have suggested that when annealing for a long time, even if the annealing temperature is slightly lower than T_C, good soft magnetic properties can also be obtained [16,17]. Thus, the question of how to determine the optimal annealing temperature for long-time annealing is important. T_C is a key temperature parameter used to describe the property transition of magnetic materials from ferromagnetic to paramagnetic; it is often used as a criterion for selecting the optimal annealing temperature in short-time annealing. Similarly, it is important to find a way to determine the optimal annealing temperature in long-time annealing and to understand the variation in magnetic properties with temperature.

In this study, Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloys with relatively high Fe content were designed and prepared. The effects of the annealing temperature and time on the soft magnetic properties, magnetic domain structure, and magnetization process of the amorphous alloys were systematically studied. The correlation between the magnetic properties and the structure of the annealed amorphous alloys is discussed, and the process for the magnetic property adjustment of Fe-based amorphous alloys in long-time annealing is investigated.

2. Materials and Methods

Amorphous alloy ribbons with nominal compositions of Fe_81.4B_13.2C_2.8Si_1.8P_0.8 (denoted as Fe_81.4) and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 (denoted as Fe_82.2) were produced with single-roller spinning. The thermal properties of the amorphous alloys were examined using differential scanning calorimetry (DSC, Netzsch STA 449 F3, Netzsch, Selb, Germany) at a heating rate of 40 K/min. The temperature dependence of magnetization of the amorphous alloys was measured using superconducting quantum interference device (SQUID, MPMS-3, Quantum Design, San Diego, CA, USA) magnetometry under an applied field of 800 kA/m at a heating rate of 10 K/min. The ribbons, with a width of about 1 mm and a thickness of about 25 μm, were cut to an 80 mm length for subsequent annealing and measurements. The structures of the as-spun and annealed samples were identified using X-ray diffraction (XRD, Rigaku D/max 2500, Rigaku, Tokyo, Japan) with Cu Kα radiation. The structure of the as-spun Fe_82.2 amorphous alloy ribbon was also identified using high-resolution transmission electron microscopy (HRTEM, FEI Tecnai G2 F20, FEI, Hillsboro, OR, USA). The static magnetization curves and hysteresis loops were measured using a DC B-H hysteresis loop tracer (Linkjoin MATS-2010SD, Linkjoin, Loudi, China) under a field of 800 A/m. The domain structures were observed with a magneto-optical Kerr microscope (MOKE, Zeiss Imager D2m, Zeiss, Oberkochen, Germany).

In order to explore the effect of the annealing process on the soft magnetic properties of amorphous alloys, isothermal annealing treatments of the amorphous ribbons were carried out with the normal annealing (NA) process. This consisted of the following three steps: (1) the ribbon sample was fixed in a copper holder and then sealed in a quartz tube filled with argon gas; (2) the temperature inside the electric tube furnace was raised to the set value, and the quartz tube was pushed into the furnace; (3) after holding in the furnace for a given time, the quartz tube was pulled out of the furnace and quenched in water to room temperature.

3. Results and Discussion

In order to enhance the saturation magnetic flux density (B_s) of Fe-based amorphous alloys, the Fe content should be increased in the alloys. Based on former research results and considering the synergetic effect of metalloid elements B, C, Si, and P [17,18,19,20,21], two alloys with nominal compositions of Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 were designed and prepared via single-roller spinning. The structure of the prepared alloy ribbons was examined using the XRD method. As shown in Figure 1, no sharp diffraction peak corresponding to the crystalline phases in the XRD patterns of the as-spun Fe_81.4 and Fe_82.2 ribbons (black lines in Figure 1a and Figure 1b, respectively) can be observed, indicating that both of them possessed an amorphous structure. The HRTEM image and SAED pattern in Figure 2 further confirm the amorphous nature of the as-spun Fe_82.2 ribbon. This implies that the designed alloys possessed good glass-forming abilities. The thermal properties of the as-spun ribbons, including the Curie temperature (T_C) and the onset temperature of crystallization (T_x), were determined from the DSC curves shown in Figure 3. The T_C and T_x of the Fe_81.4 amorphous ribbons were 661 K and 776 K, respectively, and those of Fe_82.2 were 635 K and 766 K, respectively. This indicates that the value of T_x−T_C was over 110 K. When the Fe content was slightly increased by 0.8 at.% (the B content was reduced by 0.8 at.%), the T_C and T_x of the Fe-based amorphous alloy were clearly reduced. The decrease in the T_x is due to the decrease in thermal stability caused by the increase in Fe content and the decrease in B content [22,23]. Meanwhile, the decrease in T_C is due to the decrease in the exchange interaction [18,24].

