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Mössbauer study of Fe2O3(Al2O3)x(CuO)1-x system
Solid State Communications, Printed in Great Britain.
Vol.
WBAUER
74,
No.
1,
pp.
l-4,
1990.
0038-1098/90$3.00+.00 Pergamon Press plc
STUDY OF FerOs-(A1aOs)x-(CuO)l-x
SYSTEM
Sung Ho Lee.Kwang Pyo Chae.Young Bae Lee and Kl Seek Oh Department
of Physios.
(Received
Ron-Kuk Unlverslty.
by S. Aaelinckx
Seoul
- January 6.
133-701,
Korea
1990)
The FesOs-(A1sOs)r-(CuO)l-I system (0.0~~~0.6) has been Investigated in the range of O.OrxrO.8 by l eans of X-ray dlffractometw and H&sbauer spectrosoopy. The structure of the system Is a oublo splnel type although It Is strongly nonstolohioaetrlc in the entire composition range. A pair of well defined Zeeaan splittings froa Fe3* Ions at A- and B-sites for x=0.0. and three Zeeaan lines from Fe3+ ions at A- and B-sites and Fez+ lons at B-sites for x ranging from 0.2 to 0.8 have been observed at room temperature. The observed hyperflne fields and Neel teaperatures could be explalned on the lx&s of the superexchange and supertransferred hyperflne interactions.
1. INTRODUCTION
samples were obtained at room temperature with Cu-Ka radiation (A =l.5418ri!. Miissbauer spe(:tra were obtained with a conventional Massbauer spectrometer of the eler:tromechanlcal type \;ith a 57Co source (10mCi) in a palladium matrix.
The spine1 system CuFezOr exists in tetragonal in cubic form. A quenched sample has a and/or cubic spine1 structure, 75% of Cu2+ ions occupies B-sites, however this is not enough to cause a bulk of mixed copper ferrites distortionlll. The study Nl-Cu[41, shovs like Ge-CuCZl, Zn-Cu[Jl, distributions and magnetic interesting cat ion properties. The preparation of such ferrite systems is commonly carried out maintaining the cation-anion number During ratio 3:4 ABz04. the in investigation of magnetic properties of the nonstoichiometric copper oxide system we were able splnel-type solid solution which to synthesize a deviates from the stolchiometry of the strongly prototype spinet and is presumably ferrimagnetic. purpose of the present study is to prepare The nonstoichlometric oxide system, such a Fez03-(A1z03)x-(Cu0)I-x and to investigate the crystallographic and magnetic properties by varying Al and Cu ion concentrations by means of X-ray diffraction and Miissbauer spectroscopy.
3. RESULTSAND DISCUSSION X-ray diffraction patterns show that all the samples have been crystal lized as shown in Fig. 1. The structure of the samples, which shows the presence of similar crystalline phases, changes from the fee structure to the SC structure in the intervening region of x=0.2. The lattice constants have been found with the help of the Nelson-Riley function, and they decrease with increasing A1203 content as shown in Fig.2. This may result from the substitution of larger Cu2* ions for smaller .\I”+ ions, Massbauer spectra were obtained at various absorber temperatures. At room temperature, the Hijssbauer spectra for the whole composition range exhibit well defined Zeeman patterns as shown in Fig.3 and Fig.4. These spectra were analyzed by a computer program based on a least square fitting method with the Lorentzian function. The solid line through the data points is the result of the computer fitting. spectrum for x=0.0 at room temperature The consists of two Zeeman spl ittlngs due to the Fe3+ ions at A- and B-sites. ,411 the samples through to 0.8 exhibit more complex Zeeman x=0.2 splittings. These Zeenan lines can be fitted as the superposition of three sextets due to the Fez+ ions at A- and B-sites and the Fe2+ ions at B-sites. The weak appearance of Fe2+ ions at B-sites for 0.24x50.8 samples can be interpreted as follows. (1) The At3+ ion forms a stable Ne-core in such a compound like this and behaves diamagnetically, whereas the Jd-orbital of Fe3+ ions is not fully occupied by electrons. As a result, the presence of diamagnetic A13+ ions at B-sites would considerably hinder the electron hopping process between the B-sites. and so a fraction of Fe3* ions in B-sites
2. EXPERIMENTAL The samples of x=0.0, 0.2, 0.4, 0.6 and 0.8 in were prepared by a direct Fe203-~AIz03~x-~CuO~i-x A1203 and CuO powders reaction method. a-FenOs, were al I of 99.99% purity. After drying the a-Fez03 and A1203 powders at 200°C for 2 hours, the three in the desired powders were thoroughly mixed To increase the reaction rate, the compositions. mixtures were pressed into the form of pellet using a hydraulic press at 6tons/cm2. These pellets were sealed into evacuated quartz tubes, heated to the temperature of 1100 ‘C for 48 hours and then quenched in liquid nitrogen. In order to obtain a homogeneous specimen, it was necessary to grind the samples after firing. This procedure was repeated tvo times and then the samples were used for X-ray analysis and Hijssbauer study in powder form. Y-ray diffraction patterns of the powder 1
MOSSBAUERSTUDY OF Fe203-(A1203)x-
(CuO),_x
I”““““’
-10 -0
Fig. 1. samples
02
Fig.2. The variation samples 0.05x50.8.
