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Nanometric crystallization of amorphous ribbons by DC Joule heating
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 1417–1418
Nanometric crystallization of amorphous ribbons by DC Joule heating ! C. Moron*, F. Maganto, A. Garc!ıa ! Dpto. S.I.A., E.U. Informatica (U.P.M.), Ctra. Valencia Km. 7, 28031 Madrid, Spain
Abstract We report the results of studies on the development of nanocrystalline phase by DC Joule heating. Structural and magnetic properties, after various annealing conditions, are reported. We show that DC Joule heating is an effective technique for control of nanometric crystallization and it is also compared with respect to conventional heat treatment and laser annealing. In Fe73:5 Nb3 Cu1 Si13:5 B9 ; the average grain size of Joule heated samples is significantly lower than in the furnace and laser annealed alloy. r 2003 Elsevier B.V. All rights reserved. PACS: 75.50.K; 81.40.G; 61.43 Keywords: Nanocrystalline material; Crystallization amorphous material; Joule heating
In the last years, a great deal of effort has been made to obtain nanocrystalline ferromagnetic materials, since they have improved soft magnetic properties in comparison to similar composition materials with crystalline or amorphous structure [1]. Devitrified glassy Fe73:5 Nb3 Cu1 Si13:5 B9 ; which is obtained by heat treatment, is an example of these materials. Annealing is generally performed in a temperature-programmable furnace [2,3] or by laser annealing [4]. During the last decade, increasing attention has been devoted to the development of fast annealing techniques of amorphous metallic ribbons, in order to check the possibility of obtaining off-equilibrium crystallization products or phases characterised by novel properties. In particular, the techniques exploiting the Joule heat released by an electrical current flowing in the sample have become fashionable due to their intrinsic conceptual simplicity [5,6]. The so-called technique of DC Joule heating involves relatively low electrical currents (up to 4 A) flowing for long times (1–100 s) and emerges as the natural choice when the details of the structural transformations occurring within the sample have to be known with accuracy. *Corresponding author. Fax: +34-91-336-7915. ! E-mail address: [email protected] (C. Moron).
It should be explicitly noted that DC Joule heating in vacuum has some real advantages over similar methods. In fact, the changes in temperature (including those that occur during crystallization) may be accurately described by a rather simple model, whose validity has been tested on various alloy systems [7]. The interest of DC Joule heating in the present context is related to the fact that it provides nanocrystalline Fe73:5 Nb3 Cu1 Si13:5 B9 with distinctly improved physical properties. Joule-heated samples of this alloy turn out to be characterised by lower grain sizes (even at large crystalline fractions) and higher magnetic permeability values with respect to furnace-annealed ribbons of the same composition. In this work, we report the results of studies on the development of nanocrystalline phase by DC Joule heating. Structural and magnetic properties, after various annealing conditions, are reported. We show that DC Joule heating is an effective technique for control of nanometric crystallization and it is also compared with respect to conventional heat treatment and laser annealing. Melt-spun ribbon of amorphous alloy with composition Fe73:5 Nb3 Cu1 Si13:5 B9 (thickness 20 mm) was used for the studies. Structural changes with the treatments have been analysed by X-ray diffraction and by
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.145
ARTICLE IN PRESS 1418
! et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1417–1418 C. Moron
conventional transmission electron microscopy. The thermal treatments used with the samples were: (1) The technique of DC Joule heating in vacuum has been applied to submit samples of these amorphous metallic alloys to heating rates (210 C=s) sensibly higher than those usually achieved either in a conventional furnace. The sample is kept within a vacuum chamber and heated by a longitudinal intensity current. (2) The annealing performed in a furnace under argon atmosphere with heating rates close to 10 C=min and the annealing time was always 1 h: The crystallization processes were studied by differential scanning calorimeter and by differential thermoanalysis. (3) The laser annealing by means of a cw CO2 laser. Various laser treatments were performed by changing the incident laser power and the irradiation time. The technique of DC Joule heating in vacuum has been applied in a ribbon strip, length of the order of 0:1 m: The sample is kept within a vacuum chamber and heated by a current flowing along its major axis. By choosing suitable dimensions and shapes of the two pairs of current and voltage electrodes, and of the sample holder, it becomes possible to make the conduction losses negligible (at least for