The amorphous ribbons were annealed at different temperatures from 563 K to 663 K with an interval of 10 K. Figure 4 shows the annealing temperature dependence of coercivity (H_c) and the magnetic flux density measured at an applied magnetic field of 800 A/m (B₈₀₀) for the Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloy ribbons after normal annealing for 90 min. With the increase in the annealing temperature, the H_c decreased to a low point at first, then maintained a stable state and finally increased rapidly. The stable region with the lowest H_c obtained in the experiment is defined as the optimal annealing temperature range. The lowest temperature of the optimum annealing temperature range is denoted as T_a0, and the highest temperature is denoted as T_am. The T_a0 and T_am of the Fe_81.4 amorphous alloy were 623 K and 653 K, respectively, while the T_a0 and T_am of the Fe_82.2 amorphous alloy were 593 K and 623 K, respectively. As the annealing temperature increased, the B₈₀₀ of the alloys initially increased then reached a plateau and finally declined. B₈₀₀ is a comprehensive reflection of the B_s, H_c, and permeability [25]. The initial temperatures of the B₈₀₀ plateau were 613 K and 573 K for Fe_81.4 and Fe_82.2, respectively, which are lower than T_a0. However, the end temperature of the B₈₀₀ plateau was equal to T_am. The reduction in H_c was due to the relaxation of stress and the reduction in the free volume [6]. However, spontaneous magnetization can affect the relaxation progress of amorphous alloys [5]. Therefore, the beginning of the optimum annealing temperature range of H_c did not coincide with the starting temperature of relaxation. The present results show that both the Fe_81.4 and Fe_82.2 amorphous alloys exhibited an optimized annealing temperature range of 30 K, together with B₈₀₀ and H_c values of 1.64–1.65 T and 2.0–2.5 A/m and 1.65–1.66 T and 1.3–2.7 A/m, respectively. This indicates that, after annealing, the developed amorphous alloys were excellent soft magnetic materials, exhibiting a high B₈₀₀ and low H_c (Figure 4).

In order to understand the effect of elements on the magnetic property, the temperature dependence of the saturation flux density (B_s) for the Fe_81.4 and Fe_82.2 amorphous alloys was obtained and studied (Figure 5). At a temperature of 5 K, the B_s values of the Fe_81.4 and Fe_82.2 amorphous alloys were 1.84 T and 1.92 T, respectively. At a temperature of 5 K, the B_s values of the Fe_81.4 and Fe_82.2 amorphous alloys were 1.84 T and 1.92 T, respectively. When the Fe content increased, the proportion of ferromagnetic atoms increased; thus, the total magnetic moment increased, leading to an increase in the B_s near 0 K [18,26]. As the temperature increased, the atomic thermal motion increased. In ferromagnetic materials, the thermal motion of atoms disturbs the spontaneous magnetization of atomic magnetic moments [24]. As a result, the B_s of the Fe_81.4 and Fe_82.2 amorphous alloys decreased continuously with the increase in temperature, until it reached the lowest point. The temperature with the lowest B_s is denoted as T_x0. When the temperature exceeded T_x0, the B_s began to increase, which was caused by crystallization of the amorphous alloys. Finally, the B_s decreased again because the spontaneous magnetization of α-Fe decreased rapidly. In a sense, T_x0 is the temperature at which crystallization is observed on the B_s(T)–T curve to have a noticeable effect on the magnetic properties.

