Influence of Al addition on structure and magnetic properties of nanocrystalline Fe65Co15Si5Nb3Cu1B11-xAlx alloys

Influence of Al addition on structure and magnetic properties of nanocrystalline Fe65Co15Si5Nb3Cu1B11-xAlx alloys

Journal of Non-Crystalline Solids 442 (2016) 29–33 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www...

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Journal of Non-Crystalline Solids 442 (2016) 29–33

Contents lists available at ScienceDirect

Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol

Influence of Al addition on structure and magnetic properties of nanocrystalline Fe65Co15Si5Nb3Cu1B11-xAlx alloys Ying Han, Zhi Wang ⁎, Yan-chao Xu, Zhong-yan Xie, Li-juan Li School of Science, Tianjin University, Tianjin 300072, PR China

a r t i c l e

i n f o

Article history: Received 22 January 2016 Received in revised form 1 April 2016 Accepted 2 April 2016 Available online xxxx Keywords: Nanocrystalline materials FeCo-based alloy Soft magnetic properties Temperature dependence of permeability

a b s t r a c t The microstructure and soft magnetic properties of amorphous and nanocrystalline Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys were investigated. Microstructure has been analyzed from XRD patterns and magnetic properties were mainly studied by the evolution of initial permeability (μi) from room temperature to 700 °C. It was found that adding a certain amount of Al in Fe65Co15Si5Nb3Cu1B11 alloy significantly decreases onset primary crystallization temperature Tx1 from 452 °C to 388 °C and increases the crystallized interval temperature ΔTx from 188 °C to 290 °C. However, with the Al adding, the Curie temperature of amorphous phase Tam c shows a decline tendency. After annealing at 550 °C, the alloy with x = 1 exhibited the maximum room-temperature μi, however, the most stable soft magnetic properties at elevated temperatures was found in the alloy with x = 3. Therefore, the (μi-T) curves of Fe65Co15Si5Nb3Cu1B8Al3 samples annealed at 520–580 °C were also investigated in detail. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Fe-based nanocrystalline alloys have several advantages over other classes of materials for soft magnetic applications. These include high initial permeability (μi), improved thermal stability compared with amorphous alloys and low core loss [1,2]. The lower Curie point of an amorphous matrix, Tam c , however, limits its high temperature applications. It is well know that partial substitution of Fe by Co in Finemet alloys could enhance the Curie temperature of amorphous phase [3–5], but superfluous Co doping into Finemet would damage the magnetic softness because of larger magnetostriction. Therefore, a small amount of Co doping into Finemet is expected for improving both room- and high-temperature magnetic softness. In nanocrystalline alloys, the substitution of Co for Fe can also raise the saturation magnetization substantially, but this effect is diminished when the alloy also contains Si [4–8]. Furthermore, a high Si content will decrease the amorphous forming ability of the alloy which is made by the alloy composition deviation from the eutectic point. Therefore, a small amount of Si content is necessary for improving magnetic softness of nanocrystalline alloy with low Co content. It is reported that addition of Al in Finemet alloys could exhibit a lower Hc and a higher permeability due to the reduction in K1 and ultimately improve soft magnetic properties [9,10]. However, the change in magnetic properties with B and Al variation in the FeCoNbCuSiB system and their correlation with the structure has not been studied systematically so far. In addition, the Curie temperature of the crystalline phase ⁎ Corresponding author. E-mail address: [email protected] (Z. Wang).

http://dx.doi.org/10.1016/j.jnoncrysol.2016.04.003 0022-3093/© 2016 Elsevier B.V. All rights reserved.