temperatures higher than 600 C and for times not exceeding 100 s; i.e. in the usual experimental conditions) with respect to the radiative losses, which are particularly enhanced in this case by the very high surface-to-volume ratio of the samples [7]. Fig. 1 shows the initial permeability mi of Joule-heated samples as a function of different electrical currents I for the same time ð3 sÞ: As can be seen in the figure, the nanocrystallization corresponds to the sharp peak centred at I ¼ 3:5 A: For higher currents, mi drops to vanishingly small values owing to boride phase development. After different thermal treatments, the structural characterization of the samples are shown in Table 1. The volume fraction V % of the crystalline phase was measured from the ratio of the crystalline peaks are to the amorphous ones. In this table, D is the average grain size, Tan the annealing temperature and tan the annealing time. The enhancement of mi is higher in Joule heated samples than in conventionally annealed ones. As can be seen in the table, this effect is most probably related, to some extent, to the finer grain size ð11 nmÞ observed through X-ray analysis in Joule heated nanocrystalline samples with respect to the one measured in furnaceannealed materials (14 nm for high crystalline fractions) and to the one measured in laser-annealed samples (15 nm for high crystalline fractions). DC Joule heating in vacuum is very effective in producing nanocrystalline Fe73:5 Nb3 Cu1 Si13:5 B9 with
Fig. 1. Behaviour of the initial magnetic permeability mi with different electrical currents in samples submitted to Joule heating during 3 s: Table 1 Thermal treatment data and X-ray results
D (nm) Tan ð CÞ tan (s) V (%)
Furnace
Laser
Joule heating
14 550 60 75
15 800 0.3 70
11 630 3 80
extremely high magnetic permeability. Rapid heating allows nanocrystallization to occur in a much shorter time than in conventional anneals. Also, the grain size observed is lower in Joule heated samples that the annealed samples with laser and furnace conventional. This work has been partially supported by the Spanish CICYT, by the C.E.E. under FEDER project No. UNPM00-33-018 and by the Universidad Polite! cnica de Madrid under project AM0107.
References [1] G. Herzer, J. Magn. Magn. Mater. 112 (1992) 258. [2] Y. Yoshizawa, S. Oguna, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. ! [3] L. Pascual, C. Gomez-Polo, P. Mar!ın, M. V!azquez, H.A. Davies, J. Magn. Magn. Mater. 203 (1999) 79. [4] L. Lanotte, V. Iannotti, J. Appl. Phys. 78 (1995) 3531. . [5] D. Holzer, P. Tiberto, A. Hernando, R. Grosinger, H. Sassik, E. Esteverz-Rams, J. Magn. Magn. Mater. 169 (1997) 303. [6] R. Houssa, V. Franco, A. Conde, J. Magn. Magn. Mater. 203 (1999) 199. [7] P. Allia, M. Baricco, P. Tiberto, F. Viani, Phys. Rev. B 47 (1993) 3118.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 1417–1418
Nanometric crystallization of amorphous ribbons by DC Joule heating ! C. Moron*, F. Maganto, A. Garc!ıa ! Dpto. S.I.A., E.U. Informatica (U.P.M.), Ctra. Valencia Km. 7, 28031 Madrid, Spain
Abstract We report the results of studies on the development of nanocrystalline phase by DC Joule heating. Structural and magnetic properties, after various annealing conditions, are reported. We show that DC Joule heating is an effective technique for control of nanometric crystallization and it is also compared with respect to conventional heat treatment and laser annealing. In Fe73:5 Nb3 Cu1 Si13:5 B9 ; the average grain size of Joule heated samples is significantly lower than in the furnace and laser annealed alloy. r 2003 Elsevier B.V. All rights reserved. PACS: 75.50.K; 81.40.G; 61.43 Keywords: Nanocrystalline material; Crystallization amorphous material; Joule heating
In the last years, a great deal of effort has been made to obtain nanocrystalline ferromagnetic materials, since they have improved soft magnetic properties in comparison to similar composition materials with crystalline or amorphous structure [1]. Devitrified glassy Fe73:5 Nb3 Cu1 Si13:5 B9 ; which is obtained by heat treatment, is an example of these materials. Annealing is generally performed in a temperature-programmable furnace [2,3] or by laser annealing [4]. During the last decade, increasing attention has been devoted to the development of fast annealing techniques of amorphous metallic ribbons, in order to check the possibility of obtaining off-equilibrium crystallization products or phases characterised by novel properties. In particular, the techniques exploiting the Joule heat released by an electrical current flowing in the sample have become fashionable due to their intrinsic conceptual simplicity [5,6]. The so-called technique of DC Joule heating involves relatively low electrical currents (up to 4 A) flowing for long times (1–100 s) and emerges as the natural choice when the details of the structural transformations occurring within the sample have to be known with accuracy. *Corresponding author. Fax: +34-91-336-7915. ! E-mail address: [email protected] (C. Moron).
