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Structural and magnetic studies of the alloy system CuAl1−xFex
Journal of Magnetism and Magnetic Materials 99 (1991) 152-158 North-Holland
Structural and magnetic studies of the alloy system CuAl,_,Fe, A.S. Saleh,
R. Al-Jaber,
A. Malkawi,
S. M&mood
and I. Abu-Aljarayesh
Department of Physics, Yarmouk University, Irbid, Jordan Received 28 March 1991
We report structural and magnetic measurements on the alloy system CuAl, _xFex for x = 0.1, 0.2, 0.3 and 0.4. The results have shown that the system is a multiphase one for all values of x. At x I 0.2, a dominant CuAl phase with a B2 structure and a significantly weaker B2-FeAl phase exist. As x increases (x > 0.2) the FeAl phase grows stronger and the CuAl phase disappears, giving rise to the cubic y2-CugA14 phase, and then to the orthorhombic B,‘-CusAl phase for x 2 0.4. The development of the magnetic properties as x increases seems to be consistent with the above structural changes. At low values of x a dominant diamagnetic response was observed and was associated with the CuAl phase. As x increases (x > 0.2) the paramagnetic signal of the FeAl phase dominates, and becomes superparamagnetic for x 2 0.4, indicating an Fe-rich FeAl phase. In addition, a weak ferromagnetic component was observed for x s 0.2, and was associated with traces of Fe-rich clusters.
1. Introduction Transition metal alloys have attracted a lot of interest due to their potential technical applications and to their role in leading to a better understanding of the theory of magnetism [l]. The substitution of a 3d metal for Al in FeAl [2,3] or in CoAl [4], and for Ga in CoGa [5] is known to produce changes in the magnetic and structural properties of these alloys. In particular, the cubic system FeAl, _$ux of the B2 type shows ferromagnetic order beyond a critical concentration x, = 0.25, and the development of new structural phases beyond x = 0.35 [3]. The role of Cu substitution in producing these changes may be further investigated by studying the structural and magnetic properties of the related alloy system CuAl,_,Fe, as the concentration of Fe is increased. In this paper we present the results of a systematic study of CuAl, _,Fe, using magnetization measurements and X-ray diffraction techniques. 2. Experimental The alloys were prepared by arc melting the proper amounts of the spec-pure metals in an 0304-8853/91/$03.50
argon atmosphere. The heat treatment of the alloys is similar to that described in ref. [2]. The measurements were made on powdered samples except for the alloy with x = 0.4 which was difficult to crush. A small ellipsoidal sample was prepared from this alloy for magnetization measurements, and a thin polished flat section was used for X-ray scans. Magnetization measurements were taken using the standard force method (Faraday balance). Powder X-ray diffraction patterns were obtained using a computerized Philips 8-28 diffractometer. 3. Results 3.1. Structural X-ray diffraction patterns for CuAl,_,Fe, alloys have shown that this is a multi-phase system for values of x in the range 0.1 I x I 0.5. Analysis of these patterns indicates that two ordered B2 phases exist for x < 0.3. The first one showing strong diffraction peaks has a lattice parameter a = 2.94 A. This value of a is in good agreement with that observed for CuAl [6,7]. The second one with considerably weaker diffraction peaks has a lattice parameter a = 2.89 A which is in good
0 1991 - Elsevier Science Publishers B.V. All rights reserved
A.S. Saleh et al. / Properties
agreement with that of the FeAl alloy. In the alloy with x = 0.3 the diffraction pattern indicates that the ordered FeAl (B2) phase grows stronger, while the CuAl phase disappears and a triply ordered cubic phase with a lattice parameter equal to 8.67 A is observed. This value of the lattice parameter is in agreement with that of the cubic y&u,Al, phase [7]. For x > 0.3 the FeAl phase persists, the y2 phase becomes weaker and disappears at x = 0.5, and a new orthorhombic Pi-Cu,Al phase develops [ 71. 3.2. Magnetic Magnetization isotherms were obtained for the samples with values of x = 0.1, 0.2, 0.3 and 0.4 over the temperature range 65 K < T-c 500 K and in fields of up to 1.5 T (see figs. l-4). Fig. 1 shows that the magnetization for the sample with x = 0.1 grows to a small positive
of &AI,
153
_ x Fe, alloys
value at low fields and then starts to decrease linearly with the field at about 1 kOe. This linear part has a constant negative slope at all temperatures. This behavior is the net result of two magnetic components: one is diamagnetic and another is ferromagnetic with a small saturation magnetization (MS). The magnetization curves for the sample with x = 0.2 (fig. 2) suggest the existence of a ferromagnetic phase with a small MS and a paramagnetic phase with a relatively small susceptibility. The data for the sample with x = 0.3 (fig. 3) show paramagnetic behavior with a magnetization which is about three orders of magnitude larger than that for the previous sample. The results for the sample with x = 0.4 (fig. 4) indicate superparamagnetic behavior. At low temperature and high fields we were unable to measure the signal because it exceeds the capacity of the Faraday balance.
