The Thermal and Magnetic Properties of the Fe89.8Ni1.5Si5.2B3C0.5 and Fe81B13Si14C2 Amorphous Alloys

This paper investigates the thermal and magnetic properties of two iron based amorphous alloys with different Fe-content: Fe89.8Ni1.5Si5.2B3C0.5 and Fe81B13Si14C2. The XRD results show that the thermal induced structural changes occur in the temperature range of 300C – 850C for the Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy. The appearance of the first crystallization peaks on DSC thermograms of Fe81B13Si4C2, amorphous alloy is perceived already at 450C. The initial magnetization curves of the as-cast sample of the Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy, obtained at the frequencies of 50 Hz, 400 Hz and 1000 Hz show the excellent match. The maximum relative magnetic permeability for Fe89.8Ni1.5Si5.2B3C0.5 alloy sample is achieved at magnetic field strength of about 20 A/m for all frequencies, whereas the values of about 7000 were obtained at the frequencies of 50 Hz and 400 Hz. The influence of frequency on total power losses, for both alloys exhibits the increase of core losses with frequency increase. The amorphous alloy Fe89.8Ni1.5Si5.2B3C0.5 toroidal core exhibits about 3 time higher total power losses.


Introduction
Iron based amorphous and nanocrystalline alloys are well established commercial soft-magnetic materials as their properties ratio vs. prices is well acceptable in common electrical devices.There are still intensive research efforts of their sensors effects as a single used ribbon [1,2] or as a combination of amorphous ribbon with piezofiber [3,4] or magnetostrictive [5] laminates as a new generation of multifunctional materials.Metglas/PMN-PT fiber laminates as an excellent magnetoelectric composite for low noise sensor of ultralow magnetic field were presented at operating frequency f = 1 Hz [3].
Also, the investigations with two interesting goals are still actually due to reducing size of transformers: the increase of magnetic induction and decrease of coercive force [6,7], i.e. the improvement of permeability and power losses.The first task was solved with the increasing atomic percentage of the iron content, i.e. with the substantial iron content over 80% that is the most probably position of the eutectic minimum in Fe-M (M-metalloid) systems.
Iron based nanocrystalline alloys exhibit excellent soft magnetic properties, low coercivity, high permeability and therefore low power losses [8].For instance, there is very perspective commercial alloy Fe 81.2 Co 4 Si 0.5 B 9.5 P 4 Cu 0.8 NANOMET with core losses of about 0.15 W/kg at 50 Hz and at 0.6 T [9].Interesting soft magnetic properties of MnZn ferrites were obtained by optimization of powder injection molding technology [10]; however these ferrites have low values of saturation magnetic induction B s .
In this paper is presented the comparison of magnetic properties of two iron based amorphous alloys with different Fe-content.The first alloy is the commercial composition Fe 81 B 13 Si 14 C 2 and the second one is the alloy with significantly increased iron content Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 .

Experimental
Ribbon shaped samples of the investigated amorphous alloys were obtained using the standard procedure of rapid quenching of the melt on a rotating disc (melt-spinning).The obtained ribbons were 2 cm wide and 35 μm thick.Thermal stability was investigated in a nitrogen atmosphere by the differential scanning calorimetry method (DSC) using SHIMADZU DSC-50 analyzer in the temperature region from room temperature to 600 0 C. Xray investigations were performed using Cu-K α radiation lines (λ = 0.154178 nm) on a Phillips PW1710 device.B-H hysteresis loops were measured on toroidal core samples at different frequencies of sinusoidal excitation and at different magnetic fields for both alloys by Brockhaus MPG 100D measuring system.

