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Temperature dependence of the magnetic properties of the rare-earth-transition-metal intermetallic Lu2Fe14C
Journal of Magnetism and Magnetic Materials 96 (1991) 219-222 North-HoIl~d
219
Temperature dependence of the magnetic properties of the rare-earth-transition-metal intermetallic Lu ,Fe,,C Zhang Zhi-dong a*b,X.K. Sun a,b, Zhao Zhi-gang a, Y.C. Chuang a and F.R. de Boer ’ a institute
of Meial Research. Acadgm~a Sinica, Wenhua Road, Shenyang IlOOiS, China ’ ~~ternatio~a~Center for Material Physics, Academia Sinica, Wenhua Road Shenyang I 10015, China ’ Natuurkundig Laboratorium, University of Amsterdam, Vaickenierstraat 65, IO18 XE Amsterdam, Netherlands
Received 29 August 1990; in revised form 16 October 1990
Ma~et~ation curves of the ternary tetragonat compound Lu 2Fe,,C were measured in an extracting-sample magnetometer in the temperature range from 1.5 to 300 K. The temperature dependence of the magnetic properties of Lu ,Fe,,C is discussed.
1. Introduction
Recently, some interesting results of studies focusing on a new series of carbides of the type R,Fe,,C have been reported [l-4]. In a previous report [l], the magnetic properties of the R,Fe,,C compounds were found to be in most respects very similar to those of the correspond~g borides, suggesting that the carbon-based compounds may be explored as starting materials for permanent-magnet purposes. A recent investigation showed that the room-temperature anisotropy field of Nd,Fe,,C is about 100 kOe, which is much larger than that of Nd,Fe,,B [5]. This has urged us to perform a further investigation of the magnetic properties of the R,Fe,,C-type compounds. In the present work, magnetization curves of the ternary tetragonal compound Lu 2Fe& were measured in an extracting-s~ple ma~etometer in the temperature range from 1.5 to 300 K. The temperature dependence of the magnetic properties of Lu 2Fe,,C is discussed.
2. Ex~rimen~i
details
A polycrystalline sample of Lu,Fe,,C was prepared from 99.9% pure starting materials by means
of arc melting in purified argon gas [l]. After arc melting, the ingot was wrapped in Ta-foil, sealed into an evacuated quartz tube and vacuum annealed at 800-900 o C for a period of several weeks. The homogenized sample was verified by means of X-ray diffraction to be approximately single phase with the tetragonal Nd,Fe,,B-type structure [l]. Samples for high-field ma~et~ation measurements were prepared by aligning fine powders at room temperature in a magnetic field of about 1 T and by fixing them in epoxy resin in the shape of cylinders with the long axis either parallel or perpendicular to the alignment direction. The magnetization measurements were carried out in an extracting-sample magnetometer at the Institute of Physics, academia Sinica.
3. Results and discussion Magnetization curves of Lu,Fe,,C were measured in the temperature range between 1.5 and 300 K with the magnetic field applied either parallel or perpendicular to the alignment direction. Figures 1 and 2 show the magnetization curves at 1.5 and 300 K, respectively. The saturation magnetization values, M, represented in fig. 3 have been determined by extrapolation of the magneti-
0304-8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)
Z.-d. Zhong et 01. / RE-TM
220
I
o .*
:
ooze
oooo /I 0
s_slOo--
.
E E;
0
.
.
.
Lu, Fe,,C‘
1501
I
. .
,
@
. l’
E’lOO--
3
50--
Lu2FelLC
l.
--30
0
8
l
I
l
/I
50--
intermetallic
T=1.5K
1 5 --2o$ z
.
