- Email: [email protected]
Mössbauer study of the in-plane anisotropy in annealed amorphous Fe81B13.5Si3.5C2 ribbons
Journal of Magnetism and Magnetic North-Holland, Amsterdam
MiiSSBAUER Fe,, B &3i
Materials
STUDY
229
53 (1985) 229-232
OF THE
IN-PLANE
ANISOTROPY
IN ANNEALED
AMORPHOUS
3,5Cz RIBBONS
T. METHASIRI Physics Department,
Chulalongkorn
University, Bungkok
10500, Thailund
J.R. CULLEN Naval Surface
Weapon Center, White Oak, Silver Spring, MD 20910, USA
and I.M. TANG Physics Department, Received
Mahidol
University, Bangkok
10400, Thailand
10 April 1985; in revised form 26 July 1985
MGssbauer spectra of amorphous Fe,,B,,,, Si 3 s C z ribbons (METGLAS 2605 SC) annealed in transverse magnetic field at 594 and 654 K were recorded for various orientations of the ribbons. It is determined that the in-plane projection of the anisotropy is 17’ off the transverse axis for the 594 K annealed specimen and 10” off the transverse axis for the 654 K specimen.
Much interest has recently been shown in the quaternary amorphous alloy Fe,, B,,,,Si 3,5C, (METGLAS * 2605 SC). Modzelewski et al. [l] have measured the magnetomechanical coupling and permeability of this and other amorphous ribbons which were annealed in a magnetic field applied in the plane of the ribbon and transverse to the long axis. Saegusa and Morrish have carried out a series of Massbauer measurements on the 2605 SC ribbons in order to characterise [2] the amorphous Fe,, B,,,,Si,., Cz alloys and to understand [3] the amorphous to crystalline transformation in this alloy. Bhatnager et al. [4] have also performed Mtissbauer measurements on this amorphous alloy. Saegusa and Morrish reported that there exists a magnetic anisotropy pointing out of the plane of the ribbon. The angle at which the anisotropy points out of the plane depends on the heat treatment of the ribbon after it is casted. Saegusa and * METGLAS Corp.
is a registered
trademark
of the Allied Chemical
0304-8853/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
Morrish [5] found the magnetic moment to be pointing at an average angle of 20” from the ribbon plane when the annealing temperature TA was less than 620 K. When TA was increased from 620 to 685 K, the average angle increased slowly to about 55”. An abrupt decrease to an apparent angle of 35” was observed as TA was increased from 685 to 690 K at which crystallization started to occur. The angle is an apparent one since the magnetic moments are randomly oriented once crystallization sets in. The formation of the anisotropy pointing out of the plane of the ribbon can be accounted for by the model used by Ok and Morrish [6] to explain the out-of-plane anisotropy of the magnetization in the amorphous Fe,,B,,Si, alloy (METGLAS 2605 C). The differences in the directions of the anisotropy in the 2605 SC ribbons for TA below 620 K and for TA between 620 and 685 K are probably due to the differences in the compressive stress in the ribbon caused by the differing atomic rearrangements which are occurring in the two annealing regions [41. B.V.
230
T. Merhasirr
et al. / In -plane
misotrop_); in (1-Fe,,
The purpose of this note is to report our measurements of the Mossbauer effect in a field annealed Fe,, B,,,,Si 3,5C, ribbon which indicate a difference in the direction of the projection of the magnetic moment in the plane of the ribbon when the ribbons are annealed in a transverse field (> 2 kOe) at 594 and 654 K for 20 min durations. A standard Mossbauer spectrometer using 57Co in Pd as source was used to obtain the six peak patterns expected of the hyperfine split 14.4 keV transition of the “Fe nucleus. In order to obtain the orientations of the magnetic moments w.r.t. the ribbon plane and to the transverse (short) axis of the ribbon, the ribbon was orientated in various position w.r.t. the incident y-rays. Fig. 1 shows the relative orientations of the ribbon. Initial spectra were obtained with the ribbon plane perpendicular to the y-rays. These were used to obtain the orientation of the magnetic moments w.r.t. to the plane of the ribbon. The ribbons were then rotated 45” about its long axis and a series of spectra were recorded as the ribbons were further rotated about the plane perpenducular axis.