The shape of the B_s(T)–T curve is related to the strength of the exchange interaction [18,24]. In order to visualize the declining rate of the B_s with increasing temperature, the reduced saturation flux density B_s(T)/B_s(5K) as a function of temperature (T) and the derived first derivative of B_s with respect to T are shown in Figure 6. For the Fe_81.4 and Fe_82.2 amorphous alloys, the B_s(T)/B_s(5K)–T and dB_s/dT–T curves are similar. At first, the B_s(T)/B_s(5K) and dB_s/dT decreased slowly with the increase in temperature. When the temperature continued rising to near the temperature denoted as T_ai, at which B_s(T)/B_s(5K) = 45%, the value of dB_s/dT began to decrease rapidly. Increasing the temperature further, dB_s/dT decreased further and reached the lowest level. The corresponding temperature is denoted as T_C0 (as shown in Figure 6). When the temperature was higher than T_C0 but lower than T_x0, dB_s/dT gradually increased with the increase in temperature. Meanwhile, the decrease in B_s(T)/B_s(5K) developed slowly. In other words, T_C0 represents the temperature at which the spontaneous magnetization of the alloy changed the most dramatically, i.e., the Curie temperature (the temperature at which ferromagnetism transforms into paramagnetism). The value of T_C0 was indeed close to the Curie temperature obtained from the DSC curve (T_C), as shown in

Table 1. Several temperature parameters mentioned in this article for Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloys.

Alloy	Ta0 (K)	Tam (K)	Tai (K)	TC0 (K)	Tx0 (K)	TC (K)	Tx (K)
Fe81.4B13.2C2.8Si1.8P0.8	623	653	620	667	744	661	776
Fe82.2B12.4C2.8Si1.8P0.8	593	623	589	637	709	635	766

T_a0 and T_am are the lowest temperature and the highest temperature of the optimum annealing temperature range, as shown in Figure 4; T_x0, T_ai, and T_C0 are the characteristic temperatures, as shown in Figure 5 and Figure 6; T_C and T_x are the Curie temperature and the onset temperature of crystallization, determined from the DSC curves shown in Figure 3.

.

Although the B_s(T)–T, B_s(T)/B_s(5K)–T, and dB_s/dT–T curves of the Fe_81.4 and Fe_82.2 amorphous alloys are similar, the T_ai and T_C0 of the Fe_82.2 amorphous alloy were lower than those of the Fe_81.4 amorphous alloy. This is due to the difference in the strength of the exchange interaction for the Fe_81.4 and Fe_82.2 amorphous alloys. The metalloid content of the Fe_82.2 amorphous alloy was lower than that of the Fe_81.4 amorphous alloy. The decrease in the metalloid content causes a reduction of the interatomic distance between the Fe atoms [18,24]. According to the Bethe–Slater curve [24], the strength of the exchange interaction will decrease with the decrease in the interatomic distances between Fe atoms. Therefore, the dB_s/dT increases, resulting in a decrease in T_ai and T_C0.

By examining and analyzing the results shown in Figure 4, Figure 5 and Figure 6 , it is not difficult to find that T_a0 is approximate to T_ai. This may have been caused by the effect of spontaneous magnetization on the alloy relaxation process of these amorphous alloys. When the annealing temperature is lower than T_ai but sufficient to allow short-distance movement of the atoms, the thermal motion of the atoms may cause changes in the local structure. On the one hand, long-term heat treatment at this temperature is enough to eliminate the influence of stress on H_c, so that H_c can be reduced compared to the cast state. On the other hand, the spontaneous magnetization is still high. Spontaneous magnetization will strengthen the local magnetic anisotropy [5,9,27], so it is difficult to achieve the optimal low coercivity after annealing. When the annealing temperature is higher than T_ai, the decline in the dB_s/dT value begins to accelerate, and the B_s(T) decreases to less than half of the B_s near 0 K (B_s(T)/B_s(5K) ≤ 45%), which demonstrates that the ferromagnetism of amorphous alloys is greatly weakened. The effect of the inner magnetic field generated by spontaneous magnetization on the relaxation behavior becomes negligible. The magnetic anisotropy of the alloy is reduced, and the soft magnetic properties are greatly improved. Based on the above analysis, we provide a simple way to determine the lowest temperature T_ai (B_s(T_ai)/B_s(5K) = 45%) of the optimum annealing temperature range for the Fe-based amorphous alloys with a relatively low Curie temperature, similar to the current amorphous alloys.

