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Mössbauer and magnetic studies of amorphous and nanocrystalline Fe85.4Zr6.8−xNbxB6.8Cu1 (x=0, 1, 2) alloys
Journal of Magnetism and Magnetic Materials 215}216 (2000) 419}421
MoK ssbauer and magnetic studies of amorphous and nanocrystalline Fe Zr Nb B Cu (x"0, 1, 2) alloys \V V J. Zbroszczyk *, H. Fukunaga, J. Olszewski , W.H. CiurzynH ska , M. Hasiak , A. B"achowicz Institute of Physics, Technical University of Cze9 stochowa, Al. Armii Krajowej 19, 42-200 Cze9 stochowa, Poland Faculty of Engineering, Nagasaki University, Nagasaki, Japan
Abstract It was stated that the addition of Nb to the Fe Zr B Cu alloy leads to the decrease of the average hyper"ne "eld at Fe nuclei and Curie temperature of the amorphous materials. Moreover, the amount of the a-Fe phase in the nanocrystalline samples increases with the niobium content. The nanocrystalline alloy containing 2 at% Nb exhibits the highest initial magnetic susceptibility. 2000 Elsevier Science B.V. All rights reserved. Keywords: Nanocrystalline alloys; MoK ssbauer e!ect; Magnetic properties
Excellent soft magnetic properties can be found in nanocrystalline materials obtained by the controlled crystallization of Fe}B}Si amorphous ribbons containing 1% Cu and 3% Nb [1]. In this paper we investigate the e!ect of Nb addition on the microstructure and magnetic properties of Fe}Zr}B}Cu alloys. The amorphous Fe Zr B Cu Nb (x"0, \V V 1 or 2) alloys in the form of ribbons were produced by a rapid quenching method under a controlled argon atmosphere. The thickness and width of the ribbons were 15 lm and 3 mm, respectively. The amorphicity of the as-quenched ribbons was checked by X-ray di!raction and MoK ssbauer spectroscopy. From X-ray investigations the crystalline phase in the partially crystallized samples was also identi"ed. Moreover, from MoK ssbauer spectra analysis, the distribution of the magnetization in the samples, their phase composition and hyper"ne "eld at Fe nuclei in the phases were determined. The magnetic properties, i.e. the magnetic susceptibility and its disaccommodation were measured for toroidal samples of 2 cm inner diameter using a completely automated setup. The amplitude and frequency of the magnetizing "eld
* Corresponding author. Tel./fax: #48-34-3250-795. E-mail address: [email protected] (J. Zbroszczyk).
were 0.16 A/m and 2 kHz, respectively. All investigations were carried out for the samples in the as-quenched state and after annealing at 784 K for 5 s, 1, 10, 30 or 60 min. Moreover, from the measurements of the saturation magnetization versus temperature (using a force magnetometer), the Curie temperature for the amorphous alloys was determined. The transmission MoK ssbauer spectra of the as-quenched Fe Zr B Cu Nb (x"0, 1 or 2) alloys \V V consist of the broad, overlapped lines typical for amorphous systems. The spectra of the nanocrystalline alloys exhibit a complex hyper"ne structure and consist of at least two components (one ascribed to the a-Fe phase and the other to the residual amorphous matrix). The representative spectra for the amorphous and nanocrystalline samples of these alloys are shown in Fig. 1. Some results obtained from MoK ssbauer spectra analysis are presented in Table 1. It is seen that the average hyper"ne "eld for the amorphous alloys decreases with the Nb content. Moreover, the amount of the crystalline a-Fe phase in the nanocrystalline alloys, obtained by the same heat treatment, increases with the Nb concentration. One can notice (Table 1) that the sample of the Fe Zr B Cu alloy after annealing at 784 K for 5 s, 1 and 10 min reveals the large component of the magnetization perpendicular to the ribbon surface. A similar e!ect is observed in the Fe Zr B Cu Nb and
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 1 7 6 - 1
420
J. Zbroszczyk et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 419}421
Fig. 2. The hyper"ne "eld distributions for the Fe Zr B Cu Nb alloy in the as-quenched state (*) and annealed at 784 K for 1 min, after the extraction of the crystalline component (- - -). Fig. 1. The MoK ssbauer spectra of the nanocrystalline Fe Zr B Cu Nb alloy (a) in the as-quenched state, (b) after annealing at 784 K for 1 min: a-Fe phase (* ), interface (- - -), amorphous matrix (2).