B,, cSi_j (C,
rihhons
The angle between the y-ray direction and the average direction of the magnetic moment can be determined from the ratio of the intensity of the second (fifth) peak to that of the first (sixth) peak from the relation [6] 4 sin2a
R-F_ l(6)
3(1 + cos*a> ’
where (Yis the angle to be determined. The intepsities of the second and first peaks in the spectra for the ribbons orientated perpendicular to the incident y-rays indicated that the anisotropy in the 594 K annealed ribbon is pointing at an angle of 12.9” out of the plane of the ribbon and that the anisotropy in the 654 K annealed ribbon is pointing at an angle of 10.28” out of the plane. The difference between the angles seen here and those reported by Saegusa and Morrish [4] is due to the fact that the ribbons used in our study were annealed in an applied magnetic field while those of Saegusa and Morrish were not. Fig. 2 shows the intensity ratios as the tilted ribbons were rotated about the x’ axis (through an angle -cp). Since the orientation of the magnetic moment is fixed w.r.t. the ribbon, the angle between the direction of the y-rays and the magnetic moment will change as the ribbon is being rotated according to the relation cos (Y= cos 45” cos 8, + sin 45” sin tIM cos( cp + cpO),
Fig. 1. Orientation of the ribbon with respect to the incident y-rays. 45” gives the rotation of the ribbon about its longitudinal axis. cp gives the rotation of the ribbon about an axis perpendicular to the ribbon planes.
where 13~ is the angle between the magnetic moment and the x’ axis and which can be determined from the intensity ratios for the ribbon perpendicular to the y-rays. The 45” angle is the angle through which the ribbon was rotated about its longitudinal axis. cp and ‘p,, are the angles the projections of the y-ray direction and magnetic moment on the y/-z’ plane make with the transverse axis of the ribbon. As is evident from the relation, cos’a increases and decreases as the ribbon is rotated. The maximum value of COS’CX occurs when cp + ‘pO is equal to zero. For the occasion where sin eM > cos OM, a second maximum in the values of cos2a occurs when ‘p + ‘pO= 180”. The minimum in the intensity ratio R occurs when COS’OL are at their maxima. Thus the orientation of
T. Methasiri
et (11./ In -plane anisorropy in a-Fe,,
0
B,, ,Si 1.J,
231
ribbons
0
0 1.1
0 0
R
l
l
l
0
0 l
0000
654
*orno
594
K K
l 0
_(
‘i 0
-5
0
40
80
120
160
200
DEGREE
Fig. 2. Ratio of the intensity of the second (fifth) peak to that of the first (sixth) peak for various minima give the off-axis orientation of the magnetization in the plane of the ribbon.
the projections of the magnetic moment in the ribbon plane can be determined directly from the position of the minima in fig. 2. According to fig. 2, the in-plane component of the magnetic moment is (17 k 5)” off the transverse axis for the 594 K annealed specimen and (10 k 5)” for the 654 K annealed ribbon. These values, along with the values of the out of plane directions of the magnetic moment, indicate that there is a progression towards complete transverse alignment as the annealing temperature is increased. The alignment of the anisotropy in the amorphous ribbons can be understood in terms of the mixed anisotropy model in which an internal stress pointing at some angle off the longitudinal axis (21” for the case of Fe,,B,, (METGLAS 2605) ribbons [7]), the field induced stress pointing along the transverse axis and the compressive stress compete in providing an easy axis of magnetiza-
240 B
angles.