00 0
20
60
$ I&e)
Fig. 1. Magnetization curves at 1.5 K of magnetically-aligned Lu2Fe,,C with the magnetic field applied parallel and perpendicular to the alignment direction.
zation as l/B.
data
to infinite
Because
field assuming
that
Lu is non-magnetic,
M varies the
values
for the saturation magnetization correspond to the magnetic moment of the Fe sublattice, p,+, which are also shown in fig. 3. It can be seen that both the saturation magnetization and the magnetic moment of the Fe sublattice decrease slightly with increasing temperature. The value at 300 K of p,+ = 23.8p,/f.u. is about 14% smaller than that at 1.5 K. However, our present value pFr = 27.7pJf.u. obtained at 1.5 K is slightly larger than the previous value, 27.2pL,/f.u., which was derived by extrapolating the magnetization data to zero field. As suggested in ref. [l], it is reasonable
o”
CM
.
0
l
l
l
.
. .
.
0
.
.
O.*.eO
000
.
.
.
LqFe&
.
T-300K
.
I
I
1
20
LO
H(kOe)
, _
60
Fig. 2. Magnetization curves at 300 K of magnetically-aligned Lu2Fe,,C with the magnetic field applied parallel and perpendicular to the alignment direction.
T(K)
Fig. 3. Temperature dependence of the saturation magnetuation and the magnetic moment of the Fe sublattice in Lu ,Fe,,C.
that in the R,Fe,,C compounds the value for the Fe-sublattice magnetization is about 10% higher than in the Lu compound and the Fe-sublattice magnetization is approximately equal to 30~~ per formula unit R,Fe,,C. At 1.5 K. the magnetic moment per Fe atom in Lu2Fe,,C is approximately 1.98~ a, which is slightly smaller than the value of 2.2~~ in Fe metal. As a generally observed phenomenon in R-Fe and Fe-B compounds, with increasing concentration of R or B the Fe moment may decrease through 5d or p electron transfer into the 3d band [6] and 5dP3d or p-d hybridization [7]. The present value for the Fe magnetic moment is also smaller than that reported earlier for Lu,Fe,,B [8]. This may be explained by the larger number of electrons in the outer shell of C, leading to the transfer of more electrons to the 3d band. In the present case, the anisotropy field HA can be estimated from the intersection of the u,, and crI magnetization curves. The values for the anisotropy constant K, were derived from the values for the anisotropy field by means of the expression K, = H,M,/2. The temperature dependences of the anisotropy field HA and the anisotropy constant K, are given in fig. 4. The values of the magnetic anisotropy obtained for Lu,Fe,,C are larger than those for the corresponding boride Lu,Fe,,B. Since Lu is nonmagnetic, it has zero contribution to the magnetocrystalline anisotropy. Therefore, the magnetic anisotropy of Lu,Fe,,C and Lu,Fe,,B only arises from the Fe sublattice.
Z.-d. Zhang et al. / RE-TM
intermetallic LulFe,,C
221
anistropy has been explained partly by taking into account the temperature dependence of c/a [&lo]: K,(T)
0
300 T(K)
Fig. 4. Temperature dependences of the anisotropy and the anisotropy constant K, in Lu,Fe,,C.
field
H,,
This means that the contribution from the Fe sublattice to the magnetocrystalline anisotropy is larger in R,Fe,,C than in R,Fe,,B compounds. The contribution to the magnetic anisotropy arising from the Fe sublattice is usually due to the incompletely quenched orbital angular momentum of the Fe atoms and dipolar interaction between the magnetic moments. The larger number of electrons in the outer shell of C atoms than in B atoms, leads to the transfer of more electrons to the 3d band, resulting in a decrease of the magnetic moment of the Fe atoms. This may lead to a slight decrease in the dipolar anisotropy. Therefore, one may expect that compared with the borides, the slight increase in the magnetic anisotropy of the Fe sublattice may originate from: (1) an increase in the magnetic anisotropy contributed by the orbital moment of the Fe atoms; (2) an increase in the dipolar anisotropy due to the change of lattice parameters; (3) the decrease of saturation magnetization of the carbides. From fig. 4, it can be seen that the anisotropy field of Lu,Fe,,C at 1.5 K is slightly higher than at room temperature. A maximum in the temperature dependence of the anisotropy field is found, whereas no maximum in the temperature dependence of the anisotropy constant is observed. Obviously, the maximum in the temperature dependence of the anisotropy field is less pronounced than that found by various authors for the corresponding boride Lu,Fe,,B [8,9]. The anomalous temperature dependence of the Fe-sublattice
=
K,(O)[~,,(T)/~~,(O)l”[l - ~W,‘].