and the magnetization in annealed samples abruptly decreased, when there was more than 5 at.% of Al in the alloy [11]. Therefore, a certain amount of Al was selected for partly substituting B in Fe65Co15Si5Nb3Cu1B11 alloy and a series of Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys were fabricated. In present research, the influence of Al addition on the microstructure and magnetic properties at roomand high-temperatures of FeCo-based Finemet-type alloys was mainly investigated. 2. Experimental procedures Amorphous ribbons of 0.8–1 mm wide and about 30 μm thick, were obtained by the single-roller melt spinning method with nominal composition Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3). The systematic errors were mainly obtained by material purity (99.99%) and measuring instrument precision (0.0001 g). The toroidal samples with an outer diameter of about 18 mm and inner diameter of about 16.3 mm were fabricated by winding the ribbons into toroidal cores. To obtain the characteristic nanocrystalline structures, samples were submitted to isothermal annealing at 520–580 °C for 0.5 h under vacuum atmosphere. The phase structure of 550 °C-annealed ribbons was examined by x-ray diffraction (XRD) using D/max-2500/PC with Cu-Kα radiation (λ = 1.54056 Å). The initial permeability μi was in situ measured by HP4294A impedance analyzer at H = 0.4 A/m, f = 10 kHz and a heating rate of 10 °C/min under Ar atmosphere protection over the temperature range of 30–700 °C. The systematic errors mainly produced by temperature deviation were estimated about 5%. The saturation magnetization Bs was measured by vibrating sample magnetometer (VSM). The crystallization temperature of amorphous ribbons (Tx) was determined by

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Fig. 1. DSC curves and crystallization temperatures of as-quenched Fe65Co15Si5Nb3Cu1B11(x = 0, 1, 2, 3) alloys.

xAlx

Table 1 Values of the onset primary and secondary crystallization temperatures (Tx1 and Tx2), the interval temperature ΔTx (ΔTx = Tx2-Tx1), as well as the Curie temperature (Tam c ) for asquenched Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys. Alloys

Tx1/°C

Tx2/°C

ΔTx/°C

Tam c /°C

x=0 x=1 x=2 x=3

451.9 ± 0.8 438.2 ± 0.8 433.3 ± 0.7 388.4 ± 0.6

639.9 ± 0.6 655.9 ± 0.7 650.3 ± 0.7 678.0 ± 0.7

188 ± 1.4 218 ± 1.5 217 ± 1.4 290 ± 1.3

410 ± 2 390 ± 2 380 ± 1 360 ± 1

the differential scanning calorimetry (DSC) with a heating rate of 10 °C/ min from room temperature to 1000 °C. 3. Results and discussion Differential scanning calorimetry (DSC) thermograms performed at 10 °C/min for the as-quenched Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys are shown in Fig. 1. For all samples, two separated exothermic peaks, which correspond to the two-stage crystallization process, were observed. The first one is correlated to the α-FeCo(AlSi) formation which is soft magnetic phase and the secondary one is associated with the subsequent precipitation of Fe B hard magnetic phase. The onset primary temperature (Tx1), secondary crystallization temperature (Tx2) for as-quenched and the interval temperature (ΔTx) Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys are shown in Table 1.