The odd positions
of the
tion in the ribbon while the ribbon is being annealed. It is interesting to note that when the ribbon is annealed at 680 K in the absence of a field, only a slight rotation of the in plane component of the moment towards the y’ axis is observed [8]. This latter behavior could be caused by a relaxation of the stress along the longitudinal direction due to the annealing or because by the crystallization at the surface which occurs for 660 K < TA < 710 K [4]. Returning to our observations, the difference in the off the transverse axis alignments for the 594 and 654 K annealed ribbons could be related to the difference in the coupling factors for the two specimens. Since the coupling factor for the 654 K ribbon,is higher than that of the 594 K specimen [l], it would be easier for the magnetic anisotropy in the 654 K specimen to rotate (and thus align itself) in the direction of the field induced stress. We cannot rule out a role
232
T. Methasirr et al. / In
-planeanisotropy in a-Fe,, B, i _7Si,,,C, ribbons
for the precrystallizatioo rearrangement of the atoms which takes place when 620 K < TA -C685 K [2,3.5] in bringing about the transverse axis alignment. We hope that our observations can contribute to a better understanding of the magnetic anisotropy existing in amorphous ribbons.
Acknowledgements The Mossbauer measurements were carried out at the American University, Washington DC by T. Methasiri. He would like to thank Dr. E. Callen for the hospitality shown to him and Dr. C. Bucci for valuable disccussions.
References [l] C. Modzelewski, H.T. Savage. L.T. Kabacoff and A.E. Clark, IEEE Trans. Magn. MAG-17 (1981) 2837. [2] N. Saegusa and A.H. Morrish. Phys. Rev. B26 (1982) 10. [3] N. Saegusa and A.H. Morrish. Phys. Rev. B26 (1982) 305, 6547, B27 (1983) 4027. [4] A.K. Bhatnagar, B.B. Prasad and R. Jagannathan, Phys. Rev. B29 (1984) 4896. [S] N. Saegusa and A.H. Morrish, J. Magn. Magn. Mat. 31-34 (1983) 1555. [6] H.N. Ok and A.H. Morrish, Phys. Rev. B23 (1981) 2257, B22 (1980) 4215. [7] L. Dwynn Lafleur, Phys. Rev. 820 (1979) 2581. [8] C. Bucci, T. Methasiri, A.E. Clark and H.T. Savage, J. Appl. Phys. 53 (1982) 2670.
MiiSSBAUER Fe,, B &3i
Materials
STUDY
229
53 (1985) 229-232
OF THE
IN-PLANE
ANISOTROPY
IN ANNEALED
AMORPHOUS
3,5Cz RIBBONS
T. METHASIRI Physics Department,
Chulalongkorn
University, Bungkok
10500, Thailund
J.R. CULLEN Naval Surface
Weapon Center, White Oak, Silver Spring, MD 20910, USA
and I.M. TANG Physics Department, Received
Mahidol
University, Bangkok
10400, Thailand
10 April 1985; in revised form 26 July 1985
MGssbauer spectra of amorphous Fe,,B,,,, Si 3 s C z ribbons (METGLAS 2605 SC) annealed in transverse magnetic field at 594 and 654 K were recorded for various orientations of the ribbons. It is determined that the in-plane projection of the anisotropy is 17’ off the transverse axis for the 594 K annealed specimen and 10” off the transverse axis for the 654 K specimen.
Much interest has recently been shown in the quaternary amorphous alloy Fe,, B,,,,Si 3,5C, (METGLAS * 2605 SC). Modzelewski et al. [l] have measured the magnetomechanical coupling and permeability of this and other amorphous ribbons which were annealed in a magnetic field applied in the plane of the ribbon and transverse to the long axis. Saegusa and Morrish have carried out a series of Massbauer measurements on the 2605 SC ribbons in order to characterise [2] the amorphous Fe,, B,,,,Si,., Cz alloys and to understand [3] the amorphous to crystalline transformation in this alloy. Bhatnager et al. [4] have also performed Mtissbauer measurements on this amorphous alloy. Saegusa and Morrish reported that there exists a magnetic anisotropy pointing out of the plane of the ribbon. The angle at which the anisotropy points out of the plane depends on the heat treatment of the ribbon after it is casted. Saegusa and * METGLAS Corp.