The magnetic domain structures of the amorphous alloy samples that experienced different annealing processes were characterized using a magneto-optical Kerr microscope, and the effect of spontaneous magnetization on the soft magnetic properties is discussed. Figure 7 shows the domain structures of the as-spun, NA-633 K-annealed and NA-603 K-annealed Fe_81.4B_13.2C_2.8Si_1.8P_0.8 amorphous alloy samples in the demagnetized state. There were two types of typical domains in the as-spun Fe_81.4 amorphous alloy sample (Figure 7a): wide-curved domains and narrow fingerprint domains. These are caused by tensile stress and compressive stress [5,28,29]. After normal annealing at 633 K, the domains of the sample appeared as a broad strip pattern oriented slightly away from the length direction of the amorphous ribbon, demonstrating a low domain energy, homogenous structure, and low stress state [30]. In contrast, more domain branches and rugged edges were present in the magnetic domain structure of the NA-603 K Fe_81.4 amorphous alloy sample, and their direction deviated from the length direction, indicating a strong pinning effect. This phenomenon can be attributed to the magnetic anisotropy induced by spontaneous magnetization during the annealing process, because the annealing temperature was lower than T_ai [5,9,27]. This shows that the annealing temperature above T_ai is important for removing the pinning effect to obtain a low H_c, as shown in Figure 4.

T_am is the temperature related to the crystallization of amorphous alloys; above this, after annealing for a certain time, a volume fraction of α-Fe nanocrystalline would precipitate from the amorphous matrix of the alloys. Examples are shown in Figure 1: a few weak but sharp diffraction peaks corresponding to the α-Fe crystalline phase can be detected in the smooth-side XRD patterns of the Fe_81.4 ribbons annealed at 663 K and the Fe_82.2 ribbons annealed at 633 K for 90 min. The HRTEM image in Figure 2 shows that the as-spun Fe_82.2 ribbon is completely amorphous with no pre-existing tiny α-Fe grains before annealing. Thus, the crystallization of Fe_82.2 ribbons annealed at 633 K for 90 min is entirely due to annealing. It has been confirmed that partial crystallization at the surface increases the anisotropy, resulting in an increase in the H_c and deterioration of the soft magnetic properties [31,32,33]. Additionally, the Curie temperature of the α-Fe cluster is higher than that of amorphous alloys, and it further increases with the cluster size and magnetic interaction [9,31], which aggravates the effect of spontaneous magnetization on the relaxation process.

It is well known that amorphous alloys are of a thermodynamic metastable state. They will eventually crystallize as long as the annealing time is long enough at a high enough temperature. Moreover, the higher the annealing temperature is, the shorter the time required for crystallization. Therefore, the T_am is actually also related to the annealing time. When the annealing time is 90 min, crystallization of the Fe_82.2 amorphous alloy occurs at 633 K, resulting in the H_c increasing to 6.3 A/m. However, after annealing at 633 K for 60 min, the H_c of the amorphous alloy is 1.4 A/m; that is, the highest temperature of the optimum annealing temperature range for 60 min is not lower than 633 K.

Figure 8 illustrates the annealing time dependence of H_c and B₈₀₀ for the Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloy ribbons with normal annealing at different temperatures. Three different annealing temperatures were selected for the Fe_82.2 amorphous alloy: T_a1 = 603 K, T_a2 = T_am (90 min) = 623 K, and T_a3 = 633 K, respectively. Overall, with the increase in the annealing time, the B₈₀₀ of the alloys increased initially and then remained relatively stable. When T_a3 = 633 K, the H_c first decreased rapidly as the annealing time increased, then remained stable for a short time (30–60 min), and rose quickly after the annealing time reached 90 min. When T_a2 = 623 K, the H_c showed a concave shape with respect to annealing time: the H_c first decreased rapidly, then decreased to 1.3 A/m after 30 min, and remained below 3 A/m within 30–120 min. Up to an annealing time of 150 min, the H_c rose to 4.6 A/m. However, when the annealing temperature decreased to T_a1 (603 K), the coercivity H_c of the annealed samples exhibited very strong stability with the increase in annealing time. Even when the annealing time was extended to 330 min, the H_c was still only 1.9 A/m. For the Fe_82.2 amorphous alloy, T_a1 was slightly higher than T_ai (T_a1 − T_ai < 15 K).