As is shown, the Tx1 shows a reduced tendency with increasing Al content. Especially for the alloy with x = 3, it exhibits a lowest Tx1 (~ 388 °C), which is lower than other Fe-based or FeCo-based alloys ever reported [3,12] and indicating its potential applications in technology. Although Tx2 and ΔTx shows an unstable change with adding Al, they exhibit general enlarged tendency compared with the Al-free alloy. Particularly, the alloy with x = 3 owns the largest ΔTx about 290 °C, which provides the possibility of precipitating a single soft magnetic crystalline phase from amorphous matrix in a broad temperature range. Fig. 2 (a) shows the μi-T curves of as-quenched Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys. A characteristic sharp Hopkinson peak was observed on all μi-T curves at the Curie point of am the amorphous phase, Tam c , from which we can get Tc = 410, 390,380 and 360 °C for the samples with x = 0, 1, 2, 3, respectively (see Table 1). The Curie temperature of amorphous phase (Tam c ) extracted from the μi-T curves of Fig. 2. (a) is shown in Fig. 2. (b). It can be observed that Tam c decreased drastically from 440 °C to 360 °C with Al content increasing from x = 0 to x = 3. Panda et al. [13] clearly reported that the Curie temperature of Fe-based alloys was not strongly dependent on the metalloid, and we assumed this theory is also applied to FeCo-based alloys. Therefore, it can be deduced that the significant decrease in is attributed to an increase of Al concentration in amorphous Tam c phase. Recently, Jia et al confirmed that Ni addition could decrease the of FeCo-based Finemet-type alloy because of Ni consuming an Tam c amount of Fe in amorphous phase and ultimately diminishing the stronger exchange interaction between Fe and Co atoms largely [12]. The results of our experiment indicate that Al had a similar action with Ni on of FeCo-based Finemet-type alloy, and we can also deduce that Tam c some metallic element could reduce Tam c in FeCo-based Finemet-type alloys. The initial permeability μi, as a structure-sensitive property, is an important parameter for the magnetic circuit design of electronic device. In order to analyze the effect of Al content on μi behavior of the alloys, μi–T curves of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys are shown in Fig. 3. For all the samples, the Hopkinson peak vanishes when they are annealed at 550 °C, indicating the formation of desired two-phase nanocrystal structure. The μi of samples with different Al content decreased at different rates around at Tam c . For the alloys with x = 0 and x = 2, the similar characteristic is that μi decreased toward zero near at their Tam c , although the falling rate of μi for alloy with x = 2 is relatively slower than that of Al-free alloy. It can be observed that the 550 °C-annealed Fe65Co15Si5Nb3Cu1B10Al1 alloy exhibited the maximum room-temperature μi (~ 2200), and the obvious difference compared with the above two alloys is that μi did not decrease to zero around Tam c but maintained a certain value until about T = 650 °C, which indicates its improved high-temperature soft

Fig. 2. (a) μi-T curves of as-quenched Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys. (b) The dependency of Tam c , extracted from the μi-T curves of Panel (a), on Al content for Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys.

Y. Han et al. / Journal of Non-Crystalline Solids 442 (2016) 29–33

Fig. 3. μi-T curves of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys.

magnetic properties. In comparison with the above three alloys, the 550 °C-annealed Fe65Co15Si5Nb3Cu1B8Al3 alloy shows the most stable value of μi, although the room-temperature μi is relatively lower (~ 1100), the falling rate of μi is rather slower and the hightemperature μi is no less than that of Fe65Co15Si5Nb3Cu1B10Al1 alloy. In addition, with the Al content increasing, the room-temperature μi first increases from 1700 (x = 0) to maximum value of 2200 (x = 1) and then decreases to 1100 (x = 3), the reason will be discussed in next part. In order to study the correlation between the microstructure and the magnetic properties of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys, XRD experiments were conducted as shown in Fig. 4. For all the annealed samples, the characteristic (110), (200) and (211) diffraction peaks corresponded to α-FeCo(SiAl) crystalline precipitates were observed. In addition, no peak corresponding to borides was detected (see Fig. 4(a)). Therefore, the microstructure of all the 550 °C-annealed samples consists of the residual amorphous phase and the nanocrystalline phases. Fig. 3(b) shows the enlarged XRD patterns of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys. It can be seen that, with Al content increasing, the diffraction peak intensity increases indicating a higher crystalline volume fraction (Vcry), which is an important positive factor for obtaining an improved high-temperature magnetic softness.

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Fig. 5. Average grain size D and room-temperature μi (extracted from the Fig. 3) dependence of Al content for 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys.