Results and discussion
In our previous papers [11,12] it was shown that the amorphous alloy Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 crystallizes within the temperature range from 520 0 C to 620 0 C. Therefore, the process of the structural relaxation was studied at temperatures for 100 -150 0 C lower than the initial crystallization temperature.XRD patterns of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 and Fe 81 B 13 Si 14 C 2 samples are shown in the diagrams on Fig. 1.Fig. 1a shows XRD difractograms of the as-cast samples and samples annealed at 300 0 C and 540 0 C for 60 minutes of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 alloy.Annealing of alloy samples were performed in quartz ampoule which were further vacuumed and isothermally treated for 60 minutes.Based on the wide peak in the range of the diffraction angles 2θ of 40 0 -50 0 , it may be determined that the as-cast Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 (Fig. 1a) and Fe 81 B 13 Si 14 C 2 (Fig. 1b) alloy samples are characterized by high level of amorphousness.Due to presence of small percentage of matalloides (Si, B, C below 10%), as-cast samples are not fully amorphous, as amorphous matrix features residual crystallites upon obtaining.Amorphous structure remains unchanged during the alloy heating at 300 0 C (Fig. 1a).For better understanding of the crystallization process, the analysis of the X-ray difractogram of Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 alloy samples was conducted, which had been isothermally heated in the temperature range from 300 0 C to 850 0 C, showing that the thermal induced structural changes occur in this temperature region.Fig. 1b shows the X-ray difractograms of the as-cast samples and samples annealed at 450 0 C and 700 0 C during 60 minutes of the alloy Fe 81 B 13 Si 14 C 2 .Amorphous structure remains unchanged at annealing of this alloy at the temperature of 400 0 C [13].The appearance of the first crystallization peaks on difractograms of Fe 81 B 13 Si 4 C 2 alloy samples is perceived at 450 0 C [14].Hysteresis B-H loops has been monitored for the as-cast Fe 81 B 13 Si 4 C 2 torusshaped alloy samples as well.The frequency effect on hysteresis loops at H max = 100 A/m and the sinusoidal excitation of 50, 200, 400, 600, 800 and 1000 Hz is shown on Fig. 6 [14].
As it can be observed from the Fig. 5 and Fig. 6, the hysteresis loops become wider and magnetic losses increase with frequency increase.Such dependence is caused by eddy currents and at higher frequencies by spin relaxation processes.It can be noticed on Fig. 6 that hysteresis loops of the Fe 81 B 13 Si 4 C 2 alloy have higher remanence ratio (B r /B s ≈ 0.8), that is a significant advantage of this magnetic material for the application in electrical devices.Further, the significant increase of iron content in amorphous alloy Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 is followed with the increase of coercivity.It can be noticed on Fig. 8 that the hysteresis loops of the as-cast Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 alloy sample get wider with the increase in frequency, while the increase in the surface area of these loops results in the increased power core losses.
The total core losses are proportional to the surface area of hysteresis loop and consist of two components: hysteresis losses P h and eddy current losses P e , i.e.P s = P h + P e.
Hysteresis losses are proportional to the frequency (~ f): where: η -Steinmetz hysteresis coefficient, f -frequency, B m -maximum magnetic flux density, m -toroidal corre mass.Eddy-current losses are proportionally to the square of frequency (~ f 2 ): where σ is parameter that involve thickness, resistivity and density of material.The comparison of the frequency dependence of total power losses P s referred to the core mass for both investigated alloys is shown on Fig. 9.As it can be noticed the Fe 81 B 13 Si 4 C 2 amorphous alloy toroidal core exhibits about 3 times lower total power losses.The significant increase of iron content in the amorphous alloy Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 is followed with the increase of coercivity as a result of more intensive magnetic domain pinning effect and therefore with the increase of total core power losses.
Total core losses of the amorphous alloy Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 are 0.8 W/kg at 50 Hz and at 0.54 T that is 2 times higher in comparison with commercially non-oriented magnetic steel [9].

Conclusion
The comparison of magnetic properties of two iron based soft magnetic amorphous ribbons with different Fe-content was perfomed.The first alloy is the commercial composition Fe 81 B 13 Si 14 C 2 and the second one is the alloy with significantly increased iron content Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 .The initial magnetization curves of the as-cast sample of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 amorphous alloy, obtained at the frequencies of 50 Hz, 400 Hz and 1000 Hz show the excellent match.The maximum relative magnetic permeability for Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 alloy sample is achieved at magnetic field strength of about 20 A/m and the values of about 7000 are obtained at the frequencies of 50 Hz and 400 Hz.The hysteresis loops of both alloys become wider and therefore the core losses increase with frequency increase due to eddy currents and spin relaxation at higher frequencies.It can be noticed that hysteresis loops of the Fe 81 B 13 Si 4 C 2 alloy have higher remanence ratio (B r /B s ≈ 0.8) than the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 alloy (B r /B s ≈ 0.75), that is a significant advantage of this magnetic material for the application in electrical devices.The significant increase of iron content in the amorphous alloy Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 is followed with the increase of coercivity as a result of more intensive magnetic domain pinning effect and therefore with the increase of total core power losses.

Fig. 1 .Fig. 2 .
Fig. 1.XRD patterns of the a) Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 and b) Fe 81 B 13 Si 14 C 2 samples.The thermal stability of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5[12] and Fe 81 B 13 Si 4 C 2 alloy samples was investigated by DSC in the temperature interval of 20 0 C -600 0 C, at the heating rate of 20 0 C/min.Fig.2shows DSC thermogram of the Fe 81 B 13 Si 4 C 2 as-cast alloy sample.

Fig. 3
Fig.3shows magnetization curves of the as-cast sample of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 amorphous alloy, obtained at the frequencies of 50 Hz, 400 Hz and 1000 Hz.As it can be noticed, all three curves exhibit the excellent match.

Fig. 3 .
Fig. 3.The initial magnetization curves of as-cast sample of Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 amorphous alloy at frequencies of 50 Hz, 400 Hz and 1000 Hz.

Fig. 4
Fig.4shows dependence of the relative magnetic permeability (μ r = μ/μ 0 ) over the external magnetic field strength at the frequencies of 50 Hz, 400 Hz and 1000 Hz for Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 as-cast amorphous alloy sample.Maximum relative magnetic permeability is achieved at magnetic field strength of about 20 A/m for all three frequencies, whereas the highest values of about 7000 are obtained at frequencies of 50 Hz and 400 Hz.

Fig. 4 .
Fig. 4. The relative magnetic permeability dependence on external magnetic field at frequencies of 50 Hz, 400 Hz and 1000 Hz.

Fig. 7 Fig. 7 .
Fig. 7.The hysteresis loops of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 toroidal sample in as-cast state at frequency of 50 Hz and at different magnetic fields (from 1000 A/m to 3000 A/m).

Fig. 8
Fig. 8 shows hysteresis loops of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 as-cast alloy sample, obtained at different frequencies of 50 Hz, 400 Hz and 1000 Hz and at different magnetic field strengths from 10 A/m to 100 A/m.

Fig. 8 .
Fig. 8.The hysteresis loops of the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 toroidal sample in as-cast state at frequencies of a) 50 Hz, b) 400 Hz and c) 1000 Hz and at different magnetic fields.

Fig. 9 .
Fig. 9.Total power losses P s referred to the core mass for the Fe 89.8 Ni 1.5 Si 5.2 B 3 C 0.5 and the Fe 81 B 13 Si 4 C 2 amorphous alloys.