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Electron-irradiation induced changes in structural and magnetic properties of Fe and Co based metallic glasses
Journal of Alloys and Compounds xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Electron-irradiation induced changes in structural and magnetic properties of Fe and Co based metallic glasses S.N. Kane a,⇑, M. Satalkar a, A. Ghosh a, M. Shah a, N. Ghodke b, R. Pramod c, A.K. Sinha c, M.N. Singh c, J. Dwivedi c, M. Coisson d, F. Celegato d, F. Vinai d, P. Tiberto d, L.K. Varga e a
School of Physics, D.A. University, Khandwa Road Campus, Indore 452001, India UGC-DAE CSR, University Campus, Khandwa Road, Indore 452001, India Raja Ramanna Centre for Advanced Technology, P.O. CAT, Indore 452013, India d INRIM, Electromagnetism Division, Strada Delle Cacce 91, I-10135 TO, Italy e RISSPO, Hungarian Academy of Sciences, P.O. Box 49, 1525 Budapest, Hungary b c
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Metallic glasses Electron irradiation Magnetic properties XRD RDF
a b s t r a c t Electron-irradiation induced changes in structural and, magnetic properties of Co57.6Fe14.4Si4.8B19.2Nb4, Fe72Si4.8B19.2Nb4 and, Co72Si4.8B19.2Nb4 metallic glasses were studied using magnetic hysteresis and, synchrotron X-ray diffraction measurements. Results reveal composition dependent changes of magnetic properties in electron irradiated metallic glasses. A low electron irradiation dose (15 kGy) enhances saturation magnetization (up to 62%) in Fe-based alloy (Fe72Si4.8B19.2Nb4). Synchrotron XRD measurements reveal that electron irradiation transforms the amorphous matrix to a more ordered phase, accountable for changes in magnetic properties. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Fe and Co-based metallic glasses exhibit superior magnetic properties which are sensitive to microstructure, composition and thermal treatments [1]. Microstructure can be modified by various thermal treatments to realize structural relaxation [2], partial crystallization [3], which in-turn will modify the magnetic properties [3]. Other treatments like – electron irradiation is known to induce solid-state amorphization of crystalline phases (in which nanocrystalline structures can not easily be obtained by conventional thermal annealing) [4] and, crystallization of an amorphous phase [5]. Studies on irradiation-induced changes in structure of metallic glasses are done with respect to their prospective application of amorphous alloys as radiation-resistant materials [6]. Electron irradiation is an efficient way to realize structural changes e. g. – crystallization of the amorphous phase. Control on amorphous to crystallization transformation is an important factor to have the soft magnetic behavior [3], which can be achieved by variation of electron irradiation dose. It has been demonstrated that electron irradiation can induce nanocrystallization in metallic glasses in which nanoscale structures can not be ⇑ Corresponding author. Tel.: +91 9893377409. E-mail addresses: [email protected] (S.N. Kane), [email protected] (M. Satalkar).
