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Magnetic properties of UFexCo10-xSi2 intermetallics
Journal of Magnetism North-Holland
and Magnetic
Materials
L133
95 (1991) L133-L136
Letter to the Editor
Magnetic properties of UFe,Co,,_,Si,
intermetallics
W. Suski, A. Baran, K. Wochowski W. Trzebintowski Institute of Low Temperature 50-950 Wroclaw 2, Poland
and Structure Research, Polish Academy
of Sciences, P.O. Box 937,
and T. Mydlarz International Received
Laboratory
2 November
of High Magnetic Fields and Low Temperatures, 1990; in revised
form 14 January
95 Pr&hnika
Str., 53-529 Wroclaw, Poland
1991
UFe,,Si, and UCo,,Si, form solid solution with the ThMn,, type of tetragonal structure. The lattice parameter a follows the Vegard law and parameter c does not. The increase of cobalt content depresses a saturation magnetization at 4.2 K almost linearly, whereas the remanence for all samples is very low. The highest Curie point equal to 750 K is observed for UFesCo,Si,. The annealing process does not affect the Curie point of these materials, however increases slightly the saturation magnetization. Two samples from the U(Fe, Co, Al),,Siz system have been investigated too.
Fe-rich ternary compounds of the rare earths derived from the tetragonal ThMn,, structure have been proposed as inexpensive alternative permanent magnetic materials [l]. We have succeeded in obtaining UFe,,Si, [2] with the Curie points as high as 650 K and a magnetization value sufficient for technical applications, however, with very low remanence. To improve this drawback a preoriented sample has been prepared, but this procedure does not increase the remanence markedly [3]. UCo,,Si, turned out to be a ferromagnet below 550 K, but with a lower saturation magnetization than the former one and also with low remanence. Both these compounds exhibit an identical domain structure [4]. The pseudoternary compounds of R(Fe, Co)iOM,-type exhibit considerable improvement of some magnetic parameters [5-141 and therefore we decided to obtain U(Fe, Co),&, alloys. These alloys were prepared as was described previously [2,3]. The X-ray diagrams were single phases, all reflection belonging to the ThMn,,-type structure. 0304-8853/91/$03.50
0 1991 - Elsevier Science Publishers
As one can see from fig. 1 the lattice parameter a follows the Vegard law whereas the c parameter does not. Fig. 2 shows that at low temperatures the magnetization of the alloys at the beginning increases almost linearly with magnetic field and then, as the field further increases for samples with the lower Co content, saturation is observed. The field of saturation B, increases as the Co content increases and for x I 4 B, is not observed as for UCo,,Si, [3]. The addition of Al decreases the magnetization compared with alloys with the same Fe concentration. The almost monotonic decrease of saturation magnetization at 4.2 K (see fig. 1) is exceptional because for the rare earth compounds a maximum is observed for about 80% of Fe [8-121. In the present case there is practically no difference between x = 10 and 8 and it is difficult to distinguish any maximum. Demonstrated in fig. 3, a temperature dependence of magnetization shows a pronounced decrease for 550-750 K and some tails at 1000-1150 K. These tails most probably
B.V. (North-Holland)
L134
W. Suski et al. /
Magneticproperties of lJFe,Co,, _ ,Si, intemzetallics
result from an impurity of Fe or Co. It follows from fig. 4 that the Al alloys do not exhibit any tail. Most probably the Al admixture has some metallurgical influence improving the sample quality. The addition of Co increases the Curie point, and the highest, equal to 750 K is observed for x = 6 (fig. 1). The annealing does not affect the Curie point of these alloys. For RE compounds the addition of Co increases strongly the Curie point and usually RCo,,M, compounds in the contrary to UCo,,Si, [3] exhibits a higher Curie point than their iron homologue [6-111. Only for Y(Fe, Co),,V, alloys the maximum for 50% of substitution is observed [12]. It follows from fig. 1 that the addition of Co does not increase the remanence markedly. The same behaviour has been observed for Nd(Fe, Co),,Ti, [6]
t T- 1.21 K
4.0
A---_--_
6.0
6.0 Mognetlc
10.0
12.0
14.0
field IT1
Fig. 2. Magnetization of UFexCo,,_,Siz solid solutions and UFe,AlSi, and UF,AlCo,Si, versus magnetic field at 4.2 K.