patterns
-2
0
lattice
Cki3
parameters
2
4
6
Vol.
74,
6
l0
No.
(mm/s)
for Fig.3. Mossbauer spectra at room temperature.
O.lt X of
-4
VELOCITY
X-ray diffraction O.O
OIJ
-6
SYSTEM
a8
for
is compelled to transfer to a Fez+ state or to enigrate to A-sites. (2) The random cation distribution and/or a slight distortion from the regular spine1 structure of A6204 seens to change a fraction of Fe ions from Fe3+ states to Fez+ states in B-sites. Rosenberg and Franke [51 have satisfactorily distribution of explained the finite hyperf ine fields as a number of Fez+ possibilities local FeJ+ for the and
for
samples
x=0.0,
0.2
populations. It could be explained as a result of substitutional disorder and fast local averaging of the spatially fluctuating electron density. Fig, 5 shows the dependence of the magnetic hyperfine fields (MHF) on the composition. It is evident that HA of Fe3+ slightly increases and He of Fe3+ decreases with increasing x, and the Ha of Fe2+ slightly increases. Similar variations of HA and HB were observed in Ni-Zn ferrite system161 and Mn-Zn system[‘ll. This variation has been basis of the explained on the increment of covalence of Fe3+-02- bonds and/or the contribution of the supertransferred hyperfine interactions at A- and B-sites of Fe ions. We also observe similar behaviors of the Miissbauer parameters. Thus we believe that a spin canted structure should be present in our system. The variation of the hyperfine field with Al system can be explained concentration in our qualitatively as follows: in the quenched copper ferrite with Cu2+ ions(75Xl on B-sites, the site preference leads predominantly to an inverse spine1 structure, and it is well known that Ala+ ions have a strong B-site preference [8.9l.The A13+ ions substituted for Cu2+ ions will cause the migration from B- to A-sites. This can be of Fe3+ ions verified with the help of the intensity ratios. In most magnetically ordered spine1 phases, the Nrel ordering is determined mainly by the strong the and antiferromagnetic A-B interactions, contribution of B-B interaction to this is very weak. However, in our case, it is necessary to take not only the A-B superexchange but also the B-B into interactions supertransferred hyperf ine
1
Vol.
74, No. 1
MijSSBAUER STUDY OF Fe203-(AlZOS)x-
z
(CuO),_x
SYSTEM
470
0
,Y
I
HB(Fe3+) ‘\c- --a---+
450
I 0.0
Fig.5. field
I
I
-10 -8
I
-8
1
I
1
I
I
I
I
-2
0
2
4
8
8
10
1
-4
VELOCITY Fig.4. Mijssbauer spectra for 0.6, 0.6 at room temperature.
I
0.2
I 0.4 X
I 0.8
I 0.8
The variation of magnetic hyperfine for samples O.OsxsO.8 at room temperature.
(mm/s) samples
x=0.4,
As a result of these, HA increases with account. increasing x, whereas He decreases with x. Recently Baldha and Kulkarni Cl01 have given a satisfactory explanation for the variations of the with Ge concentration in hyperf ine fields CexCui-xFes04 in terms of the A-B and B-B supertransferred hyperfine interactions, and this system also has a spin canted structure similar to that of Fe-ZnCll] and Cu-Zn ferrites 1121. The isomer shift and quadrupole splitting at Aand B-sit.es show no significant variation with increasing x. In general, the A-site in the ideal structure has a cubic Td symmetry and spine1 therefore gives no electric field gradient at the but the B-site has a trigonal point cation, anticipates a large electric symmetry and one field gradient. However, in the systems having wide solid solution or nonstoichiometric ranges of the Mossbauer spectrum is always composition, accompanied by nonvanishing QS due to the slight randomness of environments of Fe ions. Fig. 6 shows the magnetic ordering temperatures as a function of composition. The magnetic ordering
FIg.6. The variation of samples 0.04xso.a.