K K K K K
?
1
I
0
.2
.4
.a
.a
MAGNETIC FIELD
1
(Tesla)
Fig. 1. Magnetization curves for the sample with x = 0.1.
1.2
1.4
1.8
154
A.S. Saleh et al. / Properties of &AI,
_ x Fe, alloys
cu*b*oFeo.,o
*-#-*
_*/--*
/*
1
_*--+--
--At -44
*---*-
*-*-
--Y
*-*--*-*--+
-g---“/*-Y-+-
85K 100 K 120K
-* s----s
_-*-+--++
.---*
cc*-
160 200 * 250 300
-*-------~-~-*-* c-*-*-*-*-*-*-
_*_*-++-*-*
65K
*/-+-----*
-*-*-+6-s-* c-*-* -*-*-*-*-*-**
K K K i K
04 0
.2
.4
.8
.B
1
MAGNETIC FIELD Fig. 2. Magnetization
.4
.8
1. 4
1.8
1.8
(Tosla)
curves for the sample with x = 0.2
.a
1
MAGNETIC FIELD Fig. 3. Magnetization
1.2
1.2
(Tesld
curves for the sample with x = 0.3.
1. 4
1.6
1.0
A.S. Saleh et al. / Properties of CuA1, _ x Fe, alloys
.4
.6
.e
MAGNETIC Fig. 4. Magnetization
1
155
1.2
FIELD
curves for the sample with x = 0.4.
65 K
_*-~*-*-*-*~-*-*----k
-Q-c9---~-Q-O
Y”--a-
m-m-m-m-m-
m-m-m-
LO_ &
acl-m
200 K
Q -_6-Q-Q
Q---_o-e-----9._u--A-.-p4--l_.
CU *\ .Pfeo,,’
150K
250K Q
ferro.
Phase
0
0
.2
.4
.6
.a
MAGNETIC Fig. 5. Ferromagnetic
FIELD
1
(Tesla)
phase for the sample with x = 0.1.
1.2
1.4
156
A.S. Saleh et al. / Properties of &AI,
4. Analysis and discussion
increasing slope as T is decreased. This behavior is consistent with the existence of two superimposed phases: a paramagnetic phase with a susceptibility that increases as the temperature is decreased and a ferromagnetic component with small M,. The paramagnetic component is obtained by drawing a straight line parallel to the experimental curve at high fields and passing through the origin (fig. 6). Subtracting this component from the experimental curve, we obtain the ferromagnetic component which may be associated with Fe-rich clusters, as in the previous sample. The paramagnetic component, however, is the net result of the contributions of the two cubic phases, observed in the X-ray diffraction pattern of this alloy: the diamagnetic CuAl and the paramagnetic FeAl. The magnitudes of these two contributions seem to be of the same order. The weakness of the paramagnetic contribution of the FeAl phase (= 10W3 Am*/kg) may be due to two factors: the small relative proportion of this phase in the alloy, and the possibility that this phase is Al-rich [B].
Structural and magnetic results (section 3) indicate that the alloy series Ct~4l,_~Fe, is a multiphase system for all values of x. The existence of more than one phase is most probably related to the annealing process. In the alloy with x = 0.1 both structural and magnetic data consist mainly of the diamagnetic CuAl cubic (B2) phase. The magnetic data also show the existence of a weak ferromagnetic phase which may be associated with very small amounts of Fe-rich clusters which are difficult to detect by X-rays. The temperature-independent contribution of the diamagnetic phase to the sample magnetization is obtained by drawing a straight line parallel to the experimental curve at high fields and passing through the origin. This contribution is then subtracted from the experimental curve to obtain the magnetization of the ferromagnetic phase (see fig. 5). The magnetization curves for the alloy with x = 0.2 (fig. 2) show a quick rise at low fields, followed by a linear region which has a gradually
m
Cu AL . 6feo2 .
-
0
_ x Fe, alloys
.2
.A
.6
.6
MAGNETIC
Fig. 6. Paramagnetic
1
FIELD
1.2
(Tesld
phase for the sample with x = 0.2.