obtained easily by thermal annealing [4]. Fe and Co based amorphous and nanocrystalline alloys exhibit low coercivity, low losses and, superior saturation magnetization and are of use for various power applications. Increasing demand for better soft magnetic materials is one of the main driving force for optimizing magnetic properties of amorphous alloys via changes in composition and, post-preparation treatments (thermal treatments, electron irradiation etc.). Studies on electron irradiation induced changes in the structure of metallic glasses are reported [6,7], affecting their magnetic properties [7], via radiation-enhanced diffusion. However, reports on effect of electron irradiation on magnetic properties are rather limited [6,7]. Therefore in the present work, we report electron-irradiation induced changes in structural and magnetic properties of Co57.6Fe14.4Si4.8B19.2Nb4, Fe72Si4.8B19.2Nb4 and, Co72Si4.8B19.2Nb4 metallic glasses using magnetic hysteresis and, synchrotron X-ray diffraction measurements. 2. Experimental details Metallic glass Ribbons of nominal composition Co57.6Fe14.4Si4.8B19.2Nb4 (labelled as sample A), Fe72Si4.8B19.2Nb4, (labelled as sample B) and, Co72Si4.8B19.2Nb4 (labelled as sample C) were prepared by planar flow casting in air on a Cu wheel at Wigner Research Centre for Physics, Budapest (Hungary). Electron irradiation of the samples were done by using the electron irradiation facility available at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore (India). The specimens were surface treated at 700 keV electron beam energy and 1.5 mA beam current
http://dx.doi.org/10.1016/j.jallcom.2014.01.236 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: S.N. Kane et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.01.236
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S.N. Kane et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx
using a DC accelerator. The sample was placed on the conveyor system in air. The electron beam obtained from the accelerator is scanned in scan horn with frequency of 100 Hz. This scanned beam is transmitted in air through 50 lm titanium foil. The sample to be irradiated was placed 100 mm below the titanium foil in air. The elliptical beam of dimension 100 mm 120 mm falls on the sample. The sample was moved with velocity of 20 m/min. in the beam path. Five different electron doses – 15, 45, 75, 105 and 150 kilo Gray (kGy) were given to as-cast samples. Hysteresis loops of 80 mm long samples were measured using the conventional induction technique at 50 Hz [8], using a compensated pick-up coil pair (each containing 3000 turns) for field flux compensation. Magnetic field was applied by a 200 long solenoid containing 1651 turns. Maximum field (Hmax) ±1 kA/m was used for hysteresis measurements. Raw data corresponding to measured hysteresis loops was obtained by a digital storage oscilloscope and, was analyzed using a MatlabÒ based program, to obtain coercivity (Hc) and, saturation induction (Bs). X-ray Diffraction (XRD) experiments were carried out by using angle dispersive X-ray Diffraction (ADXRD) beamline BL-12 at 21 keV (17 keV for sample A) using Mar 345 image plate at Indus 2 Synchrotron Radiation Source, RRCAT, Indore (India). XRD data was analyzed to obtain Radial Distribution Function (RDF) to get information on electron-irradiation induced structural changes in the studied samples. RDF provides information on the distribution of elements in various coordination shells.
a
1.0
B (Tesla)
0.5
As-cast 15 kGy 45 kGy 75 kGy 105 kGy 150 kGy
Co57.6 Fe14.4 Si4.8 B19.2 Nb4
Sample A
0.0
-0.5
-1.0 -60
Integration between the adjacent minima gives the average number of neighbouring atoms in a coordination shell. Also various maxima show the most probable position for the atoms in that coordination shell. Here the first coordination shell shows the TM–TM distance (TM–Transition Metal). The TM–TM distance and, the average number of atoms in the coordination shell for as quenched and electron irradiated samples was calculated.
3. Results and discussions Fig. 1(a)–(c) respectively depicts the electron irradiation dose dependence of hysteresis loops in sample A, B and C. Perusal of Fig. 1 depicts the effect of variation of electron irradiation in the studied samples and, it is worth noting that the studied samples (whose compositions are different) respond differently to their exposure to difference in the electron dose. Fig. 2 depicts the electron irradiation dependence of coercivity (measured within the accuracy of 0.5 A/m) in samples A, B and C. Perusal of Fig. 2 depicts that, variation of specimen composition and, electron dose shows changes in coercivity (Hc), although one can not deduce a very clear trend in view of the scattering of the points. In sample A, Hc oscillates along an average constant value. For sample B, not much variation of Hc is observed (except for the point corresponding to the sample irradiated with 120 kGy dose). Sample C displays an Hc reduction after an irradiation with 15 kGy dose and, for higher doses it exhibits practically a constant value. Observed changes in Hc values are ascribable to the appearance of more ordered phase in the specimens via electron irradiation.
25 -40
-20
0
20
40
60
Sample A
H (A/m)
Sample B
20
0.5
B (Tesla)
Sample C Fe 72 B19.2 Si4.8 Nb4
As-cast 15 kGy 45 kGy 75 kGy 105 kGy 150 kGy
Hc (A/m)
b
1.0
Sample B
15
10
0.0
5 -0.5
0
40
80
120
160
Dose (kGy) -1.0 -60
Fig. 2. Electron irradiation dose dependence of coercivity in the studied samples.