The disappearance of the anomalous behaviour of K,(T) in Lu,Fe,,C suggests that the change in the crystal-field interactions associated with the magnetovolume anomaly, which occurs in R,Fe,,B compounds below T,,may become less pronounced in Lu,Fe,,C. In dealing with the anomalous temperature dependence of the Fe anisotropy in R,Fe,,B, it has been suggested in ref. [8], that this effect may result from a competition between different temperature dependences of the individual contributions from different Fe sites. It is likely that the effects of such a competition have become less clear in Lu,Fe,,C. On the other hand, our previous investigation has revealed that also in Gd,Fe,,C an anomalous temperature dependence of the Fe anisotropy exists [ll]. It is very likely that the disappearance of the anomalous behaviour in Lu,Fe,,C must be ascribed to the coexistent actions of Lu and C on the magnetocrystalline anisotropy of the Fe sublattice. In conclusion, the saturation magnetization and the magnetic moment per Fe atom of Lu*Fe,,C are slightly smaller than in Lu,Fe,,B, whereas the magnetocrystalline anisotropy of Lu,Fe,,C is found to be larger than in the corresponding boride. The anomalous behaviour in the temperature dependence of the Fe-sublattice anisotropy, as ascribed to the different temperature dependences of the individual contributions from different Fe sites and/or the change of the Fe anisotropy associated with the magnetovolume anomaly, are found to be less pronounced.
Acknowledgements The present work has been carried out within the scientific exchange program between China and The Netherlands and has been partly supported by the Concerted European Action on Magnets (CEAM), the National Natural Sciences Foundation of China and the Magnetism Labora-
222
2. -d. Zhang et ul. / RE
tory of the Institute of Physics, Academia Sinica. The authors greatly appreciate Professor K.H.J. Buschow of the Philips Research Laboratories for providing polycrystalline samples and Professor Fan Shi-yong of the Institute of Physics for help during the magnetization measurements.
References [II F.R. de Boer, Huang Ying-kai, Mooij
and
K.H.J.
Buschow,
Zhang Zhi-dong, J. Magn. Magn.
D.B. de Mat. 72
(1988) 167.
I4 F.R. de Boer, R. Verhoef. Zhang Zhi-dong,
D.B. de Mooij and K.H.J. Buschow, J. Magn. Magn. Mat. 73 (1988) 263. J. [31 K.H.J. Buschow, D.B. de Mooij and C.J.M. Den&en, Less-Common Metals 142 (1988) L13.
TM intermetalltc
Lu, Fe,,C
[4] R. Verhoef, F.R. de Boer. Yang Fuming, Zhang Zhi-dong. B.D. de Mooij and K.H.J. Buschow, J. Magn. Magn. Mat. 80 (1989) 37. [S] Liu Wei. Zhang Zhi-dong, X.K. Sun, Y.C. Chuang. Yang Fuming and F.R. de Boer. Solid State Commun. 76 (1990) 1375. [6] H.R. Kirchmayr and C.A. Poldy. Handbook on the Physics and Chemistry of Rare Earths, eds. K.A. Gschneidner, Jr. and L. Eyring (North-Holland. Amsterdam, 1979) chap. 14. [7] R. Hasegawa and R. Ray, J. Appl. Phys. 49 (1978) 4174. [8] F. Bolzoni, J.P. Gavigan. D. Givord, H.S. Li, 0. Moze and L. Pareti, J. Magn. Magn. Mat. 66 (1987) 158. [9] X.K. Sun, PhD Thesis, Techn. Univ. Vienna (1985). [lo] M.I. Bartashevich and A.V. Andreev, Physica B 162 (1990) 52. [ll] X.C. Kou, X.K. Sun, Y.C. Chuang, T.S. Zhao. R. Grossinger and H.R. Kirchmayr, Solid State Commun. 73 (1990) 87.