It has been reported that when the thickness of the intergranular amorphous layer d reaches a sufficient low value, the exchange coupling between the ferromagnetic nanocrystallites will penetrate through the thin paramagnetic amorphous layer, the higher the Vcry is, the thinner the layer, and then the stronger the penetrating transmission ability [14–17]. Therefore, for the 550 °C-annealed Fe65Co15Si5Nb3Cu1B8Al3 alloy, even the temperature being above Tam c , the stronger penetrating transmission ability still exists between the ferromagnetic nanocrystallites and thus the stronger exchange interaction of Fe Co atom pairs ultimately guarantees μi a certain value at high temperatures. Fig. 5 shows the average grain size (D), room-temperature initial permeability (μi) dependence of Al content for 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys. The average grain size (D) was estimated by means of the Scherrer formula from the full width at half maximum (FWHM) of the (110) peak of α-FeCo(SiAl). The maximal random errors mainly produced by the determination of location for the (110) peak of α-FeCo(SiAl) were estimated about 2%. It can be observed from Table 2 that the lattice parameter ( ) nearly keeps a constant value with Al increase, which is similar with that of nominal composition BCC Fe50Co50 single crystal (a = 0.2855 nm). While, the D decreases with x from about 22 nm at x = 0 to 21 nm at x = 1 and then increases to about 30 nm at x = 3. Besides, the roomtemperature initial permeability increases from about 1700 (x = 0) to maximum value of 2200 (x = 1) and finally decreases to about 1100 (x = 3). The interpretation of this change for the room initial permeability of 550 °C annealed samples can be based on Herzer's model which is expressed as [18]: μi∝

Ms2 μ 0 ðbK N þ 3=2λs σ Þ

ð1Þ

Where Ms is the saturation magnetization, σ is the residual stress, bKN is the effective magnetocrystalline anisotropy, λs is the saturation

Table 2 Average grain size (D), the lattice parameter ( ) and saturation magnetic induction (Bs) for 520–580 °C-annealed Fe65Co15Si5Nb3Cu1B8Al3 alloys and 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2) alloys.

Fig. 4. (a) XRD patterns of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys. (b) The enlarged patterns of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys.

Alloys

Ta/°C

D/nm

a/Å

Bs/T

Fe65Co15Si5Nb3Cu1B11 Fe65Co15Si5Nb3Cu1B10Al1 Fe65Co15Si5Nb3Cu1B9Al2 Fe65Co15Si5Nb3Cu1B8Al3

550°C 550°C 550°C 550°C 520°C 580°C

22.2 ± 0.4 21.1 ± 0.4 27.0 ± 0.5 29.2 ± 0.6 … …

2.855 ± 0.006 2.852 ± 0.006 2.853 ± 0.006 2.853 ± 0.006 … …

1.56 ± 0.01 1.54 ± 0.01 1.53 ± 0.01 1.53 ± 0.01 1.50 ± 0.01 1.47 ± 0.01

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Fig. 6. CharacteristicHBhysteresis loops of 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys, measured at room temperature, with an applied field of 10,000 A/m.

magnetostriction constant and μ0 is the vacuum permeability. It is well known that Ms is positive correlation with the saturation magnetic induction (Bs). To explore the main reason for evolution of μi with Al content, the Bs of 550 °C-annealed alloys was measured and shown in Fig. 6 and Table 2. It can be seen that the Bs first decreased from about 1.56 T (x = 0) to 1.54 T (x = 2) and then 1.53 T (x = 3) with Al content increasing. For the alloys with x = 0, 1, and 2, the average grain size D is small enough (less than 30 nm) and the magnetocrystalline anisotropy could be averaged out, therefore, the room initial permeability majorly lies on the contribution of Ms and λs. Based on the above analysis, the 550 °C-annealed Fe65Co15Si5Nb3Cu1B10Al1 alloy with a higher roomtemperature μi is most probably due to a faster decrease of λs than that of Ms. With respect to 550 °C-annealed Fe65Co15Si5Nb3Cu1B8Al3 alloy, although the room-temperature μi decreases largely, which may not only due to its relatively lower Ms but also because of the larger grain size (D) resulting in the larger magnetic anisotropy, the high temperature initial permeability maintains a certain value owing to its larger Vcry and exhibits a good thermal stability. Consequently, Fe65Co15Si5Nb3Cu1B8Al3 alloy is most likely to be an affordable material for high-temperature application. In order to further investigate the soft magnetic properties of alloys, the μi-T curves of Fe65Co15Si5Nb3Cu1B8Al3 Fe65Co15Si5Nb3Cu1B8Al3 alloys annealed at 520–580 °C are shown in Fig. 7. For 520–580 °C-annealed samples, the sharp Hopkinson peaks vanished indicating that the desired dual-phase nanostructure has been formed. Although the room-temperature μi has different values,

