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Magnetic and calorimetric studies of amorphous Co74Fe4Mn4B12Si6
June 1995
ELSEVIER
Materials Letters 24 (1995) 139-142
Magnetic and calorimetric studies of amorphous Co,,Fe,Mn,B 1& H. Atnnani a,*, F. Delaunay a, J.M. Saiter b, R. Krishnan ‘, P. Vigier a aGroupe de Me?allurgie Physique (URA 808 CNRS), Faculte’ des Sciences, Universite’de Rouen, 76134 Mont Saint Aignan Cedex, France b L.aboratoire c!‘Etude et de Caractkrisation des PolymLres et a’es Amorphes, Faculte’des Sciences, Universite’de Rouen, 76134 Mont Saint Aignan Cedex, France ’ Laboratoire de Magnitisme, CNRS, 92195 Meudon Cedex, France
Received 10 January 1995; in final form 9 April 1995; accepted 9 April 1995
Abstract The magnetization and thermal stability of Co74Fe4MhB,2Si6 amorphous ribbons are studied. The Curie temperature determined from magnetization and differential scanning calorimetry measurements is Tc = 680 K. An activation energy of 3.84 eV, for the devitrification process, is determined from the Kissinger method. Our data, compared with those obtained by other authors on amorphous FeBX (X = Nd, Ho, Er), show that amorphous Co74Fe4Mn.,B,2Si,exhibits good thermal stability but not as good as metallic glasses doped with a rare earth metal.
1. Introduction Cobalt-based amorphous alloys are interesting in high-frequency applications. The addition of manganese to these alloys is very useful. Indeed, it was shown that Mn possesses a high moment of 3.5 ,.&B[ 1] and
that a very small amount of Mn leads to an increase of the magnetization of the alloy [ 21. On the other hand, a small amount of Mn shifts the devitrification process (characterized by the temperature T,) beyond the ferromagnetic to paramagnetic transition (characterized by the Curie temperature Tc) without decreasing the magnetization [ 31. For Co-Mn-B amorphous alloys, the effect of Mn on the magnetization depends on the B content. For instance, at 4.2 K, the manganese increases the magnetization at high B concentrations. Co-Fe-Mn-B-Si amorphous alloys are known to be ferromagnetic at roolm temperature, besides presenting * Corresponding author. 0167-577x/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO167-577x(95)00077-1
an interesting magnetostrictive’ property. By varying the Fe concentration, the magnetostriction parameter (h) changes continuously from negative to positive values [4]. Nevertheless, only a few investigations regarding the magnetic and devitrification behaviour of this last class of materials have been reported [ 5,6]. This work deals with the characterization of amorphous CoT4Fe4MQB12S&ribbons. New data concerning the magnetization, the devitrification processes and the thermal stability are reported.
2. Experimental Amorphous Co,,Fe,M&B,,Si, ribbons were prepared by the single roller melt spinning technique. The purity of the different elements was 99.99% for B, Mn, Si, and 99.999% for Fe and Co. The ribbons were 3 mm wide and 30 pm thick. The amorphous state of the samples was checked by X-ray diffraction. The com-
140
H. Atmani et al. /Materials
Letters 24 (1995) 139-142
position and the homogeneity were controlled by electron probe microanalysis. During the susceptibility measurements, performed on a Faraday balance magnetometer, the samples were heated from room temperature to 850 K with a heating rate of 8 K/min. The magnetization field varied within the range 0. l-l .O T. Calorimetric investigations were performed using a differential scanning calorimeter (DSC 7 Perkin-Elmer) under a constant flow of nitrogen, and with heating rates varying in the range 5-20 K/min. The calibrations of the calorimeter, in energy and temperature, were performed from the determina-
tion of the enthalpy and the temperature of fusion of indium. All calorimetric data were normalized to 1 mg.
3. Results In Fig. 1, the variation of the susceptibility with temperature for various magnetic fields is displayed. For H= 0.6 T, the transition from the ferromagnetic to the paramagnetic state is observed at 682 f 10 K. The same is true for the other magnetic fields. For a given temperature, the higher the magnetic field, the lower
0.4 -
.*
0.3 --
. a 0 * -: E’ 5
9..
.