219
Temperature dependence of the magnetic properties of the rare-earth-transition-metal intermetallic Lu ,Fe,,C Zhang Zhi-dong a*b,X.K. Sun a,b, Zhao Zhi-gang a, Y.C. Chuang a and F.R. de Boer ’ a institute
of Meial Research. Acadgm~a Sinica, Wenhua Road, Shenyang IlOOiS, China ’ ~~ternatio~a~Center for Material Physics, Academia Sinica, Wenhua Road Shenyang I 10015, China ’ Natuurkundig Laboratorium, University of Amsterdam, Vaickenierstraat 65, IO18 XE Amsterdam, Netherlands
Received 29 August 1990; in revised form 16 October 1990
Ma~et~ation curves of the ternary tetragonat compound Lu 2Fe,,C were measured in an extracting-sample magnetometer in the temperature range from 1.5 to 300 K. The temperature dependence of the magnetic properties of Lu ,Fe,,C is discussed.
1. Introduction
Recently, some interesting results of studies focusing on a new series of carbides of the type R,Fe,,C have been reported [l-4]. In a previous report [l], the magnetic properties of the R,Fe,,C compounds were found to be in most respects very similar to those of the correspond~g borides, suggesting that the carbon-based compounds may be explored as starting materials for permanent-magnet purposes. A recent investigation showed that the room-temperature anisotropy field of Nd,Fe,,C is about 100 kOe, which is much larger than that of Nd,Fe,,B [5]. This has urged us to perform a further investigation of the magnetic properties of the R,Fe,,C-type compounds. In the present work, magnetization curves of the ternary tetragonal compound Lu 2Fe& were measured in an extracting-s~ple ma~etometer in the temperature range from 1.5 to 300 K. The temperature dependence of the magnetic properties of Lu 2Fe,,C is discussed.
2. Ex~rimen~i
details
A polycrystalline sample of Lu,Fe,,C was prepared from 99.9% pure starting materials by means
of arc melting in purified argon gas [l]. After arc melting, the ingot was wrapped in Ta-foil, sealed into an evacuated quartz tube and vacuum annealed at 800-900 o C for a period of several weeks. The homogenized sample was verified by means of X-ray diffraction to be approximately single phase with the tetragonal Nd,Fe,,B-type structure [l]. Samples for high-field ma~et~ation measurements were prepared by aligning fine powders at room temperature in a magnetic field of about 1 T and by fixing them in epoxy resin in the shape of cylinders with the long axis either parallel or perpendicular to the alignment direction. The magnetization measurements were carried out in an extracting-sample magnetometer at the Institute of Physics, academia Sinica.
3. Results and discussion Magnetization curves of Lu,Fe,,C were measured in the temperature range between 1.5 and 300 K with the magnetic field applied either parallel or perpendicular to the alignment direction. Figures 1 and 2 show the magnetization curves at 1.5 and 300 K, respectively. The saturation magnetization values, M, represented in fig. 3 have been determined by extrapolation of the magneti-
0304-8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)
Z.-d. Zhong et 01. / RE-TM
220
I
o .*
:
ooze
oooo /I 0
s_slOo--
.
E E;
0
.
.
.
Lu, Fe,,C‘
1501
I
. .
,
@
. l’
E’lOO--
3
50--
Lu2FelLC
l.
--30
0
8
l
I
l
/I
50--
intermetallic
T=1.5K
1 5 --2o$ z
.
00 0
20
60
$ I&e)
Fig. 1. Magnetization curves at 1.5 K of magnetically-aligned Lu2Fe,,C with the magnetic field applied parallel and perpendicular to the alignment direction.
zation as l/B.
data
to infinite
Because
field assuming
that
Lu is non-magnetic,
M varies the
values
for the saturation magnetization correspond to the magnetic moment of the Fe sublattice, p,+, which are also shown in fig. 3. It can be seen that both the saturation magnetization and the magnetic moment of the Fe sublattice decrease slightly with increasing temperature. The value at 300 K of p,+ = 23.8p,/f.u. is about 14% smaller than that at 1.5 K. However, our present value pFr = 27.7pJf.u. obtained at 1.5 K is slightly larger than the previous value, 27.2pL,/f.u., which was derived by extrapolating the magnetization data to zero field. As suggested in ref. [l], it is reasonable
o”
CM
.