1.4
1.6
1.6
A.S. Saleh et al. / Properties of &AI,
_ x Fe, alloys
157
CuAI,,,Fe,, . .
0
*
//
i
*
*
-
m
/ *
/ *
N
/
-
/* *
,’
*3
/
a
wn
2M
TEMPERATURE Fig. 7. Inverse susceptibility
CuAl
OS6
vs. temperature
400
so0
SW
( K 1 for the sample with x = 0.3.
Fe
0.4
*
*
65
K
a
100K
o 200 K 6 300 K . 400 K _
10
20
30
H/T Fig. 8. Langevin
40
CO&K1
curve for the sample with x = 0.4.
!I0
Theor.
60
158
A. S. Saleh et al. / Properties of CuA I,
The magnetization data for the alloy x = 0.3 (fig. 3) show a single paramagnetic phase which is associated with FeAl. The y,-Cu,Al, phase observed in the X-ray data is diamagnetic [9] and its contribution is clearly dominated by that of the paramagnetic phase. A plot of inverse susceptibility x-i versus T for this phase (fig. 7) gives an effective magnetic moment of pFl,rr = 4.6~~ and a paramagnetic temperature 0, = 33 K. These results are in good agreement with those of other workers [lo]. The results for the alloy with x = 0.4 (fig. 4) show that the susceptibility is field-dependent and the magnetization does not saturate. However, the saturation magnetization at each temperature was obtained by extrapolating the M versus l/H curves. A Langevin plot (M/M, vs. H/T) normalized at H/T = 35 Oe/K was then best-fitted through the experimental points (fig. 8) indicating superparamagnetic behavior. From this fitting, an average magnetic moment of p = 1300~s per magnetic particle was obtained and an average particle radius of 35 A was estimated. The superparamagnetic behavior in this alloy is most probably associated with B2 FeAl phase observed in the X-ray patterns and indicates that this phase is Fe-rich. It is also possible that the Al in this phase is partially substituted by Cu. This possibility is based on the fact that superparamagnetic behavior was also observed in FeAl, _$Zu, [3]. In conclusion, it has been established that as Fe gradually replaces Al in the alloy CuAl a new FeAl phase develops, and the B2 CuAl phase transforms into the y,-Cu,Al, phase and then into the orthorhombic &‘-Cu,Al phase. In addition, the magnetic properties of this system
*Fe, alloys
change from diamagnetic at low x-values to paramagnetic and then to superparamagnetic as the concentration of Fe increases. These magnetic changes follow the evolution of the FeAl phase whose magnetic contribution becomes the dominant one for x 2 0.3. These properties of CuAl, _,Fe, are consistent with those of the alloy system FeAl,_,Cu, in the region of high Cu concentration where different phases coexist in both systems.
References [l] M. Cyrot, Magnetism of Metals and Alloys (North-Holland, Amsterdam, 1982). T. Moriya, J. Magn. Magn. Mater. 14 (1979) 1. J.M. Franz and D.J. Sellmyer, Phys. Rev. B 8 (1973) 2083. [2] D.E. Okpalugo, J.G. Booth and C.A. Faunce, J. Phys. F 15 (1985) 681. D.E. Okpalugo and J.G. Booth, J. Phys. F 15 (1985) 2025. [3] AS. Saleh, R.M. Mankikar, S. Yoon, D.E. Okpalugo and J.G. Booth, J. Appl. Phys. 57 (1985) 3241. [41A.S. Saleh, R.M. Mankikar and J.G. Booth, J. Appl. Phys. 61 (1987) 4243. J.G. Booth, R.M. Mankikar and A.S. Saleh, J. de Phys. 49 (1988) C8-153. I51J.G. Booth and R.G. Pritchard, J. Phys. F 5 (1975) 374. J.G. Booth, R. Cywinski and J.G. Prince, J. Magn. Magn. Mater. 7 (1978) 127. 161 P. Brezina, Intern. Met. Rev. 27 (1982) 77. and C.W. Draper, Mater. Lett. 2 (1984) 171J.M. Vandenberg 386. T. Abu Sneineh and A. Saleh, (to be pubPI S. Mahmood, lished). Recent Mossbauer study of this alloy have shown (from isomer shift measurements) that Fe is surrounded by an Al-rich environment. V.B. Kiselev and V.M. Skorikov, Inorg. [91V.A. Kutvitskii, Mater. (USA) 13 (1977) 953. WI H. Domke and L.K. Thomas, J. Magn. Magn. Mater. 45 (1984) 305.