-40
-20
0
20
40
60
H (A/m) 1.0
B (Tesla)
0.5
0.0
As-cast 15 kGy 45 kGy 75 kGy 105 kGy 150 kGy
Sample B,
Sample C
Sample C 1.0
-0.5
-1.0 -60
Sample A,
1.2
Co72 B19.2 Si4.8 Nb4
Bs (Tesla)
c
0.8
0.6
-40
-20
0
20
40
60
H (A/m) Fig. 1. Electron irradiation dose dependence of hysteresis loops: (a) sample A, (b) sample B and (c) sample C.
0.4
0
40
80
120
160
Dose (kGy) Fig. 3. Electron irradiation dose dependence of saturation induction in the studied samples.
Please cite this article in press as: S.N. Kane et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.01.236
3
a
10
Normalized Intensity
Intensity (Arb. Units)
S.N. Kane et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx
8
Sample C
Sample B Sample A 0
4
8
q = 4πsin (θ)/λ
12 (Α-1)
6 4 2 0
Fig. 4. Synchrotron XRD of the studied samples. Line/symbols are for electron irradiated/as cast samples.
2
4
6
8
10
12
q (1/Angstrom)
b
100 80
RDF
Fig. 3 shows the electron irradiation dependence of saturation induction in samples A, B and C. Perusal of Fig. 3 depicts a clear trend of Bs as a function of electron irradiation dose for the studied samples This behaviour can be understood in terms of the appearance of a more ordered phase with electron irradiation and, has strong dependence on specimen composition. Sample B (Fe-rich) exhibits increase of Bs with increase of electron irradiation dose, whereas sample C (Co-rich) displays decrease of Bs with increase of electron irradiation dose. Thus, Fe-rich (sample B) and Co-rich (sample C) samples show opposite behaviour of Bs with electron irradiation dose. But sample A which contains both Fe and Co shows intermediate behaviour, which can be seen very clearly in Fig. 3, ascribable to opposite effects of Fe and Co on Bs. It is interesting to note that in case of sample B, the Bs increase by 62% after electron irradiation with a dose of 15 kGy. Present results show that in Fe-based metallic glasses, a low electron irradiation dose (as low as 15 kGy) helps in increasing Bs, almost without any increase of Hc, whereas it works adversely for Co-based samples. Fig. 4 depicts the synchrotron XRD of the studied samples (line/ symbols are for electron irradiated/as cast samples). The structure of a monatomic amorphous sample in real space can be described by pair distribution function g(r), which is proportional to the probability of finding an atom at a position r relative to the reference atom taken at the origin. Radial Distribution Function (RDF), related to g(r) by the relation RDF = 4prq0g(r), has been calculated by Fourier transform of normalized and corrected X-ray scattering data. Since the technique is based on the Fourier transform, large q measurements are needed for a reasonable result. Therefore, we have done calculations for only sample B and sample C. The details of the calculations are given in [9]. We have done calculations in the frame work of monatomic sample; although our sample is polyatomic. This can be justified because the only major scatterers in our samples are Transition Metal (TM). Other scatterers are either low Z (Si and B) or very small in quantity (Nb). Therefore, we have done the calculations in the framework of monatomic sample. This is in agreement with a recent publication [10], where similar arguments were given. Corrected and normalized X-ray diffraction data (Fig. 5(a)) and RDF (Fig. 5(b)) are given for sample C. The fit parameters for the first coordination shell are shown in Table 1, for samples B and C (as quenched as well as electron irradiated). A closer look at Table 1 shows that TM–TM distance do not show appreciable changes and, almost remains the same (1.64 ± 0.1 Å) for sample B, whereas, it decreases for sample C; on electron irradiation. The width of the first coordination shell, however, decreases considerably for both the samples on electron irradiation. The decrees of width clearly indicate that the amorphous matrix is transforming to more ordered phase on electron irradiation, showing noticeable changes in Bs values and also a strong compositional dependence, especially for sample B and C, as can be seen in Fig. 3. More studies on various other samples
0
60 40 20 0 0
2
4
6
8
10
r (Angstrom) Fig. 5. (a) Corrected and normalized X-ray diffraction data and (b) RDF for sample C.