0
l
l
l
.
. .
.
0
.
.
O.*.eO
000
.
.
.
LqFe&
.
T-300K
.
I
I
1
20
LO
H(kOe)
, _
60
Fig. 2. Magnetization curves at 300 K of magnetically-aligned Lu2Fe,,C with the magnetic field applied parallel and perpendicular to the alignment direction.
T(K)
Fig. 3. Temperature dependence of the saturation magnetuation and the magnetic moment of the Fe sublattice in Lu ,Fe,,C.
that in the R,Fe,,C compounds the value for the Fe-sublattice magnetization is about 10% higher than in the Lu compound and the Fe-sublattice magnetization is approximately equal to 30~~ per formula unit R,Fe,,C. At 1.5 K. the magnetic moment per Fe atom in Lu2Fe,,C is approximately 1.98~ a, which is slightly smaller than the value of 2.2~~ in Fe metal. As a generally observed phenomenon in R-Fe and Fe-B compounds, with increasing concentration of R or B the Fe moment may decrease through 5d or p electron transfer into the 3d band [6] and 5dP3d or p-d hybridization [7]. The present value for the Fe magnetic moment is also smaller than that reported earlier for Lu,Fe,,B [8]. This may be explained by the larger number of electrons in the outer shell of C, leading to the transfer of more electrons to the 3d band. In the present case, the anisotropy field HA can be estimated from the intersection of the u,, and crI magnetization curves. The values for the anisotropy constant K, were derived from the values for the anisotropy field by means of the expression K, = H,M,/2. The temperature dependences of the anisotropy field HA and the anisotropy constant K, are given in fig. 4. The values of the magnetic anisotropy obtained for Lu,Fe,,C are larger than those for the corresponding boride Lu,Fe,,B. Since Lu is nonmagnetic, it has zero contribution to the magnetocrystalline anisotropy. Therefore, the magnetic anisotropy of Lu,Fe,,C and Lu,Fe,,B only arises from the Fe sublattice.
Z.-d. Zhang et al. / RE-TM
intermetallic LulFe,,C
221
anistropy has been explained partly by taking into account the temperature dependence of c/a [&lo]: K,(T)
0
300 T(K)
Fig. 4. Temperature dependences of the anisotropy and the anisotropy constant K, in Lu,Fe,,C.
field
H,,
This means that the contribution from the Fe sublattice to the magnetocrystalline anisotropy is larger in R,Fe,,C than in R,Fe,,B compounds. The contribution to the magnetic anisotropy arising from the Fe sublattice is usually due to the incompletely quenched orbital angular momentum of the Fe atoms and dipolar interaction between the magnetic moments. The larger number of electrons in the outer shell of C atoms than in B atoms, leads to the transfer of more electrons to the 3d band, resulting in a decrease of the magnetic moment of the Fe atoms. This may lead to a slight decrease in the dipolar anisotropy. Therefore, one may expect that compared with the borides, the slight increase in the magnetic anisotropy of the Fe sublattice may originate from: (1) an increase in the magnetic anisotropy contributed by the orbital moment of the Fe atoms; (2) an increase in the dipolar anisotropy due to the change of lattice parameters; (3) the decrease of saturation magnetization of the carbides. From fig. 4, it can be seen that the anisotropy field of Lu,Fe,,C at 1.5 K is slightly higher than at room temperature. A maximum in the temperature dependence of the anisotropy field is found, whereas no maximum in the temperature dependence of the anisotropy constant is observed. Obviously, the maximum in the temperature dependence of the anisotropy field is less pronounced than that found by various authors for the corresponding boride Lu,Fe,,B [8,9]. The anomalous temperature dependence of the Fe-sublattice
=
K,(O)[~,,(T)/~~,(O)l”[l - ~W,‘].