Structural and magnetic studies of the alloy system CuAl,_,Fe, A.S. Saleh,
R. Al-Jaber,
A. Malkawi,
S. M&mood
and I. Abu-Aljarayesh
Department of Physics, Yarmouk University, Irbid, Jordan Received 28 March 1991
We report structural and magnetic measurements on the alloy system CuAl, _xFex for x = 0.1, 0.2, 0.3 and 0.4. The results have shown that the system is a multiphase one for all values of x. At x I 0.2, a dominant CuAl phase with a B2 structure and a significantly weaker B2-FeAl phase exist. As x increases (x > 0.2) the FeAl phase grows stronger and the CuAl phase disappears, giving rise to the cubic y2-CugA14 phase, and then to the orthorhombic B,‘-CusAl phase for x 2 0.4. The development of the magnetic properties as x increases seems to be consistent with the above structural changes. At low values of x a dominant diamagnetic response was observed and was associated with the CuAl phase. As x increases (x > 0.2) the paramagnetic signal of the FeAl phase dominates, and becomes superparamagnetic for x 2 0.4, indicating an Fe-rich FeAl phase. In addition, a weak ferromagnetic component was observed for x s 0.2, and was associated with traces of Fe-rich clusters.
1. Introduction Transition metal alloys have attracted a lot of interest due to their potential technical applications and to their role in leading to a better understanding of the theory of magnetism [l]. The substitution of a 3d metal for Al in FeAl [2,3] or in CoAl [4], and for Ga in CoGa [5] is known to produce changes in the magnetic and structural properties of these alloys. In particular, the cubic system FeAl, _$ux of the B2 type shows ferromagnetic order beyond a critical concentration x, = 0.25, and the development of new structural phases beyond x = 0.35 [3]. The role of Cu substitution in producing these changes may be further investigated by studying the structural and magnetic properties of the related alloy system CuAl,_,Fe, as the concentration of Fe is increased. In this paper we present the results of a systematic study of CuAl, _,Fe, using magnetization measurements and X-ray diffraction techniques. 2. Experimental The alloys were prepared by arc melting the proper amounts of the spec-pure metals in an 0304-8853/91/$03.50
argon atmosphere. The heat treatment of the alloys is similar to that described in ref. [2]. The measurements were made on powdered samples except for the alloy with x = 0.4 which was difficult to crush. A small ellipsoidal sample was prepared from this alloy for magnetization measurements, and a thin polished flat section was used for X-ray scans. Magnetization measurements were taken using the standard force method (Faraday balance). Powder X-ray diffraction patterns were obtained using a computerized Philips 8-28 diffractometer. 3. Results 3.1. Structural X-ray diffraction patterns for CuAl,_,Fe, alloys have shown that this is a multi-phase system for values of x in the range 0.1 I x I 0.5. Analysis of these patterns indicates that two ordered B2 phases exist for x < 0.3. The first one showing strong diffraction peaks has a lattice parameter a = 2.94 A. This value of a is in good agreement with that observed for CuAl [6,7]. The second one with considerably weaker diffraction peaks has a lattice parameter a = 2.89 A which is in good
0 1991 - Elsevier Science Publishers B.V. All rights reserved
A.S. Saleh et al. / Properties
agreement with that of the FeAl alloy. In the alloy with x = 0.3 the diffraction pattern indicates that the ordered FeAl (B2) phase grows stronger, while the CuAl phase disappears and a triply ordered cubic phase with a lattice parameter equal to 8.67 A is observed. This value of the lattice parameter is in agreement with that of the cubic y&u,Al, phase [7]. For x > 0.3 the FeAl phase persists, the y2 phase becomes weaker and disappears at x = 0.5, and a new orthorhombic Pi-Cu,Al phase develops [ 71. 3.2. Magnetic Magnetization isotherms were obtained for the samples with values of x = 0.1, 0.2, 0.3 and 0.4 over the temperature range 65 K < T-c 500 K and in fields of up to 1.5 T (see figs. l-4). Fig. 1 shows that the magnetization for the sample with x = 0.1 grows to a small positive
of &AI,
153
_ x Fe, alloys
value at low fields and then starts to decrease linearly with the field at about 1 kOe. This linear part has a constant negative slope at all temperatures. This behavior is the net result of two magnetic components: one is diamagnetic and another is ferromagnetic with a small saturation magnetization (MS). The magnetization curves for the sample with x = 0.2 (fig. 2) suggest the existence of a ferromagnetic phase with a small MS and a paramagnetic phase with a relatively small susceptibility. The data for the sample with x = 0.3 (fig. 3) show paramagnetic behavior with a magnetization which is about three orders of magnitude larger than that for the previous sample. The results for the sample with x = 0.4 (fig. 4) indicate superparamagnetic behavior. At low temperature and high fields we were unable to measure the signal because it exceeds the capacity of the Faraday balance.