Table 1 TM–TM distance and the average number of atoms in the coordination shell for as quenched and electron irradiated samples. Sample details
TM–TM distance (Å)
Average number of atoms in the first coordination shell
Width of the first coordination shell
Sample C (as quenched) Sample C (electron irradiated) Sample B (as quenched) Sample B (electron irradiated)
2.62 2.59 2.65 2.63
11.39 12.61 12.92 13.61
1.07 0.55 1.1 0.52
and other treatments like thermal annealing need to be carried out to work out in order to establish a definitive correlation between structural and magnetic properties. To summarize, studied samples which have differences in composition, respond differently to electron irradiation. Results show that variation in composition show changes in coercivity. Low electron irradiation dose of 15 kGy enhances saturation magnetization up to 62% in specimen B. Synchrotron XRD measurements indicate that the amorphous matrix is transforming to more ordered phase on electron irradiation, ascribable to the observed changes in magnetic properties.
Acknowledgements This work is supported by Indo–Portuguese joint project No. Int/Portugal/P-07/2013. MS (Research fellowship recipient) is supported by UGC-DAE CSR, Indore project CSR-I/CRS51/2011-12]. AG
Please cite this article in press as: S.N. Kane et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.01.236
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S.N. Kane et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx
is financially supported by UGC, Dr. D.S. Kothari Postdoctoral Fellowship scheme [F. 4-2/2006(BSR)/13-565/2011(BSR)]. References [1] S.N. Kane, S. Tripathi, M. Coisson, E.S. Olivetti, P. Tiberto, F. Vinai, M. Baricco, G. Fiore, A. Apolinário, C.T. Sousa, J.P. Araujo, L.K. Varga, J. Alloys Comp. 537 (2012) S337. [2] G.P. Tiwari, R.V. Ramanujan, M.R. Gonal, R. Prasad, P. Raj, B.P. Badguzar, G.L. Goswami, Mater. Sci. Eng. A 304–306 (2001) 499. [3] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044.
[4] M. Sorescu, E.T. Knobbe, D. Barb, Phys. Rev. B 51 (1995) 840. [5] H. Chiriac, F. Rusu, J. Magn. Magn. Mater. 196–197 (1999) 156. [6] T. Nagase, Y. Umakoshi, Mater. Trans. 46 (2005) 616; A. Nino, T. Nagase, Y. Umakoshi, Mater. Trans. 46 (2005) 181. [7] T. Nagase, Y. Umakoshi, ISIJ Int. 46 (2006) 1371. [8] S.N. Kane, Z. Gercsi, N. Ghodke, S.S. Khinchi, A. Gupta, in: V.K. Aswal, K.G. Bhushan, J.V. Yakhmi (Eds.), Proc. of the DAE Solid State Physics Symposium, vol. 50, Prime Time Education, Mumbai, 2005, pp. 287–288 (ISBN 81-8372019-6). [9] H.E. Fisher, A.C. Barnes, P.S. Salmon, Rep. Prog. Phys. 69 (2006) 233. [10] P. Gupta, T. Ganguly, A. Gupta, A.K. Sinha, S.K. Deb, P. Svec Jr., Franco, J. Appl. Phys. 111 (2012) 113518.
