- Email: [email protected]
Lattice parameters and magnetic properties of F-Sb-Te alloys with nickel arsenide structure
January
1998
Materials Letters 33 (1998) 261-264
ELSEVIER
Lattice parameters and magnetic properties of F-Sb-Te with nickel arsenide structure A. Rais a,*, P. Terzieff a Phwics
Department. b Institute
b, A.A. Yousif a, A.M. Gismelseed
College of Science, Sultan Qaboos lJnirersi@,
P.O. Box 36, Alkhod,
of Inorganic
Vienna, Austria
Received
Chemistp,
Uniwrrit.v
10 April 1997; accepted
of Vienna,
alloys a
Oman
15 April 1997
Abstract Single
phase
Fe-Sb-Te
alloys
with NiAs-type
structure
have been
PACS: 75.30.-m;
Keywords:
75.50.-y
Fe-Sb-Te
alloys; NiAs-type
structure;
Lattice parameters;
1. Introduction The Fe,,,,,Sb and Fe ,,,osTe binary phases have an NiAs-type structure which is basically a HCP matrix where iron atoms occupy the octahedral and bipyramidal interstices [ 1,2]. The deviations from ideal stoichiometry arise because vacant iron sites give rise to wide ranges of stability. The magnetism of Sb has been investigated by several workers E$j using different techniques. Magnetic susceptibility measurements [5] and MBssbauer spectroscopy [3] for 0.13 < x < 0.33 showed that the alloys are antiferromagnetic below a Neel temperature of 1 15
* Corresponding
in the composition range from Fe, ,73Sb to measurements have been taken on these alloys in a linear variation with the alloy composition in the effective magnetic moments extracted from the approximately the same composition. These are atomic species. 0 1998 Elsevier Science B.V.
prepared
Fe ,.,osTe and characterized by X-ray diffraction. Magnetic susceptibility the temperature range from 77 up to 500 K. The lattice parameters show Sb-rich side but an anomalous change for the binary Fe ,,,osTe. The susceptibility variations with temperature show a similar anomaly at discussed in terms of a model of additive magnetic moments of different
author. Fax: + 966-968-5 13436.
00167-577X/98/$19.00 PII 80167-577X(97)001
Magnetic
susceptibility;
Effective magnetic
moments
K varying smoothly with X. The magnetic behavior of NiAs-type Fe, _ ,,Te system suggested antiferromagnetic ordering as reported in previous papers [7-91. However, this has been confirmed by neutron diffraction and Miissbauer spectroscopy only below 10 K [lo- 121. In the composition range 0.29 < x < 0.45, the magnetic susceptibility temperature dependence of these alloys indicated two magnetically different states at high-temperature where the Ni-As phase is stable and the quenched Fe, _ lTe [8]. Owing to the mutual solubility of the binary phases, it is possible to study further the magnetic studies to ternary alloys at concentrations varying between ,,,osTe where the preparation is Fe ,.&b and Fe technically feasible.
0 1998 Elsevier Science B.V. All rights reserved 18-3
2. Experimental The alloys were prepared by direct reaction of the pure elements using Fe sheet (99.9%, Ferrovac E, Vacuum Metals Corporation, Syracuse), and lumps of antimony and tellurium (99.99%, Asarco. New York). The pre-reacted ingots were crushed and homogenised under vacuum (0.01 Pa) at suitable temperatures for a period of 2 weeks. The samples were then annealed at 900 K for 5 days before quenching. The phase purity and structures of the alloys were determined by X-ray diffraction taken using a 57.3 mm Debye-Sherrer camera and Co K,, radiation. The magnetic susceptibility measurements were performed using a Faraday analytical microbalance of 1 Fg precision. An electromagnet with specially shaped poles for constant field gradient, produced field strengths ranging from 3 up to 6 kOe. The magnet calibration was done with Mohr’s salt having a susceptibility of 32.32 X IO-” emu g ’ at 20°C. During the experiment, the sample was contained in a quartz bucket having a temperature independent diamagnetism over a wide range which could be subtracted from the measured magnetic force. An Oxford liquid nitrogen cryostat provided with a heater enabled scanning the temperatures between 77 and 500 K.