K K K K K
?
1
I
0
.2
.4
.a
.a
MAGNETIC FIELD
1
(Tesla)
Fig. 1. Magnetization curves for the sample with x = 0.1.
1.2
1.4
1.8
154
A.S. Saleh et al. / Properties of &AI,
_ x Fe, alloys
cu*b*oFeo.,o
*-#-*
_*/--*
/*
1
_*--+--
--At -44
*---*-
*-*-
--Y
*-*--*-*--+
-g---“/*-Y-+-
85K 100 K 120K
-* s----s
_-*-+--++
.---*
cc*-
160 200 * 250 300
-*-------~-~-*-* c-*-*-*-*-*-*-
_*_*-++-*-*
65K
*/-+-----*
-*-*-+6-s-* c-*-* -*-*-*-*-*-**
K K K i K
04 0
.2
.4
.8
.B
1
MAGNETIC FIELD Fig. 2. Magnetization
.4
.8
1. 4
1.8
1.8
(Tosla)
curves for the sample with x = 0.2
.a
1
MAGNETIC FIELD Fig. 3. Magnetization
1.2
1.2
(Tesld
curves for the sample with x = 0.3.
1. 4
1.6
1.0
A.S. Saleh et al. / Properties of CuA1, _ x Fe, alloys
.4
.6
.e
MAGNETIC Fig. 4. Magnetization
1
155
1.2
FIELD
curves for the sample with x = 0.4.
65 K
_*-~*-*-*-*~-*-*----k
-Q-c9---~-Q-O
Y”--a-
m-m-m-m-m-
m-m-m-
LO_ &
acl-m
200 K
Q -_6-Q-Q
Q---_o-e-----9._u--A-.-p4--l_.
CU *\ .Pfeo,,’
150K
250K Q
ferro.
Phase
0
0
.2
.4
.6
.a
MAGNETIC Fig. 5. Ferromagnetic
FIELD
1
(Tesla)
phase for the sample with x = 0.1.
1.2
1.4
156
A.S. Saleh et al. / Properties of &AI,
4. Analysis and discussion
increasing slope as T is decreased. This behavior is consistent with the existence of two superimposed phases: a paramagnetic phase with a susceptibility that increases as the temperature is decreased and a ferromagnetic component with small M,. The paramagnetic component is obtained by drawing a straight line parallel to the experimental curve at high fields and passing through the origin (fig. 6). Subtracting this component from the experimental curve, we obtain the ferromagnetic component which may be associated with Fe-rich clusters, as in the previous sample. The paramagnetic component, however, is the net result of the contributions of the two cubic phases, observed in the X-ray diffraction pattern of this alloy: the diamagnetic CuAl and the paramagnetic FeAl. The magnitudes of these two contributions seem to be of the same order. The weakness of the paramagnetic contribution of the FeAl phase (= 10W3 Am*/kg) may be due to two factors: the small relative proportion of this phase in the alloy, and the possibility that this phase is Al-rich [B].
Structural and magnetic results (section 3) indicate that the alloy series Ct~4l,_~Fe, is a multiphase system for all values of x. The existence of more than one phase is most probably related to the annealing process. In the alloy with x = 0.1 both structural and magnetic data consist mainly of the diamagnetic CuAl cubic (B2) phase. The magnetic data also show the existence of a weak ferromagnetic phase which may be associated with very small amounts of Fe-rich clusters which are difficult to detect by X-rays. The temperature-independent contribution of the diamagnetic phase to the sample magnetization is obtained by drawing a straight line parallel to the experimental curve at high fields and passing through the origin. This contribution is then subtracted from the experimental curve to obtain the magnetization of the ferromagnetic phase (see fig. 5). The magnetization curves for the alloy with x = 0.2 (fig. 2) show a quick rise at low fields, followed by a linear region which has a gradually
m
Cu AL . 6feo2 .
-
0
_ x Fe, alloys
.2
.A
.6
.6
MAGNETIC
Fig. 6. Paramagnetic
1
FIELD
1.2
(Tesld
phase for the sample with x = 0.2.