Please cite this article in press as: S.N. Kane et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.01.236
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Electron-irradiation induced changes in structural and magnetic properties of Fe and Co based metallic glasses S.N. Kane a,⇑, M. Satalkar a, A. Ghosh a, M. Shah a, N. Ghodke b, R. Pramod c, A.K. Sinha c, M.N. Singh c, J. Dwivedi c, M. Coisson d, F. Celegato d, F. Vinai d, P. Tiberto d, L.K. Varga e a
School of Physics, D.A. University, Khandwa Road Campus, Indore 452001, India UGC-DAE CSR, University Campus, Khandwa Road, Indore 452001, India Raja Ramanna Centre for Advanced Technology, P.O. CAT, Indore 452013, India d INRIM, Electromagnetism Division, Strada Delle Cacce 91, I-10135 TO, Italy e RISSPO, Hungarian Academy of Sciences, P.O. Box 49, 1525 Budapest, Hungary b c
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Metallic glasses Electron irradiation Magnetic properties XRD RDF
a b s t r a c t Electron-irradiation induced changes in structural and, magnetic properties of Co57.6Fe14.4Si4.8B19.2Nb4, Fe72Si4.8B19.2Nb4 and, Co72Si4.8B19.2Nb4 metallic glasses were studied using magnetic hysteresis and, synchrotron X-ray diffraction measurements. Results reveal composition dependent changes of magnetic properties in electron irradiated metallic glasses. A low electron irradiation dose (15 kGy) enhances saturation magnetization (up to 62%) in Fe-based alloy (Fe72Si4.8B19.2Nb4). Synchrotron XRD measurements reveal that electron irradiation transforms the amorphous matrix to a more ordered phase, accountable for changes in magnetic properties. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Fe and Co-based metallic glasses exhibit superior magnetic properties which are sensitive to microstructure, composition and thermal treatments [1]. Microstructure can be modified by various thermal treatments to realize structural relaxation [2], partial crystallization [3], which in-turn will modify the magnetic properties [3]. Other treatments like – electron irradiation is known to induce solid-state amorphization of crystalline phases (in which nanocrystalline structures can not easily be obtained by conventional thermal annealing) [4] and, crystallization of an amorphous phase [5]. Studies on irradiation-induced changes in structure of metallic glasses are done with respect to their prospective application of amorphous alloys as radiation-resistant materials [6]. Electron irradiation is an efficient way to realize structural changes e. g. – crystallization of the amorphous phase. Control on amorphous to crystallization transformation is an important factor to have the soft magnetic behavior [3], which can be achieved by variation of electron irradiation dose. It has been demonstrated that electron irradiation can induce nanocrystallization in metallic glasses in which nanoscale structures can not be ⇑ Corresponding author. Tel.: +91 9893377409. E-mail addresses: [email protected] (S.N. Kane), [email protected] (M. Satalkar).
obtained easily by thermal annealing [4]. Fe and Co based amorphous and nanocrystalline alloys exhibit low coercivity, low losses and, superior saturation magnetization and are of use for various power applications. Increasing demand for better soft magnetic materials is one of the main driving force for optimizing magnetic properties of amorphous alloys via changes in composition and, post-preparation treatments (thermal treatments, electron irradiation etc.). Studies on electron irradiation induced changes in the structure of metallic glasses are reported [6,7], affecting their magnetic properties [7], via radiation-enhanced diffusion. However, reports on effect of electron irradiation on magnetic properties are rather limited [6,7]. Therefore in the present work, we report electron-irradiation induced changes in structural and magnetic properties of Co57.6Fe14.4Si4.8B19.2Nb4, Fe72Si4.8B19.2Nb4 and, Co72Si4.8B19.2Nb4 metallic glasses using magnetic hysteresis and, synchrotron X-ray diffraction measurements. 2. Experimental details Metallic glass Ribbons of nominal composition Co57.6Fe14.4Si4.8B19.2Nb4 (labelled as sample A), Fe72Si4.8B19.2Nb4, (labelled as sample B) and, Co72Si4.8B19.2Nb4 (labelled as sample C) were prepared by planar flow casting in air on a Cu wheel at Wigner Research Centre for Physics, Budapest (Hungary). Electron irradiation of the samples were done by using the electron irradiation facility available at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore (India). The specimens were surface treated at 700 keV electron beam energy and 1.5 mA beam current
http://dx.doi.org/10.1016/j.jallcom.2014.01.236 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: S.N. Kane et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.01.236
2
S.N. Kane et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx
using a DC accelerator. The sample was placed on the conveyor system in air. The electron beam obtained from the accelerator is scanned in scan horn with frequency of 100 Hz. This scanned beam is transmitted in air through 50 lm titanium foil. The sample to be irradiated was placed 100 mm below the titanium foil in air. The elliptical beam of dimension 100 mm 120 mm falls on the sample. The sample was moved with velocity of 20 m/min. in the beam path. Five different electron doses – 15, 45, 75, 105 and 150 kilo Gray (kGy) were given to as-cast samples. Hysteresis loops of 80 mm long samples were measured using the conventional induction technique at 50 Hz [8], using a compensated pick-up coil pair (each containing 3000 turns) for field flux compensation. Magnetic field was applied by a 200 long solenoid containing 1651 turns. Maximum field (Hmax) ±1 kA/m was used for hysteresis measurements. Raw data corresponding to measured hysteresis loops was obtained by a digital storage oscilloscope and, was analyzed using a MatlabÒ based program, to obtain coercivity (Hc) and, saturation induction (Bs). X-ray Diffraction (XRD) experiments were carried out by using angle dispersive X-ray Diffraction (ADXRD) beamline BL-12 at 21 keV (17 keV for sample A) using Mar 345 image plate at Indus 2 Synchrotron Radiation Source, RRCAT, Indore (India). XRD data was analyzed to obtain Radial Distribution Function (RDF) to get information on electron-irradiation induced structural changes in the studied samples. RDF provides information on the distribution of elements in various coordination shells.