. mgm....mmg
.
0.2 --
,x
0.1
--
0-I
I 250
350
450
550
450
750
a50
950
TO
Fig.l.Thel/~versusTcurvesfordifferentfields:(X)H=O.~T,(A)H=0.4T;(~)H=0.6T;(~)H=l.OT. P(mW) IL-.-._.
Fig.2.TheDSCcurvesobtaioedfordiffenzntheatingrates:
-._
(a) r=5K/min,(b)
r=lOK/min,
(c) r=HK/min,(d)
r=2OK/min.
H. Atmani et al. /Materials Letters 24 (1995) 139-142
Table 1 Variation of the devitrification temperature (TX) with the heating rate observed for the Cq,Fe,J&BlzSi, amorphous ribbon r (K/min)
X-ray diffraction. On increasing the heating rate, this peak is shifted towards higher temperatures. The devitrification temperatures TX given in Table 1 are those taken at the peak deflection.
Tx (K)
5 10 15 20
141
829 840 842 847
4. Discussion The magnetization is deduced from the susceptibility given by the following relationship:
the magnetic susceptibility. The DSC thermograms obtained, for different heating rates, on Co7.,Fe4Mn4Bi2Si6are shown in Fig. 2. On each curve, the first thermal reaction observed at around 670 K, as a deflection rather than an endothermic peak and exemplified in Fig. 2 for one of the alloys, is identified as the Curie transition. In addition, at higher temperatures, a sharp exothermic peak is observed. This reaction corresponds to the devitrification process, as confirmed by
x( l/H) =alH+,yo,
where u is the magnetization and x0 the paramagnetic susceptibility. So the values of acan be determined, at each temperature, from the slope of a plot of x against 1lH. This allows, when the same calculations are performed for each investigated temperature, the variations of (Twith the temperature to be known. The results obtained for Co74Fe4Mn,B1ZSisare reported in Fig. 3. The Curie temperature Tc = 678 K is determined by extrapolation of the curve a=f( 7) to o= 0. The value of Tc obtained here for Co,4Fe4Mn4B1& glass is consistent with those reported for other Co containing alloy glasses where Tc increases with Co concentration (see Table 2). The kinetics of the first-order crystallization process is usually described, for metallic glasses, by the following relationship:
Table 2 Curie temperatures (T,-) observed for different metallic glasses Tc (K)
Ref.
723 713 643 645 663 662
[71 [81 191 [81 [91 this work
(1)
dzldt=K(Z’)(l-z),
(2)
..-mmmmmm =. . . . l. ...
01
I 250
350
4s
550
6.9
750
Too
Pig.3.TherrvtrsusTcurve(aisobtainedforeachtemperature,fromtheslopeoffhecwex=f(l/H)).
850
950
142
H. Atmani et al. /Materials
Letters 24 (1995) 139-142
(and as aconsequence the thermal stability) is however low compared with those obtained for metallic glasses doped with a rare earth metal (for instance, 6.4 eV per atom for Feso,3Ho,.,B,, [ 111 and 5.91 eV per atom for Fe77Nd3B20[ 12]), or for Fe-based glasses doped with Si (for instance, 5.3 eV per atom for Fe&04B1sSi3 [ 51) . Nevertheless, the opposite behaviour is observed when the comparison is made with non-doped Fe-based glasses; for instance an apparent activation energy of 2 eV per atom was obtained for the Fes0B20glass [ 131. -16.5
I
I
I
1
I
,
11.80
11.85
11.90
11.95
12.00
12.05
1OOOOLfx
Fig. 4. The ln(r/TZ) Kissinger method.