aIrI 3.838 1.834 3.830 3.826
I
02468' ConcentrationxFig. 1. Saturation magnetization, remanence (both at 4.2 K), Curie points and lattice parameters (at room temperature) of UFexCo,o_xSi, solid solution versus Fe concentration x.
and Y(Fe, Co),iTi [8] systems. Therefore, one can conclude that the Co addition does not improve magnetic properties of U(Fe, Co),&, as far as the remanence is concerned. Also the Al addition has no impact on remanence (fig. 2) but decreases the Curie point (fig. 4) compared to corresponding U-(Fe, Co)-Si compounds. It might be that the improvement can be reached by a different technological process e.g. melt spinning [6] or other rapid solidification processes [15]. Unfortunately, at present we cannot propose any model of substitution of iron atoms through Co or/and Al atoms. We hope that soon we will produce an answer resulting from Mbsbauer experiment which is carried out in our Laboratory now. Another difficult question is the uranium contribution to the magnetic properties of these compounds. In contrary to Br;inde et al. [16], Van Engelen and Buschow [17] claim that the U-sublattice contributes to the Kerr effect in UFe,,Si,.
L135
U? &ski et al. / Magnetic properties of lJFe,Co,, _ xSil intermetailics
Temperature Fig. 3. Magnetization
of UFexCoI,_,Si2
solid solutions
Andreev [18] informs that the magnetostriction of UFe,,Si, is apparently different from that for ThFe,$i, suggesting an influence of the uranium sublattice. Above presented results have a preliminary character and at least three questions remain to be answered :
[Kl
versus temperature
under magnetic
field of 0.3 T.
structure should be performed. As far as we know only one theoretical paper concerning YFe,,_,M, compounds was published [20] as yet.
1) How to improve magnetic properties of U(Fe, M),,Mi compounds? 2) What is the distribution of M (M = Co, Ni, Cu, Al) and M’ (M’ = Si, MO, etc.) atoms in the available crystallographic positions and what factor is deciding in this distribution? E.g. Chevalier [19] claims that for UCo,$i, Si is located in one crystallographic position, whereas for UFe,,Si, in two. 3) What is the uranium contribution to the magnetic properties of the ThMn,,-type materials? To answer these questions much more experimental data obtained in more sophisticated experiments should be collected and calculation of band
Temperature Fig. 4. Magnetization temperature
A
UFegAISig
l
UFe6AICo3Si2
[K I
of UFqAlSi, and UFqA1Co,Si2 under magnetic field of 0.48 T.
versus
L136
W. Suski et al. /
Magneticproperties of UFe,Co,, _ ,Si, intermetallics
References [l] B.D. de Mooij and K.H.J. Buschow, Philips J. Res. 42 (1987) 246. PI W. St&i, A. Baran and T. Mydlarz, Phys. Lett. A 136 (1989) 89. [31 A. Baran, M. Lukasik, W. Suski, J. Suwalski, H. Figiel, J. Opila, K. Turek and T. Mydlarz, J. Magn. Magn. Mat. 83 (1990) 262. [41 J. Wyslocki, W. Suski and A. Baran, J. Less-Common Met. 163 (1990) 115. Y. Tawara, R. Osugi, J. Sakurai and Y. 151 K. Ohashi, Komura, J. Less-Common Met. 139 (1988) Ll. and 161 E.W. Singleton, J. Strzeszewski, G.C. Hadjipanayais D.J. Sellmyer, J. Appl. Phys. 64 (1988) 5717. [71 K.H.J. Buschow, D.B. de Mooij, M. Brouha, H.H.A. Smit and R.C. Thiel, IEEE Trans. Magn. MAG-24 (1988) 1611. 181 Y.C. Yang, S. Hong, Z.Y. Zhang, L. Tong and J.L. Gao, Solid State Commun. 68 (1988) 175. 191 S.F. Cheng, V.K. Sinha, Y. Xu, J.M. Elbicki, E.B. Boltich, W.E. Wallace, S.G. Sankar and D.E. Laughlin, J. Magn. Magn. Mat. 75 (1988) 330.