Fe Zr B Cu Nb alloys after annealing at 784 K for 1 min. In the hyper"ne "eld distribution of the amorphous matrix (Fig. 2), one can distinguish the additional component as compared to the as-quenched state. That component may be ascribed to the interface zone [2] which comprises Fe atoms situated in crystal grain boundaries as well as those being in close contact with the "ne grains.
Thus, the thickness of the interfacial layer may be equal to at least two atomic distance (about 0.6 nm). Assuming spherical crystalline grains, we have found that the ratio of the thickness of the interface zone (t) to the grain diameter (D) is equal to about 0.13 for all investigated alloys annealed at 784 K for 5 s. However, this ratio decreases with the Nb content and annealing time. Moreover, it was found that the replacement of Zr atoms by Nb atoms in the amorphous Fe Zr B Cu alloy leads to the decrease of the Curie temperature (from 420 K for Fe Zr B Cu to 400 and 375 K for the Fe Zr B Cu Nb and Fe Zr B Cu Nb alloys, respectively).
Table 1 The intensity of the second line (A ) in Zeeman sextets, volume fraction of the a-Fe phase (< ) and the interface zone (< ), hyper"ne "eld of the crystalline a-Fe phase (B ) and the average hyper"ne "eld of the amorphous matrix and interface layer ((B ) and (B ) , respectively) for the Fe Zr B Cu Nb alloys \V V Nb content
Treatment at 784 K
A
x"0
As-q 5s 1 min 10 min As-q 5s 1 min 10 min As-q 5s 1 min 10 min
2.8 1.5 1.0 1.7 2.8 2.0 1.6 2.0 2.3 2.0 1.4 2.1
x"1
x"2
$0.1
V
B (T) $0.1
V
0.17 0.28 0.32
32.7 32.9 32.9
0.17 0.23 0.25
26.7 26.6 26.5
0.19 0.32 0.33
32.7 32.9 32.8
0.18 0.19 0.22
26.0 27.3 27.3
0.24 0.33 0.35
32.8 32.9 32.8
0.24 0.20 0.20
27.0 26.6 26.6
(B ) (T) $0.1
(B ) (T) $ 0.1 12.3 14.6 14.7 14.1 11.6 13.4 13.6 12.9 10.4 13.1 12.7 12.0
J. Zbroszczyk et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 419}421 Table 2 The magnetic susceptibility (v ) measured at room temperature of the Fe Zr B Cu Nb alloys in the as-quenched state \V V and after annealing at 784 K for 5 s and 1 min Nb content (at%)
x"0 x"1 x"2
v As-quenched
784 K/5 s
784 K/1 min
837 831 790
2089 2458 2724
3383 3500 4099
The microstructure of the investigated alloys in#uences their soft magnetic properties. The magnetic susceptibility of these alloys in the as-quenched state and after annealing at 784 K for 5 s and 1 min are presented in Table 2. One can notice that the highest value of the susceptibility is observed for the nanocrystalline Fe Zr B Cu Nb alloy. The niobium content in #uences also the intensity of disaccommodation in the
421
investigated alloys. The lowest maximum of the disaccommodation (*(1/s)"112;10\) occurring at about 0.5 A/m was observed for the Fe Zr B Cu Nb alloy in the as-quenched state. A similar behaviour was exhibited by the samples annealed at 784 K for 10, 30 and 60 min.
Acknowledgements This work was "nancially supported by the Polish Committee for Scienti"c Research (Grant No. 7 T082 022 17).