3. Results and discussion Different alloys with compositions varying from Fe I ,db ,,,oSTe have been prepared so as to to Fe keep the hexagonal (NiAs-type) structure when antimony is substituted by tellurium [ 131. The X-ray data show that all compositions have NiAs-type structure after quenching. The data analysis enabled the determination of the lattice parameTable
ters. Table I shows the results which consist of the dimensions and the volume of the unit cell together with the axial ratio C/N and the factor I (c/d/( c/a>,, which stands for the reduction in ~/LI from the ideal value (c/n>,, = 1.63. The composition of the alloys needs to be expressed in terms of iron concentration xre and tellurium atomic fraction y = xrJ( xrc + .xsb). Fig. l(a) and (b) show the lattice parameters variations with composition. Our values are in good agreement with the interpolated values of Richter et al. [3]. The anomalous behavior of a and (’ with x is not unique but has been seen in other NiAs-type ternary alloys like Fe-Co-Te [ 141. The linear change of LI and c’ can be accounted by the smaller size of Sb atoms when substituted by Te atoms. Further replacement leads to optimal values of n and c, at a composition F between 0.5 and I. The decrease of the unit cell volume V suggests that the decrease of a is faster than the increase of c. Moreover. the minima of V indicates the tendency of a and (’ towards their optimal values evidenced by an almost constant variation above .v = 0.5. The change of the axial ratio C./U presents a maximum at approximately the same position as the optimums of u and c. This confirms again the different variation rates of LI and c. According to Kjekshus et al. [IS], it is common view to look at the reduction of C./N from 1.63 as due to metallic bonding along the (,-axis. Consequently. the maxima of (./(I may indicate that FeeSb-Te alloys are less metallic than binary FeSb and Fe-Te. Fig. 2 shows the inverse of the mass magnetic susceptibilities, 1/x,,,) variation with temperature T. The two highest iron compositions x,+ = 0.54 and 0.525 have magnetic field dependent susceptibilities. We believe, this is due to minor magnetic oxides impurities undetected by X-ray diffraction. These
I
Composition
and lattice
parameters
of Fe-Sb-Te
alloys
(‘(A,
C./L/
V(2)
I - ((C~/U)/(L~/~I),‘,)
4.089
5.147
1.259
74.53
0.228
I
3.070
5.
I.273
74.3 I
0.2 I9
0.2
4.050
5.209
I .286
73.99
0.21
4.043
5.219
1.291
73.88
0.208
.x-r.<
y = +J(
0.54
0
0.525 0.51
0.503
0.25
x.,
r + XSh)
II
(.A)
I80
0.49
0.33
4.033
5.255
I.301
73.02
0.201
0.465
0.5
4.022
5.298
I.317
74.22
0. I92
I
A. Rais et al./Materials
263
Letters 33 (1998) 261-264
are responsible for the appearance of effective magnetic moments and consequently for a Curie-Weiss behavior of the mass susceptibility x,, with the temperature T, like: !A &r Xm = 3k,M(T-
2.2 ' 0.0
i 02
I 0.4
0.6
0 8
1.0
Y=XT.I(XTe+XSb)
Fig. 1. (a) Lattice parameters of Fe-Sb-Te alloys versus composition y at 298 K (0, present work; 0, interpolation from Ref. [3]) parameter a (m present work: 0 interpolation from Ref. [3]) parameter c. (b) Axial ratio c/a and cell volume V of Fe-Sb-Te alloys versus composition y at 298 K. (0, present work; 0, Ref. [3]) axial ration c/a (W , present work: 0, Ref. [3]) cell volume V. Note: the full lines connecting the points in (a) and (b), are only an eyeguide. (c) Effective paramagnetic moments petr versus tellurium atomic fraction y. The curve is the fitted theoretical model
were extrapolated to infinite field (l/H + 0) in order to keep the paramagnetic contribution only. The other compositions were field independent. Deviations from linearity above 4.50 K is related to the decomposition of the phase which was reported to occur at 420 K in Fe , +,Te [13]. However, at low temperature deviations are due to transitions to the ordered magnetic state as mentioned above. Because of these reasons, the temperature middle range linearity indicates a paramagnetic character at all compositions. In paramagnetic alloys, the partially filled shells