Fig. 7. μi-T curves of Fe65Co15Si5Nb3Cu1B8Al3 alloy annealed at 520–580 °C.

Fig. 8. XRD pattern of 580 °C-annealed Fe65Co15Si5Nb3Cu1B8Al3 alloy.

the μi decreased at a roughly similar rate from room temperature up to about T = 600 °C, which is different from other FeCo-based alloys ever reported [19]. According to Suzuki's random anisotropy model expressed as [20]:

bK N ¼

1 1 ð1−V am Þ−1=3 6 4 4 6 ffiffiffiffiffiffiffiffi p pffiffiffiffiffiffiffiffi ð 1−V Þ K D þ  am 1 φ6 Aam Acry

ð2Þ

Where b K N is the effective magnetocrystalline anisotropy, K1 the magnetocrystalline anisotropy, Vam the amorphous volume fraction, φ the spin rotation angle over the exchange correlation length, Aam and Acry are the exchange stiffness of amorphous and crystalline phase respectively. As the temperature approaches Tam c , considering that Aam drops to a much smaller value than Acry, therefore, the bK N increases rapidly with the continuous decline of Aam/Acry. Based on this theory, the μi-T curves of 520–580 °C-annealed samples display a decline tendency with T. Furthermore, the increasing rate of b KN is closely related to Vcry, the higher the Vcry is, the smaller the increasing rate of b KN. Now, the μi-T curves of three annealed alloys show a similar decline rate, which suggested that the three samples annealed at different temperature own the similar Vcry and the soft magnetic crystalline phase has precipitated completely when Ta reached 520 °C. Besides, for 520–580 °C-annealed samples, the room-temperature μi first increased

Fig. 9. CharacteristicHB hysteresis loops of Fe65Co15Si5Nb3Cu1B8Al3 alloys annealed at 520–580 °C, measured at room temperature, with an applied field of 10,000 A/m. The inset shows the enlarged hysteresis loop.

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from ~800 (Ta = 520 °C) to ~1100 (Ta = 550 °C) and then decreased to ~700 (Ta = 580 °C) with annealing temperature increasing. To explain the change of room-temperature μi with annealing temperature, XRD B hysteresis pattern of 580 °C-annealed Fe65Co15Si5Nb3Cu1B8Al3 alloy, H loops and the values of Bs for Fe65Co15Si5Nb3Cu1B8Al3 alloys annealed at 520–580 °C were shown in Figs. 8 and 9 and Table 2 respectively. It can be observed from Fig. 8 that no obvious characteristic diffraction peak for Fe2B hard magnetic phase is detected. Therefore, the reason for the decrease of μi for 580 °C-annealed sample is most probably be ascribed to both the change of Ms and λs of the alloy with temperature. According to Table 2 and the enlarged hysteresis loop of Fig. 9, for 520–580 °C-annealed samples, the Bs first increased from 1.50 T (Ta = 520 °C) to 1.53 T (Ta = 550 °C) and then decreased to 1.47 T (Ta = 580 °C), which is in keep with the change of room-temperature μi with different annealing temperature. Therefore, the Ms played a decisive role in the change of room-temperature μi with different annealing temperature. 4. Conclusions In Fe65Co15Si5Nb3Cu1B11 alloy, replacing B with a small amount of Al can decrease primary crystallization temperature Tx1 from 452 °C to 388 °C and increases the crystallized interval temperature ΔTx from 188 °C to 290 °C, which is favorable to precipitating single soft magnetic crystal phase from amorphous matrix in a wide temperature range. There was a general reduced tendency of Tam c with Al content increasing, which may be due to Al diminishing the stronger exchange interaction between Fe and Co atoms in FeCo-based Finemet-type alloy. All the 550 °C-annealed Fe65Co15Si5Nb3Cu1B11-xAlx (x = 0, 1, 2, 3) alloys can form α-FeCo(SiAl) nanocrystalline phase embedded in residual amorphous matrix. It was found that, although the 550 °C-annealed Fe65Co15Si5Nb3Cu1B10Al1 exhibited the maximum room-temperature μi, Fe65Co15Si5Nb3Cu1B8Al3 alloy is most likely to be an affordable material for high-temperature application owing to its larger Vcry and good