It should be explicitly noted that DC Joule heating in vacuum has some real advantages over similar methods. In fact, the changes in temperature (including those that occur during crystallization) may be accurately described by a rather simple model, whose validity has been tested on various alloy systems [7]. The interest of DC Joule heating in the present context is related to the fact that it provides nanocrystalline Fe73:5 Nb3 Cu1 Si13:5 B9 with distinctly improved physical properties. Joule-heated samples of this alloy turn out to be characterised by lower grain sizes (even at large crystalline fractions) and higher magnetic permeability values with respect to furnace-annealed ribbons of the same composition. In this work, we report the results of studies on the development of nanocrystalline phase by DC Joule heating. Structural and magnetic properties, after various annealing conditions, are reported. We show that DC Joule heating is an effective technique for control of nanometric crystallization and it is also compared with respect to conventional heat treatment and laser annealing. Melt-spun ribbon of amorphous alloy with composition Fe73:5 Nb3 Cu1 Si13:5 B9 (thickness 20 mm) was used for the studies. Structural changes with the treatments have been analysed by X-ray diffraction and by
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.145
ARTICLE IN PRESS 1418
! et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1417–1418 C. Moron
conventional transmission electron microscopy. The thermal treatments used with the samples were: (1) The technique of DC Joule heating in vacuum has been applied to submit samples of these amorphous metallic alloys to heating rates (210 C=s) sensibly higher than those usually achieved either in a conventional furnace. The sample is kept within a vacuum chamber and heated by a longitudinal intensity current. (2) The annealing performed in a furnace under argon atmosphere with heating rates close to 10 C=min and the annealing time was always 1 h: The crystallization processes were studied by differential scanning calorimeter and by differential thermoanalysis. (3) The laser annealing by means of a cw CO2 laser. Various laser treatments were performed by changing the incident laser power and the irradiation time. The technique of DC Joule heating in vacuum has been applied in a ribbon strip, length of the order of 0:1 m: The sample is kept within a vacuum chamber and heated by a current flowing along its major axis. By choosing suitable dimensions and shapes of the two pairs of current and voltage electrodes, and of the sample holder, it becomes possible to make the conduction losses negligible (at least for temperatures higher than 600 C and for times not exceeding 100 s; i.e. in the usual experimental conditions) with respect to the radiative losses, which are particularly enhanced in this case by the very high surface-to-volume ratio of the samples [7]. Fig. 1 shows the initial permeability mi of Joule-heated samples as a function of different electrical currents I for the same time ð3 sÞ: As can be seen in the figure, the nanocrystallization corresponds to the sharp peak centred at I ¼ 3:5 A: For higher currents, mi drops to vanishingly small values owing to boride phase development. After different thermal treatments, the structural characterization of the samples are shown in Table 1. The volume fraction V % of the crystalline phase was measured from the ratio of the crystalline peaks are to the amorphous ones. In this table, D is the average grain size, Tan the annealing temperature and tan the annealing time. The enhancement of mi is higher in Joule heated samples than in conventionally annealed ones. As can be seen in the table, this effect is most probably related, to some extent, to the finer grain size ð11 nmÞ observed through X-ray analysis in Joule heated nanocrystalline samples with respect to the one measured in furnaceannealed materials (14 nm for high crystalline fractions) and to the one measured in laser-annealed samples (15 nm for high crystalline fractions). DC Joule heating in vacuum is very effective in producing nanocrystalline Fe73:5 Nb3 Cu1 Si13:5 B9 with
Fig. 1. Behaviour of the initial magnetic permeability mi with different electrical currents in samples submitted to Joule heating during 3 s: Table 1 Thermal treatment data and X-ray results
D (nm) Tan ð CÞ tan (s) V (%)
Furnace
Laser
Joule heating
14 550 60 75
15 800 0.3 70
11 630 3 80
extremely high magnetic permeability. Rapid heating allows nanocrystallization to occur in a much shorter time than in conventional anneals. Also, the grain size observed is lower in Joule heated samples that the annealed samples with laser and furnace conventional. This work has been partially supported by the Spanish CICYT, by the C.E.E. under FEDER project No. UNPM00-33-018 and by the Universidad Polite! cnica de Madrid under project AM0107.
References [1] G. Herzer, J. Magn. Magn. Mater. 112 (1992) 258. [2] Y. Yoshizawa, S. Oguna, K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. ! [3] L. Pascual, C. Gomez-Polo, P. Mar!ın, M. V!azquez, H.A. Davies, J. Magn. Magn. Mater. 203 (1999) 79. [4] L. Lanotte, V. Iannotti, J. Appl. Phys. 78 (1995) 3531. . [5] D. Holzer, P. Tiberto, A. Hernando, R. Grosinger, H. Sassik, E. Esteverz-Rams, J. Magn. Magn. Mater. 169 (1997) 303. [6] R. Houssa, V. Franco, A. Conde, J. Magn. Magn. Mater. 203 (1999) 199. [7] P. Allia, M. Baricco, P. Tiberto, F. Viani, Phys. Rev. B 47 (1993) 3118.