L9,)
The characteristic parameters are the effective magnetic moment pcff in Bohr magneton per molecular formula units, the paramagnetic Curie temperature 13, and the molar mass M. The other quantities have their usual meaning. The current method to fit the above model is by plotting l/x,,, versus T. Then, providing that the variation is linear, one can extract /_~,rrfrom the slope and 8, from the intersection with the temperature axis. Table 2 shows the results. Interpolation of the data of Richter et al. [3] gives pL,rf= 3pa for binary Fe,,,,,Sb. They also reported the same 0, = -20 K for three compositions of Fe ,+XSb, x = 0.13, 0.22 and 0.3. We believe that these slight disagreements are related to a different thermal treatment of the samples which in view of the structural changes in the system might be of special importance. Fig. l(c) shows the variation of /_~,rr with tellurium atomic fraction y. It is remarkable that the successive substitution of Sb by Te yields an anomaly in p,rr similar to the lattice parameters. This leads us 7,
I
21
IL
OC 0
100
200
Fig. 2. Inverse mass magnetic versus temperature.
400
300 T(K)
500
600
-
susceptibility
of Fe-Sb-Te
alloys
264
A. Rais et al. / Mnteria1.s Letters 33 C19081 261-264
Table 2 Effective magnetic moments and paramagnetic of Fe-Sb-Te alloys XFc
?
&tt
0.54 0.525 0.51 0.503 0.49 0.465
0
2.72 2.60 2.53 2.s2 2.45 2.35
1 0.2 0.25 0.33 0.5
( CLa)
Curie temperatures
‘& (K)(FS) 30 70 65 55 50 53
to believe that structural change and hence crystal field effects are to some extent behind the change in the effective magnetic moments. In consequence, it is relevant to calculate the magnetic moments pre, psh and pLrc per atom Fe, Sb and Te respectively, assuming a p,,.,. model of additivity like: &,‘r = XSh .
,-%b
+
XTe
. ~Tc
+
XFe
. PFe
3
where the atomic concentrations _rFer _~s,, and xTz are related by: xre + us,, + xTe = 1. An acceptable fit was obtained on our six experimental values of pctf using the Simplex numerical method of minimization of the squared residuals sum. The results are ps,, = 0.3~.,, pTe = 0.4~~ and tiFc = 4.7~~. Using these parameters, the theoretical curve of p.,rr against y has been plotted and is shown in Fig. I(c). Since we are unaware of the type of bonding between the atoms, we may interpret the order of magnitude of these values as indicating a prevailing ionic over a metallic character consistent with our previous deduction from the (./(I maxima. In this respect, it appears that the iron magnetic moment is closer to the high spin state Fe’+ value of 4.9~~ rather than the high spin state Fe” value of 5.92 pa suggesting that the predominant ionic state of iron which does not necessarily exclude the other. Furthermore, we may say that crystal field effects mentioned above are responsible for the high spin state Fe’+ and their degree of action may explain the lower value obtained.
4. Conclusions (I) The variations NiAs-type Fe-Sb-Te
of the lattice parameters in alloys when antimony is sub-
stituted by tellurium show an optimal point in the tellurium rich side. (2) In the paramagnetic phase, the variation of the effective magnetic moments per formula unit shows also a minimum in the tellurium rich side. (3) A theoretical model of additive moments of the different atomic species suggests that iron ionic states are closer to Fe’+ than Fe3+. This interpretation of the magnetism in Fe-Sb-Te alloys does not exclude the metallic character or even an interplay of ionic and metallic bonds. In the light of the observed trends, we would propose complementary conductivity and Hall effect measurements on well defined samples in order to investigate the electronic properties of this system. Furthermore, a Mijssbauer spectroscopical study of these alloys will certainly bring to bear the FeZf/Fe3+ ratios and eventually the cationic distribution.