12.10
versus l/T. curve obtained following the
where dzldt is the rate of reaction, z the crystallized fraction, t the time, Tthe temperature, and K is assumed to follow an Arrhenius behaviour: K(T) = K. exp( - E,IkT) ,
(3)
E, being the apparent activation energy and K. a preexponential factor. Assuming that the rate of reaction is a maximum at the extremum of the peak (d*z/ dt* = 0),one obtains K. exp( - EJkT,)
= E,rfkTz
,
References
(K .‘)
(4)
where r is the heating rate, and this allows the apparent activation energy to be determined from the Kissinger plot (ln(rlTz) versus l/T,. Using data from Table 1, the Kissinger plot (Fig. 4) provides a value of 3.84 eV per atom for the apparent activation energy. Such a high value agrees with those generally observed for this class of materials [lo], attesting to the good thermal stability of the amorphous state for this system. This apparent activation energy
[ 11 R. Krishnan, K. Le Dang, P. Veillet and V.R.V. Ramanan, J. Appl. Phys. 57 (1985) 1394. [2] R. Krishnan, K. Le Dang and P. Veillet, J. Appl. Phys. 63 (1988) 2992. [3] Y. Obi, H. Morita and H. Fujimori, lEEE Trans. Magn. 16 (1981) 1132. [4] V. Madurga, M. Vasquez, A. Hemando and O.V. Nelson, Sol. Stat. Commun. 52 (1984) 701. [5] M. Millan, J. Leal and A. Conde, Proceedings of the Third International Workshop on Non-Crystalline Solids, P169, Spain, November 1991. [6] C.F. Conde and A. Conde, Proceedings of the Third International Workshop on Non-Crystalline Solids, p261, Spain, November 1991. [ 7 ] M. Tejedor, A. Femandez, M.J. Perez and V. Madurga, Phys. Stat. Sol. 135a (1993) 283. [ 81 M. Knobel, R. Sato Turtelli and R. Grossinger, J. Magn. Magn. Mater. 116 (1992) 154. [9] M. Sartorelli, F.P. Missell and R. Sato Turtelli, J. Magn. Magn. Mater. 88 (1990) 18. [ lo] P. Hansen, Handbook of magnetic materials, Vol. 6, ed. K.H.J. Buschow (Elsevier, Amsterdam, 1991) p. 335. [ 1l] G. Ravach, J.M. Saiter, A. Fnidiki and J. Teillet, Mater. Letters 18 (1993) 35. [ 121 M.T. Clavaguera-Mom, S. Surinach and V. Clavaguera, J. Mater. Res. 5 (1990) 1201. [ 131 F.L. Cumbrera, H. Miranda, A. Conde, R. Marquez and P. Vigier, J. Mater. Sci. 17 (1982) 2677.
ELSEVIER
Materials Letters 24 (1995) 139-142
Magnetic and calorimetric studies of amorphous Co,,Fe,Mn,B 1& H. Atnnani a,*, F. Delaunay a, J.M. Saiter b, R. Krishnan ‘, P. Vigier a aGroupe de Me?allurgie Physique (URA 808 CNRS), Faculte’ des Sciences, Universite’de Rouen, 76134 Mont Saint Aignan Cedex, France b L.aboratoire c!‘Etude et de Caractkrisation des PolymLres et a’es Amorphes, Faculte’des Sciences, Universite’de Rouen, 76134 Mont Saint Aignan Cedex, France ’ Laboratoire de Magnitisme, CNRS, 92195 Meudon Cedex, France
Received 10 January 1995; in final form 9 April 1995; accepted 9 April 1995
Abstract The magnetization and thermal stability of Co74Fe4MhB,2Si6 amorphous ribbons are studied. The Curie temperature determined from magnetization and differential scanning calorimetry measurements is Tc = 680 K. An activation energy of 3.84 eV, for the devitrification process, is determined from the Kissinger method. Our data, compared with those obtained by other authors on amorphous FeBX (X = Nd, Ho, Er), show that amorphous Co74Fe4Mn.,B,2Si,exhibits good thermal stability but not as good as metallic glasses doped with a rare earth metal.
1. Introduction Cobalt-based amorphous alloys are interesting in high-frequency applications. The addition of manganese to these alloys is very useful. Indeed, it was shown that Mn possesses a high moment of 3.5 ,.&B[ 1] and
that a very small amount of Mn leads to an increase of the magnetization of the alloy [ 21. On the other hand, a small amount of Mn shifts the devitrification process (characterized by the temperature T,) beyond the ferromagnetic to paramagnetic transition (characterized by the Curie temperature Tc) without decreasing the magnetization [ 31. For Co-Mn-B amorphous alloys, the effect of Mn on the magnetization depends on the B content. For instance, at 4.2 K, the manganese increases the magnetization at high B concentrations. Co-Fe-Mn-B-Si amorphous alloys are known to be ferromagnetic at roolm temperature, besides presenting * Corresponding author. 0167-577x/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO167-577x(95)00077-1
an interesting magnetostrictive’ property. By varying the Fe concentration, the magnetostriction parameter (h) changes continuously from negative to positive values [4]. Nevertheless, only a few investigations regarding the magnetic and devitrification behaviour of this last class of materials have been reported [ 5,6]. This work deals with the characterization of amorphous CoT4Fe4MQB12S&ribbons. New data concerning the magnetization, the devitrification processes and the thermal stability are reported.