Neel temperature
for
temperature was measured from the temperature dependence of the MHF. The temperature dependence of magnetization usually follows a Brillouin function. The magnetization and hence the internal field decrease with increasing temperature and become zero at the Curie or Nael temperature. The Neel temperature has been known tv be proportional t.o the strength of the exchange
4
M&5SBAUER STUDY OF Fe203-(h1203)x-
interaction, Gilleo Cl31 proposed the superexchange interaction of that the Neel temperature depends the number of Fe3*-0-Fe3+ linkages. the Neel temperature increases with the basis of explained on
in hls study on various oxides primarily upon In our system x. This can be increment of
(CuO) ,_x
superexchange the variation
Vol.
SYSTM
interaction, which is of the HHF at A-sites
74,
No.
also related to as shown Fig.5.
AcknowledgementThis work has been the Basic Sciences Promotion Program, of Education, Korea. 1989.
supported by the Ministry
REFERENCES 1. T. Hiyadai. S. Miyahara and Y. Matsuo, J. Phys. Sot. Japan, 20. 980 (1965). Kulkarni 2. R.G. and G.J. Baldha, Solid stat commun. 17. 843(1982). 3. R.G. Kulkarni and V.U. Patil, J. Hater. Sci. 17. 843(1982). 4. A. A. Chani, A. I. Etyhh and A.A. Mohamed, Ferrites, Proc. Int. Conf., 216. Sept. 1980, Japan. 5. M. Rosenberg, H. Franke, Ferrites. Proc. Int. 1980, Japan. Conf . , 146. Sept. 6. L.K. Leung. B.J. Evans and A.H. Morrish, Phys. Rev. BB, 29(1973). 7. A.H. Morrish and P.E.Clark. Phys. Rev. Bll. 278(1975).
8.
S.K. Kulshrestha and G. Ritter, J. Mater. Sci. 20, 821(1985). 9. A. Navrotsky and O.J. Kleppa. J. Inorg. Nut. Chem. 29, 2701(19671. Baldha and R.C. Kulkarni. Solid State 10. C.A. Comaun. 49. 169(1984). and R. G. 11. C. M. Srivastava. S. N. Shrlngi Srivastava, Phys. Rev. Bl4. 2041(1976). 12. V. U. Patil and R. C. Kulkarni, Solid State Commun. 31, 551(1979). 13. M.A. Gilleo, Phys. Rev. 109, 777(1958).
1
Vol.
WBAUER
74,
No.
1,
pp.
l-4,
1990.
0038-1098/90$3.00+.00 Pergamon Press plc
STUDY OF FerOs-(A1aOs)x-(CuO)l-x
SYSTEM
Sung Ho Lee.Kwang Pyo Chae.Young Bae Lee and Kl Seek Oh Department
of Physios.
(Received
Ron-Kuk Unlverslty.
by S. Aaelinckx
Seoul
- January 6.
133-701,
Korea
1990)
The FesOs-(A1sOs)r-(CuO)l-I system (0.0~~~0.6) has been Investigated in the range of O.OrxrO.8 by l eans of X-ray dlffractometw and H&sbauer spectrosoopy. The structure of the system Is a oublo splnel type although It Is strongly nonstolohioaetrlc in the entire composition range. A pair of well defined Zeeaan splittings froa Fe3* Ions at A- and B-sites for x=0.0. and three Zeeaan lines from Fe3+ ions at A- and B-sites and Fez+ lons at B-sites for x ranging from 0.2 to 0.8 have been observed at room temperature. The observed hyperflne fields and Neel teaperatures could be explalned on the lx&s of the superexchange and supertransferred hyperflne interactions.
1. INTRODUCTION
samples were obtained at room temperature with Cu-Ka radiation (A =l.5418ri!. Miissbauer spe(:tra were obtained with a conventional Massbauer spectrometer of the eler:tromechanlcal type \;ith a 57Co source (10mCi) in a palladium matrix.
The spine1 system CuFezOr exists in tetragonal in cubic form. A quenched sample has a and/or cubic spine1 structure, 75% of Cu2+ ions occupies B-sites, however this is not enough to cause a bulk of mixed copper ferrites distortionlll. The study Nl-Cu[41, shovs like Ge-CuCZl, Zn-Cu[Jl, distributions and magnetic interesting cat ion properties. The preparation of such ferrite systems is commonly carried out maintaining the cation-anion number During ratio 3:4 ABz04. the in investigation of magnetic properties of the nonstoichiometric copper oxide system we were able splnel-type solid solution which to synthesize a deviates from the stolchiometry of the strongly prototype spinet and is presumably ferrimagnetic. purpose of the present study is to prepare The nonstoichlometric oxide system, such a Fez03-(A1z03)x-(Cu0)I-x and to investigate the crystallographic and magnetic properties by varying Al and Cu ion concentrations by means of X-ray diffraction and Miissbauer spectroscopy.