a
1.0
B (Tesla)
0.5
As-cast 15 kGy 45 kGy 75 kGy 105 kGy 150 kGy
Co57.6 Fe14.4 Si4.8 B19.2 Nb4
Sample A
0.0
-0.5
-1.0 -60
Integration between the adjacent minima gives the average number of neighbouring atoms in a coordination shell. Also various maxima show the most probable position for the atoms in that coordination shell. Here the first coordination shell shows the TM–TM distance (TM–Transition Metal). The TM–TM distance and, the average number of atoms in the coordination shell for as quenched and electron irradiated samples was calculated.
3. Results and discussions Fig. 1(a)–(c) respectively depicts the electron irradiation dose dependence of hysteresis loops in sample A, B and C. Perusal of Fig. 1 depicts the effect of variation of electron irradiation in the studied samples and, it is worth noting that the studied samples (whose compositions are different) respond differently to their exposure to difference in the electron dose. Fig. 2 depicts the electron irradiation dependence of coercivity (measured within the accuracy of 0.5 A/m) in samples A, B and C. Perusal of Fig. 2 depicts that, variation of specimen composition and, electron dose shows changes in coercivity (Hc), although one can not deduce a very clear trend in view of the scattering of the points. In sample A, Hc oscillates along an average constant value. For sample B, not much variation of Hc is observed (except for the point corresponding to the sample irradiated with 120 kGy dose). Sample C displays an Hc reduction after an irradiation with 15 kGy dose and, for higher doses it exhibits practically a constant value. Observed changes in Hc values are ascribable to the appearance of more ordered phase in the specimens via electron irradiation.
25 -40
-20
0
20
40
60
Sample A
H (A/m)
Sample B
20
0.5
B (Tesla)
Sample C Fe 72 B19.2 Si4.8 Nb4
As-cast 15 kGy 45 kGy 75 kGy 105 kGy 150 kGy
Hc (A/m)
b
1.0
Sample B
15
10
0.0
5 -0.5
0
40
80
120
160
Dose (kGy) -1.0 -60
Fig. 2. Electron irradiation dose dependence of coercivity in the studied samples.
-40
-20
0
20
40
60
H (A/m) 1.0
B (Tesla)
0.5
0.0
As-cast 15 kGy 45 kGy 75 kGy 105 kGy 150 kGy
Sample B,
Sample C
Sample C 1.0
-0.5
-1.0 -60
Sample A,
1.2
Co72 B19.2 Si4.8 Nb4
Bs (Tesla)
c
0.8
0.6
-40
-20
0
20
40
60
H (A/m) Fig. 1. Electron irradiation dose dependence of hysteresis loops: (a) sample A, (b) sample B and (c) sample C.
0.4
0
40
80
120
160
Dose (kGy) Fig. 3. Electron irradiation dose dependence of saturation induction in the studied samples.
Please cite this article in press as: S.N. Kane et al., J. Alloys Comp. (2014), http://dx.doi.org/10.1016/j.jallcom.2014.01.236
3
a
10
Normalized Intensity
Intensity (Arb. Units)
S.N. Kane et al. / Journal of Alloys and Compounds xxx (2014) xxx–xxx
8
Sample C
Sample B Sample A 0
4
8
q = 4πsin (θ)/λ
12 (Α-1)
6 4 2 0
Fig. 4. Synchrotron XRD of the studied samples. Line/symbols are for electron irradiated/as cast samples.