2. Experimental Amorphous Co,,Fe,M&B,,Si, ribbons were prepared by the single roller melt spinning technique. The purity of the different elements was 99.99% for B, Mn, Si, and 99.999% for Fe and Co. The ribbons were 3 mm wide and 30 pm thick. The amorphous state of the samples was checked by X-ray diffraction. The com-
140
H. Atmani et al. /Materials
Letters 24 (1995) 139-142
position and the homogeneity were controlled by electron probe microanalysis. During the susceptibility measurements, performed on a Faraday balance magnetometer, the samples were heated from room temperature to 850 K with a heating rate of 8 K/min. The magnetization field varied within the range 0. l-l .O T. Calorimetric investigations were performed using a differential scanning calorimeter (DSC 7 Perkin-Elmer) under a constant flow of nitrogen, and with heating rates varying in the range 5-20 K/min. The calibrations of the calorimeter, in energy and temperature, were performed from the determina-
tion of the enthalpy and the temperature of fusion of indium. All calorimetric data were normalized to 1 mg.
3. Results In Fig. 1, the variation of the susceptibility with temperature for various magnetic fields is displayed. For H= 0.6 T, the transition from the ferromagnetic to the paramagnetic state is observed at 682 f 10 K. The same is true for the other magnetic fields. For a given temperature, the higher the magnetic field, the lower
0.4 -
.*
0.3 --
. a 0 * -: E’ 5
9..
.
. mgm....mmg
.
0.2 --
,x
0.1
--
0-I
I 250
350
450
550
450
750
a50
950
TO
Fig.l.Thel/~versusTcurvesfordifferentfields:(X)H=O.~T,(A)H=0.4T;(~)H=0.6T;(~)H=l.OT. P(mW) IL-.-._.
Fig.2.TheDSCcurvesobtaioedfordiffenzntheatingrates:
-._
(a) r=5K/min,(b)
r=lOK/min,
(c) r=HK/min,(d)
r=2OK/min.
H. Atmani et al. /Materials Letters 24 (1995) 139-142
Table 1 Variation of the devitrification temperature (TX) with the heating rate observed for the Cq,Fe,J&BlzSi, amorphous ribbon r (K/min)
X-ray diffraction. On increasing the heating rate, this peak is shifted towards higher temperatures. The devitrification temperatures TX given in Table 1 are those taken at the peak deflection.
Tx (K)
5 10 15 20
141
829 840 842 847
4. Discussion The magnetization is deduced from the susceptibility given by the following relationship:
the magnetic susceptibility. The DSC thermograms obtained, for different heating rates, on Co7.,Fe4Mn4Bi2Si6are shown in Fig. 2. On each curve, the first thermal reaction observed at around 670 K, as a deflection rather than an endothermic peak and exemplified in Fig. 2 for one of the alloys, is identified as the Curie transition. In addition, at higher temperatures, a sharp exothermic peak is observed. This reaction corresponds to the devitrification process, as confirmed by
x( l/H) =alH+,yo,
where u is the magnetization and x0 the paramagnetic susceptibility. So the values of acan be determined, at each temperature, from the slope of a plot of x against 1lH. This allows, when the same calculations are performed for each investigated temperature, the variations of (Twith the temperature to be known. The results obtained for Co74Fe4Mn,B1ZSisare reported in Fig. 3. The Curie temperature Tc = 678 K is determined by extrapolation of the curve a=f( 7) to o= 0. The value of Tc obtained here for Co,4Fe4Mn4B1& glass is consistent with those reported for other Co containing alloy glasses where Tc increases with Co concentration (see Table 2). The kinetics of the first-order crystallization process is usually described, for metallic glasses, by the following relationship:
Table 2 Curie temperatures (T,-) observed for different metallic glasses Tc (K)
Ref.