Acknowledgements We would like to express our thanks to our colleagues Dr. A. Hussein and Dr. M. Elzain in the College of Science of SQU who contributed to the present work.
References [I] J. Maier, E. Wachtel, 2. Metallkunde 6 (I 972) 41 I. [2] A.T. Howe, P. Coffin, B.E.F. Fender, J. Phys. C 9 (3) (1976) L6 I -L64. [3] F.W. Richter. K. Schmidt, Z. Naturforsch. 30a (1975) 16211626. [4] F.W. Richter, K. Schmidt, Int. J. Magnetism 5 (1973) 283. [5] J. Nosselt. U. Sondermann, Int. J. Magnetism 5 (1973) 277. [6] N.V. Ageev, E.S. Makarov. Izvest. Akad. 87-98 (1943). [7] K.L. Komarek, P. Terzieff, Mh. Chem. 106 (1975) 145. [8] P. Terzieff. Mh. Chem. 109 (1978) 567. [9] P. Terzieff. Physica B 103 (1981) 158. [IO] K. Reddy, S. Chetty, Phys. Status Solidi (a) 37 (1976) 687. [I I] V. Fano, I. Ortalli, Phys. Status Solidi (a) IO (1972) Kl21. [I21 I. Ortalli, V. Fano. P. Gibart, Phys. Status Solidi (a) 15 (1973) K45. [I 31 H. Ipser. K.L. Komarek. H. Mikler, Mh. Chem. 105 (1974) 1322. [14] P. Ter&ff, Solid State Commun. 50 (1983) 15 I. [I51 A. Kjekshus. W. Pearson, Prog. Sol. St. Chem. I (1964) 83.
1998
Materials Letters 33 (1998) 261-264
ELSEVIER
Lattice parameters and magnetic properties of F-Sb-Te with nickel arsenide structure A. Rais a,*, P. Terzieff a Phwics
Department. b Institute
b, A.A. Yousif a, A.M. Gismelseed
College of Science, Sultan Qaboos lJnirersi@,
P.O. Box 36, Alkhod,
of Inorganic
Vienna, Austria
Received
Chemistp,
Uniwrrit.v
10 April 1997; accepted
of Vienna,
alloys a
Oman
15 April 1997
Abstract Single
phase
Fe-Sb-Te
alloys
with NiAs-type
structure
have been
PACS: 75.30.-m;
Keywords:
75.50.-y
Fe-Sb-Te
alloys; NiAs-type
structure;
Lattice parameters;
1. Introduction The Fe,,,,,Sb and Fe ,,,osTe binary phases have an NiAs-type structure which is basically a HCP matrix where iron atoms occupy the octahedral and bipyramidal interstices [ 1,2]. The deviations from ideal stoichiometry arise because vacant iron sites give rise to wide ranges of stability. The magnetism of Sb has been investigated by several workers E$j using different techniques. Magnetic susceptibility measurements [5] and MBssbauer spectroscopy [3] for 0.13 < x < 0.33 showed that the alloys are antiferromagnetic below a Neel temperature of 1 15
* Corresponding
in the composition range from Fe, ,73Sb to measurements have been taken on these alloys in a linear variation with the alloy composition in the effective magnetic moments extracted from the approximately the same composition. These are atomic species. 0 1998 Elsevier Science B.V.
prepared
Fe ,.,osTe and characterized by X-ray diffraction. Magnetic susceptibility the temperature range from 77 up to 500 K. The lattice parameters show Sb-rich side but an anomalous change for the binary Fe ,,,osTe. The susceptibility variations with temperature show a similar anomaly at discussed in terms of a model of additive magnetic moments of different
author. Fax: + 966-968-5 13436.