References [1] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [2] M. Miglierini, J.M. Greneche, J. Phys.: Condens. Matter 9 (1997) 2303.
MoK ssbauer and magnetic studies of amorphous and nanocrystalline Fe Zr Nb B Cu (x"0, 1, 2) alloys \V V J. Zbroszczyk *, H. Fukunaga, J. Olszewski , W.H. CiurzynH ska , M. Hasiak , A. B"achowicz Institute of Physics, Technical University of Cze9 stochowa, Al. Armii Krajowej 19, 42-200 Cze9 stochowa, Poland Faculty of Engineering, Nagasaki University, Nagasaki, Japan
Abstract It was stated that the addition of Nb to the Fe Zr B Cu alloy leads to the decrease of the average hyper"ne "eld at Fe nuclei and Curie temperature of the amorphous materials. Moreover, the amount of the a-Fe phase in the nanocrystalline samples increases with the niobium content. The nanocrystalline alloy containing 2 at% Nb exhibits the highest initial magnetic susceptibility. 2000 Elsevier Science B.V. All rights reserved. Keywords: Nanocrystalline alloys; MoK ssbauer e!ect; Magnetic properties
Excellent soft magnetic properties can be found in nanocrystalline materials obtained by the controlled crystallization of Fe}B}Si amorphous ribbons containing 1% Cu and 3% Nb [1]. In this paper we investigate the e!ect of Nb addition on the microstructure and magnetic properties of Fe}Zr}B}Cu alloys. The amorphous Fe Zr B Cu Nb (x"0, \V V 1 or 2) alloys in the form of ribbons were produced by a rapid quenching method under a controlled argon atmosphere. The thickness and width of the ribbons were 15 lm and 3 mm, respectively. The amorphicity of the as-quenched ribbons was checked by X-ray di!raction and MoK ssbauer spectroscopy. From X-ray investigations the crystalline phase in the partially crystallized samples was also identi"ed. Moreover, from MoK ssbauer spectra analysis, the distribution of the magnetization in the samples, their phase composition and hyper"ne "eld at Fe nuclei in the phases were determined. The magnetic properties, i.e. the magnetic susceptibility and its disaccommodation were measured for toroidal samples of 2 cm inner diameter using a completely automated setup. The amplitude and frequency of the magnetizing "eld
* Corresponding author. Tel./fax: #48-34-3250-795. E-mail address: [email protected] (J. Zbroszczyk).
were 0.16 A/m and 2 kHz, respectively. All investigations were carried out for the samples in the as-quenched state and after annealing at 784 K for 5 s, 1, 10, 30 or 60 min. Moreover, from the measurements of the saturation magnetization versus temperature (using a force magnetometer), the Curie temperature for the amorphous alloys was determined. The transmission MoK ssbauer spectra of the as-quenched Fe Zr B Cu Nb (x"0, 1 or 2) alloys \V V consist of the broad, overlapped lines typical for amorphous systems. The spectra of the nanocrystalline alloys exhibit a complex hyper"ne structure and consist of at least two components (one ascribed to the a-Fe phase and the other to the residual amorphous matrix). The representative spectra for the amorphous and nanocrystalline samples of these alloys are shown in Fig. 1. Some results obtained from MoK ssbauer spectra analysis are presented in Table 1. It is seen that the average hyper"ne "eld for the amorphous alloys decreases with the Nb content. Moreover, the amount of the crystalline a-Fe phase in the nanocrystalline alloys, obtained by the same heat treatment, increases with the Nb concentration. One can notice (Table 1) that the sample of the Fe Zr B Cu alloy after annealing at 784 K for 5 s, 1 and 10 min reveals the large component of the magnetization perpendicular to the ribbon surface. A similar e!ect is observed in the Fe Zr B Cu Nb and
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 1 7 6 - 1
420
J. Zbroszczyk et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 419}421
Fig. 2. The hyper"ne "eld distributions for the Fe Zr B Cu Nb alloy in the as-quenched state (*) and annealed at 784 K for 1 min, after the extraction of the crystalline component (- - -). Fig. 1. The MoK ssbauer spectra of the nanocrystalline Fe Zr B Cu Nb alloy (a) in the as-quenched state, (b) after annealing at 784 K for 1 min: a-Fe phase (* ), interface (- - -), amorphous matrix (2).