[lo] A.V. Andreev, A.N. Bogatkin, N.V. Kudrevatykh, S.S. Sigaev and E.N. Tarasov, Fiz. Met. Metall. 68 (1989) 70. [ll] V.K. Sinha, SF. Cheng, W.E. Wallace and S.G. Sankar, J. Magn. Magn. Mat. 81 (1988) 227. [12] M. Jurczyk and 0.0. Chistyakov, J. Magn. Magn. Mat. 82 (1989) 239. [13] M. Solzi, R.H. Xue and L. Pareti, J. Magn. Magn. Mat. 88 (1990) 44. [14] Ying-Chang Yang, Lin-Shu Kong, Hong Sun, Ji Lian Yang, Yang-Fan Ding, Bai-Shen Zhang, Chun-Tang Ye and Lan Jin, J. Appl. Phys. 67 (1990) 4632. [15] L. Schultz, K. Schnitzke and J. Wecker, J. Magn. Magn. Mat. 83 (1990) 254. [16] H. Brlnde, J. Schoenes, F. Hulliger and W. Reim, IEEE Trans. on Magn. MAG-26 (1990) 2795. [17] P.P.J. van Engelen and K.H.J. Buschow, J. Magn. Magn. Mat. 84 (1990) 47. [18] A.V. Andreev, private communication. 1191 M. Chevalier, private communication. [20] R. Coehoorn, Phys. Rev. B 41 (1990) 11790.
and Magnetic
Materials
L133
95 (1991) L133-L136
Letter to the Editor
Magnetic properties of UFe,Co,,_,Si,
intermetallics
W. Suski, A. Baran, K. Wochowski W. Trzebintowski Institute of Low Temperature 50-950 Wroclaw 2, Poland
and Structure Research, Polish Academy
of Sciences, P.O. Box 937,
and T. Mydlarz International Received
Laboratory
2 November
of High Magnetic Fields and Low Temperatures, 1990; in revised
form 14 January
95 Pr&hnika
Str., 53-529 Wroclaw, Poland
1991
UFe,,Si, and UCo,,Si, form solid solution with the ThMn,, type of tetragonal structure. The lattice parameter a follows the Vegard law and parameter c does not. The increase of cobalt content depresses a saturation magnetization at 4.2 K almost linearly, whereas the remanence for all samples is very low. The highest Curie point equal to 750 K is observed for UFesCo,Si,. The annealing process does not affect the Curie point of these materials, however increases slightly the saturation magnetization. Two samples from the U(Fe, Co, Al),,Siz system have been investigated too.