00167-577X/98/$19.00 PII 80167-577X(97)001
Magnetic
susceptibility;
Effective magnetic
moments
K varying smoothly with X. The magnetic behavior of NiAs-type Fe, _ ,,Te system suggested antiferromagnetic ordering as reported in previous papers [7-91. However, this has been confirmed by neutron diffraction and Miissbauer spectroscopy only below 10 K [lo- 121. In the composition range 0.29 < x < 0.45, the magnetic susceptibility temperature dependence of these alloys indicated two magnetically different states at high-temperature where the Ni-As phase is stable and the quenched Fe, _ lTe [8]. Owing to the mutual solubility of the binary phases, it is possible to study further the magnetic studies to ternary alloys at concentrations varying between ,,,osTe where the preparation is Fe ,.&b and Fe technically feasible.
0 1998 Elsevier Science B.V. All rights reserved 18-3
2. Experimental The alloys were prepared by direct reaction of the pure elements using Fe sheet (99.9%, Ferrovac E, Vacuum Metals Corporation, Syracuse), and lumps of antimony and tellurium (99.99%, Asarco. New York). The pre-reacted ingots were crushed and homogenised under vacuum (0.01 Pa) at suitable temperatures for a period of 2 weeks. The samples were then annealed at 900 K for 5 days before quenching. The phase purity and structures of the alloys were determined by X-ray diffraction taken using a 57.3 mm Debye-Sherrer camera and Co K,, radiation. The magnetic susceptibility measurements were performed using a Faraday analytical microbalance of 1 Fg precision. An electromagnet with specially shaped poles for constant field gradient, produced field strengths ranging from 3 up to 6 kOe. The magnet calibration was done with Mohr’s salt having a susceptibility of 32.32 X IO-” emu g ’ at 20°C. During the experiment, the sample was contained in a quartz bucket having a temperature independent diamagnetism over a wide range which could be subtracted from the measured magnetic force. An Oxford liquid nitrogen cryostat provided with a heater enabled scanning the temperatures between 77 and 500 K.
3. Results and discussion Different alloys with compositions varying from Fe I ,db ,,,oSTe have been prepared so as to to Fe keep the hexagonal (NiAs-type) structure when antimony is substituted by tellurium [ 131. The X-ray data show that all compositions have NiAs-type structure after quenching. The data analysis enabled the determination of the lattice parameTable
ters. Table I shows the results which consist of the dimensions and the volume of the unit cell together with the axial ratio C/N and the factor I (c/d/( c/a>,, which stands for the reduction in ~/LI from the ideal value (c/n>,, = 1.63. The composition of the alloys needs to be expressed in terms of iron concentration xre and tellurium atomic fraction y = xrJ( xrc + .xsb). Fig. l(a) and (b) show the lattice parameters variations with composition. Our values are in good agreement with the interpolated values of Richter et al. [3]. The anomalous behavior of a and (’ with x is not unique but has been seen in other NiAs-type ternary alloys like Fe-Co-Te [ 141. The linear change of LI and c’ can be accounted by the smaller size of Sb atoms when substituted by Te atoms. Further replacement leads to optimal values of n and c, at a composition F between 0.5 and I. The decrease of the unit cell volume V suggests that the decrease of a is faster than the increase of c. Moreover. the minima of V indicates the tendency of a and (’ towards their optimal values evidenced by an almost constant variation above .v = 0.5. The change of the axial ratio C./U presents a maximum at approximately the same position as the optimums of u and c. This confirms again the different variation rates of LI and c. According to Kjekshus et al. [IS], it is common view to look at the reduction of C./N from 1.63 as due to metallic bonding along the (,-axis. Consequently. the maxima of (./(I may indicate that FeeSb-Te alloys are less metallic than binary FeSb and Fe-Te. Fig. 2 shows the inverse of the mass magnetic susceptibilities, 1/x,,,) variation with temperature T. The two highest iron compositions x,+ = 0.54 and 0.525 have magnetic field dependent susceptibilities. We believe, this is due to minor magnetic oxides impurities undetected by X-ray diffraction. These
I
Composition
and lattice
parameters
of Fe-Sb-Te
alloys
(‘(A,
C./L/
V(2)
I - ((C~/U)/(L~/~I),‘,)
4.089
5.147
1.259
74.53
0.228
I
3.070
5.