Fe Zr B Cu Nb alloys after annealing at 784 K for 1 min. In the hyper"ne "eld distribution of the amorphous matrix (Fig. 2), one can distinguish the additional component as compared to the as-quenched state. That component may be ascribed to the interface zone [2] which comprises Fe atoms situated in crystal grain boundaries as well as those being in close contact with the "ne grains.
Thus, the thickness of the interfacial layer may be equal to at least two atomic distance (about 0.6 nm). Assuming spherical crystalline grains, we have found that the ratio of the thickness of the interface zone (t) to the grain diameter (D) is equal to about 0.13 for all investigated alloys annealed at 784 K for 5 s. However, this ratio decreases with the Nb content and annealing time. Moreover, it was found that the replacement of Zr atoms by Nb atoms in the amorphous Fe Zr B Cu alloy leads to the decrease of the Curie temperature (from 420 K for Fe Zr B Cu to 400 and 375 K for the Fe Zr B Cu Nb and Fe Zr B Cu Nb alloys, respectively).
Table 1 The intensity of the second line (A ) in Zeeman sextets, volume fraction of the a-Fe phase (< ) and the interface zone (< ), hyper"ne "eld of the crystalline a-Fe phase (B ) and the average hyper"ne "eld of the amorphous matrix and interface layer ((B ) and (B ) , respectively) for the Fe Zr B Cu Nb alloys \V V Nb content
Treatment at 784 K
A
x"0
As-q 5s 1 min 10 min As-q 5s 1 min 10 min As-q 5s 1 min 10 min
2.8 1.5 1.0 1.7 2.8 2.0 1.6 2.0 2.3 2.0 1.4 2.1
x"1
x"2
$0.1
V
B (T) $0.1
V
0.17 0.28 0.32
32.7 32.9 32.9
0.17 0.23 0.25
26.7 26.6 26.5
0.19 0.32 0.33
32.7 32.9 32.8
0.18 0.19 0.22
26.0 27.3 27.3
0.24 0.33 0.35
32.8 32.9 32.8
0.24 0.20 0.20
27.0 26.6 26.6
(B ) (T) $0.1
(B ) (T) $ 0.1 12.3 14.6 14.7 14.1 11.6 13.4 13.6 12.9 10.4 13.1 12.7 12.0
J. Zbroszczyk et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 419}421 Table 2 The magnetic susceptibility (v ) measured at room temperature of the Fe Zr B Cu Nb alloys in the as-quenched state \V V and after annealing at 784 K for 5 s and 1 min Nb content (at%)
x"0 x"1 x"2
v As-quenched
784 K/5 s
784 K/1 min
837 831 790
2089 2458 2724
3383 3500 4099
The microstructure of the investigated alloys in#uences their soft magnetic properties. The magnetic susceptibility of these alloys in the as-quenched state and after annealing at 784 K for 5 s and 1 min are presented in Table 2. One can notice that the highest value of the susceptibility is observed for the nanocrystalline Fe Zr B Cu Nb alloy. The niobium content in #uences also the intensity of disaccommodation in the
421
investigated alloys. The lowest maximum of the disaccommodation (*(1/s)"112;10\) occurring at about 0.5 A/m was observed for the Fe Zr B Cu Nb alloy in the as-quenched state. A similar behaviour was exhibited by the samples annealed at 784 K for 10, 30 and 60 min.
Acknowledgements This work was "nancially supported by the Polish Committee for Scienti"c Research (Grant No. 7 T082 022 17).
References [1] Y. Yoshizawa, S. Oguma, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [2] M. Miglierini, J.M. Greneche, J. Phys.: Condens. Matter 9 (1997) 2303.