2
4
6
8
10
12
q (1/Angstrom)
b
100 80
RDF
Fig. 3 shows the electron irradiation dependence of saturation induction in samples A, B and C. Perusal of Fig. 3 depicts a clear trend of Bs as a function of electron irradiation dose for the studied samples This behaviour can be understood in terms of the appearance of a more ordered phase with electron irradiation and, has strong dependence on specimen composition. Sample B (Fe-rich) exhibits increase of Bs with increase of electron irradiation dose, whereas sample C (Co-rich) displays decrease of Bs with increase of electron irradiation dose. Thus, Fe-rich (sample B) and Co-rich (sample C) samples show opposite behaviour of Bs with electron irradiation dose. But sample A which contains both Fe and Co shows intermediate behaviour, which can be seen very clearly in Fig. 3, ascribable to opposite effects of Fe and Co on Bs. It is interesting to note that in case of sample B, the Bs increase by 62% after electron irradiation with a dose of 15 kGy. Present results show that in Fe-based metallic glasses, a low electron irradiation dose (as low as 15 kGy) helps in increasing Bs, almost without any increase of Hc, whereas it works adversely for Co-based samples. Fig. 4 depicts the synchrotron XRD of the studied samples (line/ symbols are for electron irradiated/as cast samples). The structure of a monatomic amorphous sample in real space can be described by pair distribution function g(r), which is proportional to the probability of finding an atom at a position r relative to the reference atom taken at the origin. Radial Distribution Function (RDF), related to g(r) by the relation RDF = 4prq0g(r), has been calculated by Fourier transform of normalized and corrected X-ray scattering data. Since the technique is based on the Fourier transform, large q measurements are needed for a reasonable result. Therefore, we have done calculations for only sample B and sample C. The details of the calculations are given in [9]. We have done calculations in the frame work of monatomic sample; although our sample is polyatomic. This can be justified because the only major scatterers in our samples are Transition Metal (TM). Other scatterers are either low Z (Si and B) or very small in quantity (Nb). Therefore, we have done the calculations in the framework of monatomic sample. This is in agreement with a recent publication [10], where similar arguments were given. Corrected and normalized X-ray diffraction data (Fig. 5(a)) and RDF (Fig. 5(b)) are given for sample C. The fit parameters for the first coordination shell are shown in Table 1, for samples B and C (as quenched as well as electron irradiated). A closer look at Table 1 shows that TM–TM distance do not show appreciable changes and, almost remains the same (1.64 ± 0.1 Å) for sample B, whereas, it decreases for sample C; on electron irradiation. The width of the first coordination shell, however, decreases considerably for both the samples on electron irradiation. The decrees of width clearly indicate that the amorphous matrix is transforming to more ordered phase on electron irradiation, showing noticeable changes in Bs values and also a strong compositional dependence, especially for sample B and C, as can be seen in Fig. 3. More studies on various other samples
0
60 40 20 0 0
2
4
6
8
10
r (Angstrom) Fig. 5. (a) Corrected and normalized X-ray diffraction data and (b) RDF for sample C.
Table 1 TM–TM distance and the average number of atoms in the coordination shell for as quenched and electron irradiated samples. Sample details
TM–TM distance (Å)
Average number of atoms in the first coordination shell
Width of the first coordination shell
Sample C (as quenched) Sample C (electron irradiated) Sample B (as quenched) Sample B (electron irradiated)
2.62 2.59 2.65 2.63
11.39 12.61 12.92 13.61
1.07 0.55 1.1 0.52
and other treatments like thermal annealing need to be carried out to work out in order to establish a definitive correlation between structural and magnetic properties. To summarize, studied samples which have differences in composition, respond differently to electron irradiation. Results show that variation in composition show changes in coercivity. Low electron irradiation dose of 15 kGy enhances saturation magnetization up to 62% in specimen B. Synchrotron XRD measurements indicate that the amorphous matrix is transforming to more ordered phase on electron irradiation, ascribable to the observed changes in magnetic properties.
Acknowledgements This work is supported by Indo–Portuguese joint project No. Int/Portugal/P-07/2013. MS (Research fellowship recipient) is supported by UGC-DAE CSR, Indore project CSR-I/CRS51/2011-12]. AG
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