I.273
74.3 I
0.2 I9
0.2
4.050
5.209
I .286
73.99
0.21
4.043
5.219
1.291
73.88
0.208
.x-r.<
y = +J(
0.54
0
0.525 0.51
0.503
0.25
x.,
r + XSh)
II
(.A)
I80
0.49
0.33
4.033
5.255
I.301
73.02
0.201
0.465
0.5
4.022
5.298
I.317
74.22
0. I92
I
A. Rais et al./Materials
263
Letters 33 (1998) 261-264
are responsible for the appearance of effective magnetic moments and consequently for a Curie-Weiss behavior of the mass susceptibility x,, with the temperature T, like: !A &r Xm = 3k,M(T-
2.2 ' 0.0
i 02
I 0.4
0.6
0 8
1.0
Y=XT.I(XTe+XSb)
Fig. 1. (a) Lattice parameters of Fe-Sb-Te alloys versus composition y at 298 K (0, present work; 0, interpolation from Ref. [3]) parameter a (m present work: 0 interpolation from Ref. [3]) parameter c. (b) Axial ratio c/a and cell volume V of Fe-Sb-Te alloys versus composition y at 298 K. (0, present work; 0, Ref. [3]) axial ration c/a (W , present work: 0, Ref. [3]) cell volume V. Note: the full lines connecting the points in (a) and (b), are only an eyeguide. (c) Effective paramagnetic moments petr versus tellurium atomic fraction y. The curve is the fitted theoretical model
were extrapolated to infinite field (l/H + 0) in order to keep the paramagnetic contribution only. The other compositions were field independent. Deviations from linearity above 4.50 K is related to the decomposition of the phase which was reported to occur at 420 K in Fe , +,Te [13]. However, at low temperature deviations are due to transitions to the ordered magnetic state as mentioned above. Because of these reasons, the temperature middle range linearity indicates a paramagnetic character at all compositions. In paramagnetic alloys, the partially filled shells
L9,)
The characteristic parameters are the effective magnetic moment pcff in Bohr magneton per molecular formula units, the paramagnetic Curie temperature 13, and the molar mass M. The other quantities have their usual meaning. The current method to fit the above model is by plotting l/x,,, versus T. Then, providing that the variation is linear, one can extract /_~,rrfrom the slope and 8, from the intersection with the temperature axis. Table 2 shows the results. Interpolation of the data of Richter et al. [3] gives pL,rf= 3pa for binary Fe,,,,,Sb. They also reported the same 0, = -20 K for three compositions of Fe ,+XSb, x = 0.13, 0.22 and 0.3. We believe that these slight disagreements are related to a different thermal treatment of the samples which in view of the structural changes in the system might be of special importance. Fig. l(c) shows the variation of /_~,rr with tellurium atomic fraction y. It is remarkable that the successive substitution of Sb by Te yields an anomaly in p,rr similar to the lattice parameters. This leads us 7,
I
21
IL
OC 0
100
200
Fig. 2. Inverse mass magnetic versus temperature.
400
300 T(K)
500
600
-
susceptibility
of Fe-Sb-Te
alloys
264
A. Rais et al. / Mnteria1.s Letters 33 C19081 261-264
Table 2 Effective magnetic moments and paramagnetic of Fe-Sb-Te alloys XFc
?