3. RESULTSAND DISCUSSION X-ray diffraction patterns show that all the samples have been crystal lized as shown in Fig. 1. The structure of the samples, which shows the presence of similar crystalline phases, changes from the fee structure to the SC structure in the intervening region of x=0.2. The lattice constants have been found with the help of the Nelson-Riley function, and they decrease with increasing A1203 content as shown in Fig.2. This may result from the substitution of larger Cu2* ions for smaller .\I”+ ions, Massbauer spectra were obtained at various absorber temperatures. At room temperature, the Hijssbauer spectra for the whole composition range exhibit well defined Zeeman patterns as shown in Fig.3 and Fig.4. These spectra were analyzed by a computer program based on a least square fitting method with the Lorentzian function. The solid line through the data points is the result of the computer fitting. spectrum for x=0.0 at room temperature The consists of two Zeeman spl ittlngs due to the Fe3+ ions at A- and B-sites. ,411 the samples through to 0.8 exhibit more complex Zeeman x=0.2 splittings. These Zeenan lines can be fitted as the superposition of three sextets due to the Fez+ ions at A- and B-sites and the Fe2+ ions at B-sites. The weak appearance of Fe2+ ions at B-sites for 0.24x50.8 samples can be interpreted as follows. (1) The At3+ ion forms a stable Ne-core in such a compound like this and behaves diamagnetically, whereas the Jd-orbital of Fe3+ ions is not fully occupied by electrons. As a result, the presence of diamagnetic A13+ ions at B-sites would considerably hinder the electron hopping process between the B-sites. and so a fraction of Fe3* ions in B-sites
2. EXPERIMENTAL The samples of x=0.0, 0.2, 0.4, 0.6 and 0.8 in were prepared by a direct Fe203-~AIz03~x-~CuO~i-x A1203 and CuO powders reaction method. a-FenOs, were al I of 99.99% purity. After drying the a-Fez03 and A1203 powders at 200°C for 2 hours, the three in the desired powders were thoroughly mixed To increase the reaction rate, the compositions. mixtures were pressed into the form of pellet using a hydraulic press at 6tons/cm2. These pellets were sealed into evacuated quartz tubes, heated to the temperature of 1100 ‘C for 48 hours and then quenched in liquid nitrogen. In order to obtain a homogeneous specimen, it was necessary to grind the samples after firing. This procedure was repeated tvo times and then the samples were used for X-ray analysis and Hijssbauer study in powder form. Y-ray diffraction patterns of the powder 1
MOSSBAUERSTUDY OF Fe203-(A1203)x-
(CuO),_x
I”““““’
-10 -0
Fig. 1. samples
02
Fig.2. The variation samples 0.05x50.8.
patterns
-2
0
lattice
Cki3
parameters
2
4
6
Vol.
74,
6
l0
No.
(mm/s)
for Fig.3. Mossbauer spectra at room temperature.
O.lt X of
-4
VELOCITY
X-ray diffraction O.O
OIJ
-6
SYSTEM
a8
for
is compelled to transfer to a Fez+ state or to enigrate to A-sites. (2) The random cation distribution and/or a slight distortion from the regular spine1 structure of A6204 seens to change a fraction of Fe ions from Fe3+ states to Fez+ states in B-sites. Rosenberg and Franke [51 have satisfactorily distribution of explained the finite hyperf ine fields as a number of Fez+ possibilities local FeJ+ for the and
for
samples
x=0.0,
0.2
populations. It could be explained as a result of substitutional disorder and fast local averaging of the spatially fluctuating electron density. Fig, 5 shows the dependence of the magnetic hyperfine fields (MHF) on the composition. It is evident that HA of Fe3+ slightly increases and He of Fe3+ decreases with increasing x, and the Ha of Fe2+ slightly increases. Similar variations of HA and HB were observed in Ni-Zn ferrite system161 and Mn-Zn system[‘ll. This variation has been basis of the explained on the increment of covalence of Fe3+-02- bonds and/or the contribution of the supertransferred hyperfine interactions at A- and B-sites of Fe ions. We also observe similar behaviors of the Miissbauer parameters. Thus we believe that a spin canted structure should be present in our system. The variation of the hyperfine field with Al system can be explained concentration in our qualitatively as follows: in the quenched copper ferrite with Cu2+ ions(75Xl on B-sites, the site preference leads predominantly to an inverse spine1 structure, and it is well known that Ala+ ions have a strong B-site preference [8.9l.The A13+ ions substituted for Cu2+ ions will cause the migration from B- to A-sites. This can be of Fe3+ ions verified with the help of the intensity ratios. In most magnetically ordered spine1 phases, the Nrel ordering is determined mainly by the strong the and antiferromagnetic A-B interactions, contribution of B-B interaction to this is very weak. However, in our case, it is necessary to take not only the A-B superexchange but also the B-B into interactions supertransferred hyperf ine
1
Vol.