Fe-rich ternary compounds of the rare earths derived from the tetragonal ThMn,, structure have been proposed as inexpensive alternative permanent magnetic materials [l]. We have succeeded in obtaining UFe,,Si, [2] with the Curie points as high as 650 K and a magnetization value sufficient for technical applications, however, with very low remanence. To improve this drawback a preoriented sample has been prepared, but this procedure does not increase the remanence markedly [3]. UCo,,Si, turned out to be a ferromagnet below 550 K, but with a lower saturation magnetization than the former one and also with low remanence. Both these compounds exhibit an identical domain structure [4]. The pseudoternary compounds of R(Fe, Co)iOM,-type exhibit considerable improvement of some magnetic parameters [5-141 and therefore we decided to obtain U(Fe, Co),&, alloys. These alloys were prepared as was described previously [2,3]. The X-ray diagrams were single phases, all reflection belonging to the ThMn,,-type structure. 0304-8853/91/$03.50
0 1991 - Elsevier Science Publishers
As one can see from fig. 1 the lattice parameter a follows the Vegard law whereas the c parameter does not. Fig. 2 shows that at low temperatures the magnetization of the alloys at the beginning increases almost linearly with magnetic field and then, as the field further increases for samples with the lower Co content, saturation is observed. The field of saturation B, increases as the Co content increases and for x I 4 B, is not observed as for UCo,,Si, [3]. The addition of Al decreases the magnetization compared with alloys with the same Fe concentration. The almost monotonic decrease of saturation magnetization at 4.2 K (see fig. 1) is exceptional because for the rare earth compounds a maximum is observed for about 80% of Fe [8-121. In the present case there is practically no difference between x = 10 and 8 and it is difficult to distinguish any maximum. Demonstrated in fig. 3, a temperature dependence of magnetization shows a pronounced decrease for 550-750 K and some tails at 1000-1150 K. These tails most probably
B.V. (North-Holland)
L134
W. Suski et al. /
Magneticproperties of lJFe,Co,, _ ,Si, intemzetallics
result from an impurity of Fe or Co. It follows from fig. 4 that the Al alloys do not exhibit any tail. Most probably the Al admixture has some metallurgical influence improving the sample quality. The addition of Co increases the Curie point, and the highest, equal to 750 K is observed for x = 6 (fig. 1). The annealing does not affect the Curie point of these alloys. For RE compounds the addition of Co increases strongly the Curie point and usually RCo,,M, compounds in the contrary to UCo,,Si, [3] exhibits a higher Curie point than their iron homologue [6-111. Only for Y(Fe, Co),,V, alloys the maximum for 50% of substitution is observed [12]. It follows from fig. 1 that the addition of Co does not increase the remanence markedly. The same behaviour has been observed for Nd(Fe, Co),,Ti, [6]
t T- 1.21 K
4.0
A---_--_
6.0
6.0 Mognetlc
10.0
12.0
14.0
field IT1
Fig. 2. Magnetization of UFexCo,,_,Siz solid solutions and UFe,AlSi, and UF,AlCo,Si, versus magnetic field at 4.2 K.
aIrI 3.838 1.834 3.830 3.826
I
02468' ConcentrationxFig. 1. Saturation magnetization, remanence (both at 4.2 K), Curie points and lattice parameters (at room temperature) of UFexCo,o_xSi, solid solution versus Fe concentration x.
and Y(Fe, Co),iTi [8] systems. Therefore, one can conclude that the Co addition does not improve magnetic properties of U(Fe, Co),&, as far as the remanence is concerned. Also the Al addition has no impact on remanence (fig. 2) but decreases the Curie point (fig. 4) compared to corresponding U-(Fe, Co)-Si compounds. It might be that the improvement can be reached by a different technological process e.g. melt spinning [6] or other rapid solidification processes [15]. Unfortunately, at present we cannot propose any model of substitution of iron atoms through Co or/and Al atoms. We hope that soon we will produce an answer resulting from Mbsbauer experiment which is carried out in our Laboratory now. Another difficult question is the uranium contribution to the magnetic properties of these compounds. In contrary to Br;inde et al. [16], Van Engelen and Buschow [17] claim that the U-sublattice contributes to the Kerr effect in UFe,,Si,.
L135
U? &ski et al. / Magnetic properties of lJFe,Co,, _ xSil intermetailics
Temperature Fig. 3. Magnetization
of UFexCoI,_,Si2
solid solutions
Andreev [18] informs that the magnetostriction of UFe,,Si, is apparently different from that for ThFe,$i, suggesting an influence of the uranium sublattice. Above presented results have a preliminary character and at least three questions remain to be answered :
[Kl
versus temperature
under magnetic
field of 0.3 T.
structure should be performed. As far as we know only one theoretical paper concerning YFe,,_,M, compounds was published [20] as yet.