The annealing time dependence of H_c and B₈₀₀ for the Fe_81.4B_13.2C_2.8Si_1.8P_0.8 amorphous alloy ribbons with normal annealing at different temperatures is shown in Figure 9. Two different annealing temperatures were selected for the Fe_81.4 amorphous alloy, which were T_a4 = 633 K and T_a5 = 663 K, respectively. For both annealing temperatures, with the increase in annealing time, the B₈₀₀ increased rapidly at first and then became stable. When the annealing temperature was T_a4 = 633 K, the H_c rapidly decreased to about 1 A/m and then slowly increased. The H_c remained at 2.7 A/m after 150 min of annealing. However, when the annealing temperature increased to T_a5 = 663 K, the H_c remained relatively stable only within 30–60 min, and at this time, the H_c was 2.8–3.7 A/m, which was significantly higher than that at 633 K. Although the H_c of the Fe_81.4 amorphous alloy shown in Figure 9 is higher than that of the Fe_82.2 amorphous alloy shown in Figure 8, it can also be seen that when the annealing temperature is selected properly (slightly higher than T_ai), the soft magnetic properties can remain relatively stable for a longer period of time.

The increase in H_c in the long-term annealed samples shown in Figure 8 and Figure 9 is also due to the formation of nanocrystalline clusters and the growth of these clusters. Figure 10 shows the smooth-side XRD patterns of the ribbons with different annealing times and temperatures for the Fe_81.4 and Fe_82.2 amorphous alloys. As shown in Figure 10, few weak diffraction peaks corresponding to the α-Fe crystalline phase can be detected in the smooth-side XRD patterns of the Fe_81.4 ribbons annealed at 633 K for 210 min and the Fe_82.2 ribbons annealed at 623 K for 150 min.

Figure 11 shows the magnetic domain structures of the as-spun, NA-623K-45 min-annealed and NA-623K-210 min annealed Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloy samples in the demagnetized state. Wide-curved domains and narrow fingerprint domains, caused by tensile stress and compressive stress [5,29], are observed in the as-spun Fe_82.2 amorphous alloy sample (Figure 11a). The domains of the sample annealing at 623 K for 45 min appear as a broad strip pattern oriented slightly away from the length direction of the amorphous ribbon, demonstrating the low domain energy, homogenous structure, and low stress state. However, for the sample annealed at 623K for 210 min, the magnetic domain structure with rugged edges can be clearly observed (Figure 11c), which is quite different from those in the NA-623 K-45 min annealed sample (Figure 11b). This indicates that a strong pinning effect exists, induced by partial crystallization resulting from long-term annealing (see Figure 10b) [5,9,27,32].

The above results indicate that when the annealing temperature is selected properly (slightly higher than T_ai), excellent and stable soft magnetic properties of amorphous alloys can be obtained through annealing even if the annealing is maintained for a very long time. Annealing slightly above T_ai could eliminate the influence of stress and the internal magnetic field on the H_c. In addition, a relatively low annealing temperature could reduce the possibility of crystallization. This result is of great significance for designing an annealing process for industrial applications.

4. Conclusions

The effects of annealing process parameters, including the annealing temperature and time, on the soft magnetic properties and magnetic domain structures of Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloys were systematically investigated, and the conclusions are summarized as follows:

(1)

Fe_81.4B_13.2C_2.8Si_1.8P_0.8 and Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloys were designed and prepared. This revealed that a lowest and highest temperature, denoted as T_a0 and T_am, respectively, exists for the optimum annealing of the amorphous alloys. The H_c of the Fe_81.4 and Fe_82.2 amorphous alloys annealed at T_a0–T_am for 90 min was 1.3–2.7 A/m, together with the B₈₀₀ of 1.64–1.66 T. T_a0 is determined by the variation in the magnetic properties with temperature. T_am is the temperature related to the crystallization of amorphous alloys.

(2)

It was found that on the B_s(T)–T curve, there is a temperature T_ai at which the dB_s/dT begins to decrease rapidly, and B_s(T_ai)/B_s(5K) = 45%. When the amorphous alloys were annealed slightly above T_ai, the effect of the inner magnetic field generated by spontaneous magnetization on the relaxation behavior became very weak. That is, the temperature T_ai could be employed as a characteristic temperature. Slightly above T_ai, an optimized annealing temperature T_a0 for the Fe-based amorphous alloys with a relatively low Curie temperature, similar to the studied alloys, could be determined quickly.

(3)

When the annealing temperature was selected properly (slightly higher than T_ai), the soft magnetic properties of amorphous alloys could remain excellent and stable even if annealed for a very long time. The H_c of the Fe_82.2B_12.4C_2.8Si_1.8P_0.8 amorphous alloy annealed at T_a1 = 603 K was only 1.9 A/m, while the annealing time was extended to 330 min.