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thermal stability. Annealing temperature had a significant effect on room- and high-temperature initial permeability μi of the Fe65Co15Si5Nb3Cu1B8Al3 alloys annealed at 520–580 °C, which is most probably attributed to the change in Ms. Acknowledgements This work was supported by National Natural Science Foundation of China (under Grant no. 51271130). References [1] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [2] M.M. Raja, K. Chattopadhyay, B. Majumdar, A. Narayanasamy, J. Alloys Compd. 297 (2000) 199. [3] Ye-mei Han, Zhi Wang, Xiang-hui Che, Xue-gang Chen, Wen-run Li, Ya-li Li, Mater. Sci. Eng. B 156 (2009) 57–61. [4] S. Bhattacharya, E.A. Lass, S.J. Poon, et al., J. Alloys Compd. 488 (79) (2009). [5] S. Bhattacharya, E.A. Lass, S.J. Poon, et al., J. Appl. Phys. 111 (2012) 063906. [6] A. Kolano-Burian, J. Ferenc, T. Kulik, Mater. Sci. Eng. A 375–377 (2004) 1078–1082. [7] M. Muller, H. Grahl, N. Mattern, U. Kuhn, B. Schnell, J. Magn. Magn. Mater. 160 (1996) 284–286. [8] Y. Yoshizawa, S. Fujii, D.H. Ping, M. Ohnuma, K. Hono, Mater. Sci. Eng. A 375–377 (2004) 207–212. [9] I. Todd, B.J. Tate, H.A. Davies, et al., J. Magn. Magn. Mater. 215-216 (2000) 272–275. [10] S.H. Lim, W.K. Pi, T.H. Noh, H.J. Kim, I.K. Kang, J. Appl. Phys. 73 (1993) 6591. [11] A. Zorkovska, J. Kovac, P. Sovak, et al., J. Magn. Magn. Mater. 215–216 (2000) 492–494. [12] Y.-Y. Jia, Z. Wang, R.-M. Shi, J. Yang, H.-J. Kang, T. Lin, J. Appl. Phys. 109 (2011) 073917. [13] A.K. Panda, B. Ravilumar, S. Basu, et al., J. Magn. Magn. Mater. 260 (2003) 70–77. [14] X.H. Ma, Z. Wang, X.T. Han, et al., Mater. Sci. Eng., A 448 (216) (2007). [15] X.Y. Zhang, F.X. Zhang, J.W. Zhang, et al., J. Appl. Phys. 84 (1998) 1918–1923. [16] J. Wang, Z. Wang, Y.-Y. Jia, et al., J. Appl. Phys. (2013), 17A310. [17] Y. Han, Z. Wang, J. Non-Cryst. Solids 434 (2016) 92–95. [18] G. Herzer, Scr. Metall. Mater. 33 (1741) (1995). [19] Y.-Y. Jia, Z. Wang, J. Wang, et al., J. Magn. Magn. Mater. 324 (2012) 3981–3985. [20] K. Suzuki, J.M. Cadogan, Random magnetocrystalline anisotropy in twophasenanocrystalline systems, Phys. Rev. B 58 (1998) 2730.