1) How to improve magnetic properties of U(Fe, M),,Mi compounds? 2) What is the distribution of M (M = Co, Ni, Cu, Al) and M’ (M’ = Si, MO, etc.) atoms in the available crystallographic positions and what factor is deciding in this distribution? E.g. Chevalier [19] claims that for UCo,$i, Si is located in one crystallographic position, whereas for UFe,,Si, in two. 3) What is the uranium contribution to the magnetic properties of the ThMn,,-type materials? To answer these questions much more experimental data obtained in more sophisticated experiments should be collected and calculation of band
Temperature Fig. 4. Magnetization temperature
A
UFegAISig
l
UFe6AICo3Si2
[K I
of UFqAlSi, and UFqA1Co,Si2 under magnetic field of 0.48 T.
versus
L136
W. Suski et al. /
Magneticproperties of UFe,Co,, _ ,Si, intermetallics
References [l] B.D. de Mooij and K.H.J. Buschow, Philips J. Res. 42 (1987) 246. PI W. St&i, A. Baran and T. Mydlarz, Phys. Lett. A 136 (1989) 89. [31 A. Baran, M. Lukasik, W. Suski, J. Suwalski, H. Figiel, J. Opila, K. Turek and T. Mydlarz, J. Magn. Magn. Mat. 83 (1990) 262. [41 J. Wyslocki, W. Suski and A. Baran, J. Less-Common Met. 163 (1990) 115. Y. Tawara, R. Osugi, J. Sakurai and Y. 151 K. Ohashi, Komura, J. Less-Common Met. 139 (1988) Ll. and 161 E.W. Singleton, J. Strzeszewski, G.C. Hadjipanayais D.J. Sellmyer, J. Appl. Phys. 64 (1988) 5717. [71 K.H.J. Buschow, D.B. de Mooij, M. Brouha, H.H.A. Smit and R.C. Thiel, IEEE Trans. Magn. MAG-24 (1988) 1611. 181 Y.C. Yang, S. Hong, Z.Y. Zhang, L. Tong and J.L. Gao, Solid State Commun. 68 (1988) 175. 191 S.F. Cheng, V.K. Sinha, Y. Xu, J.M. Elbicki, E.B. Boltich, W.E. Wallace, S.G. Sankar and D.E. Laughlin, J. Magn. Magn. Mat. 75 (1988) 330.
[lo] A.V. Andreev, A.N. Bogatkin, N.V. Kudrevatykh, S.S. Sigaev and E.N. Tarasov, Fiz. Met. Metall. 68 (1989) 70. [ll] V.K. Sinha, SF. Cheng, W.E. Wallace and S.G. Sankar, J. Magn. Magn. Mat. 81 (1988) 227. [12] M. Jurczyk and 0.0. Chistyakov, J. Magn. Magn. Mat. 82 (1989) 239. [13] M. Solzi, R.H. Xue and L. Pareti, J. Magn. Magn. Mat. 88 (1990) 44. [14] Ying-Chang Yang, Lin-Shu Kong, Hong Sun, Ji Lian Yang, Yang-Fan Ding, Bai-Shen Zhang, Chun-Tang Ye and Lan Jin, J. Appl. Phys. 67 (1990) 4632. [15] L. Schultz, K. Schnitzke and J. Wecker, J. Magn. Magn. Mat. 83 (1990) 254. [16] H. Brlnde, J. Schoenes, F. Hulliger and W. Reim, IEEE Trans. on Magn. MAG-26 (1990) 2795. [17] P.P.J. van Engelen and K.H.J. Buschow, J. Magn. Magn. Mat. 84 (1990) 47. [18] A.V. Andreev, private communication. 1191 M. Chevalier, private communication. [20] R. Coehoorn, Phys. Rev. B 41 (1990) 11790.