The disappearance of the anomalous behaviour of K,(T) in Lu,Fe,,C suggests that the change in the crystal-field interactions associated with the magnetovolume anomaly, which occurs in R,Fe,,B compounds below T,,may become less pronounced in Lu,Fe,,C. In dealing with the anomalous temperature dependence of the Fe anisotropy in R,Fe,,B, it has been suggested in ref. [8], that this effect may result from a competition between different temperature dependences of the individual contributions from different Fe sites. It is likely that the effects of such a competition have become less clear in Lu,Fe,,C. On the other hand, our previous investigation has revealed that also in Gd,Fe,,C an anomalous temperature dependence of the Fe anisotropy exists [ll]. It is very likely that the disappearance of the anomalous behaviour in Lu,Fe,,C must be ascribed to the coexistent actions of Lu and C on the magnetocrystalline anisotropy of the Fe sublattice. In conclusion, the saturation magnetization and the magnetic moment per Fe atom of Lu*Fe,,C are slightly smaller than in Lu,Fe,,B, whereas the magnetocrystalline anisotropy of Lu,Fe,,C is found to be larger than in the corresponding boride. The anomalous behaviour in the temperature dependence of the Fe-sublattice anisotropy, as ascribed to the different temperature dependences of the individual contributions from different Fe sites and/or the change of the Fe anisotropy associated with the magnetovolume anomaly, are found to be less pronounced.
Acknowledgements The present work has been carried out within the scientific exchange program between China and The Netherlands and has been partly supported by the Concerted European Action on Magnets (CEAM), the National Natural Sciences Foundation of China and the Magnetism Labora-
222
2. -d. Zhang et ul. / RE
tory of the Institute of Physics, Academia Sinica. The authors greatly appreciate Professor K.H.J. Buschow of the Philips Research Laboratories for providing polycrystalline samples and Professor Fan Shi-yong of the Institute of Physics for help during the magnetization measurements.
References [II F.R. de Boer, Huang Ying-kai, Mooij
and
K.H.J.
Buschow,
Zhang Zhi-dong, J. Magn. Magn.
D.B. de Mat. 72
(1988) 167.
I4 F.R. de Boer, R. Verhoef. Zhang Zhi-dong,
D.B. de Mooij and K.H.J. Buschow, J. Magn. Magn. Mat. 73 (1988) 263. J. [31 K.H.J. Buschow, D.B. de Mooij and C.J.M. Den&en, Less-Common Metals 142 (1988) L13.
TM intermetalltc
Lu, Fe,,C
[4] R. Verhoef, F.R. de Boer. Yang Fuming, Zhang Zhi-dong. B.D. de Mooij and K.H.J. Buschow, J. Magn. Magn. Mat. 80 (1989) 37. [S] Liu Wei. Zhang Zhi-dong, X.K. Sun, Y.C. Chuang. Yang Fuming and F.R. de Boer. Solid State Commun. 76 (1990) 1375. [6] H.R. Kirchmayr and C.A. Poldy. Handbook on the Physics and Chemistry of Rare Earths, eds. K.A. Gschneidner, Jr. and L. Eyring (North-Holland. Amsterdam, 1979) chap. 14. [7] R. Hasegawa and R. Ray, J. Appl. Phys. 49 (1978) 4174. [8] F. Bolzoni, J.P. Gavigan. D. Givord, H.S. Li, 0. Moze and L. Pareti, J. Magn. Magn. Mat. 66 (1987) 158. [9] X.K. Sun, PhD Thesis, Techn. Univ. Vienna (1985). [lo] M.I. Bartashevich and A.V. Andreev, Physica B 162 (1990) 52. [ll] X.C. Kou, X.K. Sun, Y.C. Chuang, T.S. Zhao. R. Grossinger and H.R. Kirchmayr, Solid State Commun. 73 (1990) 87.