1.4
1.6
1.6
A.S. Saleh et al. / Properties of &AI,
_ x Fe, alloys
157
CuAI,,,Fe,, . .
0
*
//
i
*
*
-
m
/ *
/ *
N
/
-
/* *
,’
*3
/
a
wn
2M
TEMPERATURE Fig. 7. Inverse susceptibility
CuAl
OS6
vs. temperature
400
so0
SW
( K 1 for the sample with x = 0.3.
Fe
0.4
*
*
65
K
a
100K
o 200 K 6 300 K . 400 K _
10
20
30
H/T Fig. 8. Langevin
40
CO&K1
curve for the sample with x = 0.4.
!I0
Theor.
60
158
A. S. Saleh et al. / Properties of CuA I,
The magnetization data for the alloy x = 0.3 (fig. 3) show a single paramagnetic phase which is associated with FeAl. The y,-Cu,Al, phase observed in the X-ray data is diamagnetic [9] and its contribution is clearly dominated by that of the paramagnetic phase. A plot of inverse susceptibility x-i versus T for this phase (fig. 7) gives an effective magnetic moment of pFl,rr = 4.6~~ and a paramagnetic temperature 0, = 33 K. These results are in good agreement with those of other workers [lo]. The results for the alloy with x = 0.4 (fig. 4) show that the susceptibility is field-dependent and the magnetization does not saturate. However, the saturation magnetization at each temperature was obtained by extrapolating the M versus l/H curves. A Langevin plot (M/M, vs. H/T) normalized at H/T = 35 Oe/K was then best-fitted through the experimental points (fig. 8) indicating superparamagnetic behavior. From this fitting, an average magnetic moment of p = 1300~s per magnetic particle was obtained and an average particle radius of 35 A was estimated. The superparamagnetic behavior in this alloy is most probably associated with B2 FeAl phase observed in the X-ray patterns and indicates that this phase is Fe-rich. It is also possible that the Al in this phase is partially substituted by Cu. This possibility is based on the fact that superparamagnetic behavior was also observed in FeAl, _$Zu, [3]. In conclusion, it has been established that as Fe gradually replaces Al in the alloy CuAl a new FeAl phase develops, and the B2 CuAl phase transforms into the y,-Cu,Al, phase and then into the orthorhombic &‘-Cu,Al phase. In addition, the magnetic properties of this system
*Fe, alloys
change from diamagnetic at low x-values to paramagnetic and then to superparamagnetic as the concentration of Fe increases. These magnetic changes follow the evolution of the FeAl phase whose magnetic contribution becomes the dominant one for x 2 0.3. These properties of CuAl, _,Fe, are consistent with those of the alloy system FeAl,_,Cu, in the region of high Cu concentration where different phases coexist in both systems.
References [l] M. Cyrot, Magnetism of Metals and Alloys (North-Holland, Amsterdam, 1982). T. Moriya, J. Magn. Magn. Mater. 14 (1979) 1. J.M. Franz and D.J. Sellmyer, Phys. Rev. B 8 (1973) 2083. [2] D.E. Okpalugo, J.G. Booth and C.A. Faunce, J. Phys. F 15 (1985) 681. D.E. Okpalugo and J.G. Booth, J. Phys. F 15 (1985) 2025. [3] AS. Saleh, R.M. Mankikar, S. Yoon, D.E. Okpalugo and J.G. Booth, J. Appl. Phys. 57 (1985) 3241. [41A.S. Saleh, R.M. Mankikar and J.G. Booth, J. Appl. Phys. 61 (1987) 4243. J.G. Booth, R.M. Mankikar and A.S. Saleh, J. de Phys. 49 (1988) C8-153. I51J.G. Booth and R.G. Pritchard, J. Phys. F 5 (1975) 374. J.G. Booth, R. Cywinski and J.G. Prince, J. Magn. Magn. Mater. 7 (1978) 127. 161 P. Brezina, Intern. Met. Rev. 27 (1982) 77. and C.W. Draper, Mater. Lett. 2 (1984) 171J.M. Vandenberg 386. T. Abu Sneineh and A. Saleh, (to be pubPI S. Mahmood, lished). Recent Mossbauer study of this alloy have shown (from isomer shift measurements) that Fe is surrounded by an Al-rich environment. V.B. Kiselev and V.M. Skorikov, Inorg. [91V.A. Kutvitskii, Mater. (USA) 13 (1977) 953. WI H. Domke and L.K. Thomas, J. Magn. Magn. Mater. 45 (1984) 305.