&tt
0.54 0.525 0.51 0.503 0.49 0.465
0
2.72 2.60 2.53 2.s2 2.45 2.35
1 0.2 0.25 0.33 0.5
( CLa)
Curie temperatures
‘& (K)(FS) 30 70 65 55 50 53
to believe that structural change and hence crystal field effects are to some extent behind the change in the effective magnetic moments. In consequence, it is relevant to calculate the magnetic moments pre, psh and pLrc per atom Fe, Sb and Te respectively, assuming a p,,.,. model of additivity like: &,‘r = XSh .
,-%b
+
XTe
. ~Tc
+
XFe
. PFe
3
where the atomic concentrations _rFer _~s,, and xTz are related by: xre + us,, + xTe = 1. An acceptable fit was obtained on our six experimental values of pctf using the Simplex numerical method of minimization of the squared residuals sum. The results are ps,, = 0.3~.,, pTe = 0.4~~ and tiFc = 4.7~~. Using these parameters, the theoretical curve of p.,rr against y has been plotted and is shown in Fig. I(c). Since we are unaware of the type of bonding between the atoms, we may interpret the order of magnitude of these values as indicating a prevailing ionic over a metallic character consistent with our previous deduction from the (./(I maxima. In this respect, it appears that the iron magnetic moment is closer to the high spin state Fe’+ value of 4.9~~ rather than the high spin state Fe” value of 5.92 pa suggesting that the predominant ionic state of iron which does not necessarily exclude the other. Furthermore, we may say that crystal field effects mentioned above are responsible for the high spin state Fe’+ and their degree of action may explain the lower value obtained.
4. Conclusions (I) The variations NiAs-type Fe-Sb-Te
of the lattice parameters in alloys when antimony is sub-
stituted by tellurium show an optimal point in the tellurium rich side. (2) In the paramagnetic phase, the variation of the effective magnetic moments per formula unit shows also a minimum in the tellurium rich side. (3) A theoretical model of additive moments of the different atomic species suggests that iron ionic states are closer to Fe’+ than Fe3+. This interpretation of the magnetism in Fe-Sb-Te alloys does not exclude the metallic character or even an interplay of ionic and metallic bonds. In the light of the observed trends, we would propose complementary conductivity and Hall effect measurements on well defined samples in order to investigate the electronic properties of this system. Furthermore, a Mijssbauer spectroscopical study of these alloys will certainly bring to bear the FeZf/Fe3+ ratios and eventually the cationic distribution.
Acknowledgements We would like to express our thanks to our colleagues Dr. A. Hussein and Dr. M. Elzain in the College of Science of SQU who contributed to the present work.
References [I] J. Maier, E. Wachtel, 2. Metallkunde 6 (I 972) 41 I. [2] A.T. Howe, P. Coffin, B.E.F. Fender, J. Phys. C 9 (3) (1976) L6 I -L64. [3] F.W. Richter. K. Schmidt, Z. Naturforsch. 30a (1975) 16211626. [4] F.W. Richter, K. Schmidt, Int. J. Magnetism 5 (1973) 283. [5] J. Nosselt. U. Sondermann, Int. J. Magnetism 5 (1973) 277. [6] N.V. Ageev, E.S. Makarov. Izvest. Akad. 87-98 (1943). [7] K.L. Komarek, P. Terzieff, Mh. Chem. 106 (1975) 145. [8] P. Terzieff. Mh. Chem. 109 (1978) 567. [9] P. Terzieff. Physica B 103 (1981) 158. [IO] K. Reddy, S. Chetty, Phys. Status Solidi (a) 37 (1976) 687. [I I] V. Fano, I. Ortalli, Phys. Status Solidi (a) IO (1972) Kl21. [I21 I. Ortalli, V. Fano. P. Gibart, Phys. Status Solidi (a) 15 (1973) K45. [I 31 H. Ipser. K.L. Komarek. H. Mikler, Mh. Chem. 105 (1974) 1322. [14] P. Ter&ff, Solid State Commun. 50 (1983) 15 I. [I51 A. Kjekshus. W. Pearson, Prog. Sol. St. Chem. I (1964) 83.