is a registered
trademark
of the Allied Chemical
0304-8853/85/$03.30 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
Morrish [5] found the magnetic moment to be pointing at an average angle of 20” from the ribbon plane when the annealing temperature TA was less than 620 K. When TA was increased from 620 to 685 K, the average angle increased slowly to about 55”. An abrupt decrease to an apparent angle of 35” was observed as TA was increased from 685 to 690 K at which crystallization started to occur. The angle is an apparent one since the magnetic moments are randomly oriented once crystallization sets in. The formation of the anisotropy pointing out of the plane of the ribbon can be accounted for by the model used by Ok and Morrish [6] to explain the out-of-plane anisotropy of the magnetization in the amorphous Fe,,B,,Si, alloy (METGLAS 2605 C). The differences in the directions of the anisotropy in the 2605 SC ribbons for TA below 620 K and for TA between 620 and 685 K are probably due to the differences in the compressive stress in the ribbon caused by the differing atomic rearrangements which are occurring in the two annealing regions [41. B.V.
230
T. Merhasirr
et al. / In -plane
misotrop_); in (1-Fe,,
The purpose of this note is to report our measurements of the Mossbauer effect in a field annealed Fe,, B,,,,Si 3,5C, ribbon which indicate a difference in the direction of the projection of the magnetic moment in the plane of the ribbon when the ribbons are annealed in a transverse field (> 2 kOe) at 594 and 654 K for 20 min durations. A standard Mossbauer spectrometer using 57Co in Pd as source was used to obtain the six peak patterns expected of the hyperfine split 14.4 keV transition of the “Fe nucleus. In order to obtain the orientations of the magnetic moments w.r.t. the ribbon plane and to the transverse (short) axis of the ribbon, the ribbon was orientated in various position w.r.t. the incident y-rays. Fig. 1 shows the relative orientations of the ribbon. Initial spectra were obtained with the ribbon plane perpendicular to the y-rays. These were used to obtain the orientation of the magnetic moments w.r.t. to the plane of the ribbon. The ribbons were then rotated 45” about its long axis and a series of spectra were recorded as the ribbons were further rotated about the plane perpenducular axis.
B,, cSi_j (C,
rihhons
The angle between the y-ray direction and the average direction of the magnetic moment can be determined from the ratio of the intensity of the second (fifth) peak to that of the first (sixth) peak from the relation [6] 4 sin2a
R-F_ l(6)
3(1 + cos*a> ’
where (Yis the angle to be determined. The intepsities of the second and first peaks in the spectra for the ribbons orientated perpendicular to the incident y-rays indicated that the anisotropy in the 594 K annealed ribbon is pointing at an angle of 12.9” out of the plane of the ribbon and that the anisotropy in the 654 K annealed ribbon is pointing at an angle of 10.28” out of the plane. The difference between the angles seen here and those reported by Saegusa and Morrish [4] is due to the fact that the ribbons used in our study were annealed in an applied magnetic field while those of Saegusa and Morrish were not. Fig. 2 shows the intensity ratios as the tilted ribbons were rotated about the x’ axis (through an angle -cp). Since the orientation of the magnetic moment is fixed w.r.t. the ribbon, the angle between the direction of the y-rays and the magnetic moment will change as the ribbon is being rotated according to the relation cos (Y= cos 45” cos 8, + sin 45” sin tIM cos( cp + cpO),
Fig. 1. Orientation of the ribbon with respect to the incident y-rays. 45” gives the rotation of the ribbon about its longitudinal axis. cp gives the rotation of the ribbon about an axis perpendicular to the ribbon planes.