74, No. 1
MijSSBAUER STUDY OF Fe203-(AlZOS)x-
z
(CuO),_x
SYSTEM
470
0
,Y
I
HB(Fe3+) ‘\c- --a---+
450
I 0.0
Fig.5. field
I
I
-10 -8
I
-8
1
I
1
I
I
I
I
-2
0
2
4
8
8
10
1
-4
VELOCITY Fig.4. Mijssbauer spectra for 0.6, 0.6 at room temperature.
I
0.2
I 0.4 X
I 0.8
I 0.8
The variation of magnetic hyperfine for samples O.OsxsO.8 at room temperature.
(mm/s) samples
x=0.4,
As a result of these, HA increases with account. increasing x, whereas He decreases with x. Recently Baldha and Kulkarni Cl01 have given a satisfactory explanation for the variations of the with Ge concentration in hyperf ine fields CexCui-xFes04 in terms of the A-B and B-B supertransferred hyperfine interactions, and this system also has a spin canted structure similar to that of Fe-ZnCll] and Cu-Zn ferrites 1121. The isomer shift and quadrupole splitting at Aand B-sit.es show no significant variation with increasing x. In general, the A-site in the ideal structure has a cubic Td symmetry and spine1 therefore gives no electric field gradient at the but the B-site has a trigonal point cation, anticipates a large electric symmetry and one field gradient. However, in the systems having wide solid solution or nonstoichiometric ranges of the Mossbauer spectrum is always composition, accompanied by nonvanishing QS due to the slight randomness of environments of Fe ions. Fig. 6 shows the magnetic ordering temperatures as a function of composition. The magnetic ordering
FIg.6. The variation of samples 0.04xso.a.
Neel temperature
for
temperature was measured from the temperature dependence of the MHF. The temperature dependence of magnetization usually follows a Brillouin function. The magnetization and hence the internal field decrease with increasing temperature and become zero at the Curie or Nael temperature. The Neel temperature has been known tv be proportional t.o the strength of the exchange
4
M&5SBAUER STUDY OF Fe203-(h1203)x-
interaction, Gilleo Cl31 proposed the superexchange interaction of that the Neel temperature depends the number of Fe3*-0-Fe3+ linkages. the Neel temperature increases with the basis of explained on
in hls study on various oxides primarily upon In our system x. This can be increment of
(CuO) ,_x
superexchange the variation
Vol.
SYSTM
interaction, which is of the HHF at A-sites
74,
No.
also related to as shown Fig.5.
AcknowledgementThis work has been the Basic Sciences Promotion Program, of Education, Korea. 1989.
supported by the Ministry
REFERENCES 1. T. Hiyadai. S. Miyahara and Y. Matsuo, J. Phys. Sot. Japan, 20. 980 (1965). Kulkarni 2. R.G. and G.J. Baldha, Solid stat commun. 17. 843(1982). 3. R.G. Kulkarni and V.U. Patil, J. Hater. Sci. 17. 843(1982). 4. A. A. Chani, A. I. Etyhh and A.A. Mohamed, Ferrites, Proc. Int. Conf., 216. Sept. 1980, Japan. 5. M. Rosenberg, H. Franke, Ferrites. Proc. Int. 1980, Japan. Conf . , 146. Sept. 6. L.K. Leung. B.J. Evans and A.H. Morrish, Phys. Rev. BB, 29(1973). 7. A.H. Morrish and P.E.Clark. Phys. Rev. Bll. 278(1975).
8.
S.K. Kulshrestha and G. Ritter, J. Mater. Sci. 20, 821(1985). 9. A. Navrotsky and O.J. Kleppa. J. Inorg. Nut. Chem. 29, 2701(19671. Baldha and R.C. Kulkarni. Solid State 10. C.A. Comaun. 49. 169(1984). and R. G. 11. C. M. Srivastava. S. N. Shrlngi Srivastava, Phys. Rev. Bl4. 2041(1976). 12. V. U. Patil and R. C. Kulkarni, Solid State Commun. 31, 551(1979). 13. M.A. Gilleo, Phys. Rev. 109, 777(1958).
1