723 713 643 645 663 662
[71 [81 191 [81 [91 this work
(1)
dzldt=K(Z’)(l-z),
(2)
..-mmmmmm =. . . . l. ...
01
I 250
350
4s
550
6.9
750
Too
Pig.3.TherrvtrsusTcurve(aisobtainedforeachtemperature,fromtheslopeoffhecwex=f(l/H)).
850
950
142
H. Atmani et al. /Materials
Letters 24 (1995) 139-142
(and as aconsequence the thermal stability) is however low compared with those obtained for metallic glasses doped with a rare earth metal (for instance, 6.4 eV per atom for Feso,3Ho,.,B,, [ 111 and 5.91 eV per atom for Fe77Nd3B20[ 12]), or for Fe-based glasses doped with Si (for instance, 5.3 eV per atom for Fe&04B1sSi3 [ 51) . Nevertheless, the opposite behaviour is observed when the comparison is made with non-doped Fe-based glasses; for instance an apparent activation energy of 2 eV per atom was obtained for the Fes0B20glass [ 131. -16.5
I
I
I
1
I
,
11.80
11.85
11.90
11.95
12.00
12.05
1OOOOLfx
Fig. 4. The ln(r/TZ) Kissinger method.
12.10
versus l/T. curve obtained following the
where dzldt is the rate of reaction, z the crystallized fraction, t the time, Tthe temperature, and K is assumed to follow an Arrhenius behaviour: K(T) = K. exp( - E,IkT) ,
(3)
E, being the apparent activation energy and K. a preexponential factor. Assuming that the rate of reaction is a maximum at the extremum of the peak (d*z/ dt* = 0),one obtains K. exp( - EJkT,)
= E,rfkTz
,
References
(K .‘)
(4)
where r is the heating rate, and this allows the apparent activation energy to be determined from the Kissinger plot (ln(rlTz) versus l/T,. Using data from Table 1, the Kissinger plot (Fig. 4) provides a value of 3.84 eV per atom for the apparent activation energy. Such a high value agrees with those generally observed for this class of materials [lo], attesting to the good thermal stability of the amorphous state for this system. This apparent activation energy
[ 11 R. Krishnan, K. Le Dang, P. Veillet and V.R.V. Ramanan, J. Appl. Phys. 57 (1985) 1394. [2] R. Krishnan, K. Le Dang and P. Veillet, J. Appl. Phys. 63 (1988) 2992. [3] Y. Obi, H. Morita and H. Fujimori, lEEE Trans. Magn. 16 (1981) 1132. [4] V. Madurga, M. Vasquez, A. Hemando and O.V. Nelson, Sol. Stat. Commun. 52 (1984) 701. [5] M. Millan, J. Leal and A. Conde, Proceedings of the Third International Workshop on Non-Crystalline Solids, P169, Spain, November 1991. [6] C.F. Conde and A. Conde, Proceedings of the Third International Workshop on Non-Crystalline Solids, p261, Spain, November 1991. [ 7 ] M. Tejedor, A. Femandez, M.J. Perez and V. Madurga, Phys. Stat. Sol. 135a (1993) 283. [ 81 M. Knobel, R. Sato Turtelli and R. Grossinger, J. Magn. Magn. Mater. 116 (1992) 154. [9] M. Sartorelli, F.P. Missell and R. Sato Turtelli, J. Magn. Magn. Mater. 88 (1990) 18. [ lo] P. Hansen, Handbook of magnetic materials, Vol. 6, ed. K.H.J. Buschow (Elsevier, Amsterdam, 1991) p. 335. [ 1l] G. Ravach, J.M. Saiter, A. Fnidiki and J. Teillet, Mater. Letters 18 (1993) 35. [ 121 M.T. Clavaguera-Mom, S. Surinach and V. Clavaguera, J. Mater. Res. 5 (1990) 1201. [ 131 F.L. Cumbrera, H. Miranda, A. Conde, R. Marquez and P. Vigier, J. Mater. Sci. 17 (1982) 2677.