where 13~ is the angle between the magnetic moment and the x’ axis and which can be determined from the intensity ratios for the ribbon perpendicular to the y-rays. The 45” angle is the angle through which the ribbon was rotated about its longitudinal axis. cp and ‘p,, are the angles the projections of the y-ray direction and magnetic moment on the y/-z’ plane make with the transverse axis of the ribbon. As is evident from the relation, cos’a increases and decreases as the ribbon is rotated. The maximum value of COS’CX occurs when cp + ‘pO is equal to zero. For the occasion where sin eM > cos OM, a second maximum in the values of cos2a occurs when ‘p + ‘pO= 180”. The minimum in the intensity ratio R occurs when COS’OL are at their maxima. Thus the orientation of
T. Methasiri
et (11./ In -plane anisorropy in a-Fe,,
0
B,, ,Si 1.J,
231
ribbons
0
0 1.1
0 0
R
l
l
l
0
0 l
0000
654
*orno
594
K K
l 0
_(
‘i 0
-5
0
40
80
120
160
200
DEGREE
Fig. 2. Ratio of the intensity of the second (fifth) peak to that of the first (sixth) peak for various minima give the off-axis orientation of the magnetization in the plane of the ribbon.
the projections of the magnetic moment in the ribbon plane can be determined directly from the position of the minima in fig. 2. According to fig. 2, the in-plane component of the magnetic moment is (17 k 5)” off the transverse axis for the 594 K annealed specimen and (10 k 5)” for the 654 K annealed ribbon. These values, along with the values of the out of plane directions of the magnetic moment, indicate that there is a progression towards complete transverse alignment as the annealing temperature is increased. The alignment of the anisotropy in the amorphous ribbons can be understood in terms of the mixed anisotropy model in which an internal stress pointing at some angle off the longitudinal axis (21” for the case of Fe,,B,, (METGLAS 2605) ribbons [7]), the field induced stress pointing along the transverse axis and the compressive stress compete in providing an easy axis of magnetiza-
240 B
angles.
The odd positions
of the
tion in the ribbon while the ribbon is being annealed. It is interesting to note that when the ribbon is annealed at 680 K in the absence of a field, only a slight rotation of the in plane component of the moment towards the y’ axis is observed [8]. This latter behavior could be caused by a relaxation of the stress along the longitudinal direction due to the annealing or because by the crystallization at the surface which occurs for 660 K < TA < 710 K [4]. Returning to our observations, the difference in the off the transverse axis alignments for the 594 and 654 K annealed ribbons could be related to the difference in the coupling factors for the two specimens. Since the coupling factor for the 654 K ribbon,is higher than that of the 594 K specimen [l], it would be easier for the magnetic anisotropy in the 654 K specimen to rotate (and thus align itself) in the direction of the field induced stress. We cannot rule out a role
232
T. Methasirr et al. / In
-planeanisotropy in a-Fe,, B, i _7Si,,,C, ribbons
for the precrystallizatioo rearrangement of the atoms which takes place when 620 K < TA -C685 K [2,3.5] in bringing about the transverse axis alignment. We hope that our observations can contribute to a better understanding of the magnetic anisotropy existing in amorphous ribbons.
Acknowledgements The Mossbauer measurements were carried out at the American University, Washington DC by T. Methasiri. He would like to thank Dr. E. Callen for the hospitality shown to him and Dr. C. Bucci for valuable disccussions.
References [l] C. Modzelewski, H.T. Savage. L.T. Kabacoff and A.E. Clark, IEEE Trans. Magn. MAG-17 (1981) 2837. [2] N. Saegusa and A.H. Morrish. Phys. Rev. B26 (1982) 10. [3] N. Saegusa and A.H. Morrish. Phys. Rev. B26 (1982) 305, 6547, B27 (1983) 4027. [4] A.K. Bhatnagar, B.B. Prasad and R. Jagannathan, Phys. Rev. B29 (1984) 4896. [S] N. Saegusa and A.H. Morrish, J. Magn. Magn. Mat. 31-34 (1983) 1555. [6] H.N. Ok and A.H. Morrish, Phys. Rev. B23 (1981) 2257, B22 (1980) 4215. [7] L. Dwynn Lafleur, Phys. Rev. 820 (1979) 2581. [8] C. Bucci, T. Methasiri, A.E. Clark and H.T. Savage, J. Appl. Phys. 53 (1982) 2670.