- Email: [email protected]
Magnetic and Fermi surface properties of UNiGa5
Physica B 312–313 (2002) 294–296
Magnetic and Fermi surface properties of UNiGa5 Yoshihumi Tokiwaa,b,*, Yoshinori Hagab, Naoto Metokib, a,b % Shuugo Ikedaa, Rikio Settaia, Yoshichika Onuki a
b
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Abstract In order to investigate the magnetic structure and Fermi surface properties of UNiGa5 ; we have performed elastic neutron scattering and de Haas-van Alphen(dHvA) experiments. In the neutron scattering experiment using a single crystalline sample, we determined the antiferromagnetic propagation vector Q ¼ ð1=2; 1=2; 1=2Þ in UNiGa5 : In the dHvA experiment, we observed four branches. Two branches indicate cylindrical Fermi surface and the other two branches correspond to ellipsoidal ones. The cyclotron mass was not large, ranging from 1.3 to 3.1m0 : r 2002 Elsevier Science B.V. All rights reserved. Keywords: UNiGa5 ; Magnetic structure; Fermi surface
UNiGa5 has the HoCoGa5 -type tetragonal crystal structure (P4/mmm #123 D14h ) [1] which is the same structure of new ternary heavy fermion compounds of CeTIn5 ðT ¼ Co; Rh; IrÞ: It orders antiferromagnetically below TN ¼ 85:5 K and the electronic specific heat coefficient g is 40 mJ=K2 mol [2,3]. There found a small hump in the electrical resistivity at TN ; which is reminiscent of the spin density wave formation. The susceptibility above TN shows an almost temperatureindependent susceptibility and extremely small anisotropy. These properties in UNiGa5 are quite similar to those in UGa3 which is supposed to have an itinerant 5felectron nature [4]. In order to clarify the magnetic and electronic ground states of UNiGa5 we performed the elastic neutron scattering experiment with a single crystal sample and de Haas-van Alphen(dHvA) experiment. Single crystals were grown by the self-flux method. The off-stoichiometric amounts of U, Ni and Ga in the *Corresponding author. Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan. Tel.: +81-29-284-6735; fax: +81-29-2825927. E-mail address: [email protected] (Y. Tokiwa).
atomic ratio 1:1:15 were put into the alumina crucible and sealed in the quartz tube with Ar atmosphere. The materials were heated to 10101C and slowly cooled to 6001C. Many single crystals were grown by this method. The residual resistivity ratio rRT =r0 was 130, indicating high-quality samples. Neutron scattering experiments were carried out at JRR-3M at Japan Atomic Energy Research Institute using a thermal neutron triple-axis spectrometer TAS1. We used monochromatized neutron beam with the wave ( length of 2:3590 A: In the neutron scattering experiment we observed magnetic reflections of ð1=2 þ h; 1=2 þ k; 1=2 þ lÞ at 10 K: For example, Fig. 1 shows the neutron scattering profile of ð3=2; 3=2; 3=2Þ magnetic Bragg peak at several temperatures. The temperature independent peak at 2y ¼ 71:31 is the ð2; 0; 0Þ Bragg peak of Al metal from the sample cell. These magnetic peaks disappear above TN ¼ 86 K: Therefore, UNiGa5 is an antiferromagnet with the Q ¼ ð1=2; 1=2; 1=2Þ below TN ¼ 86 K: Since the magnetic susceptibility for the field along [0 0 1] is smaller than that for [1 0 0] below TN [3], the ordered magnetic moment is expected to be along [0 0 1]. As shown in Table 1, the calculated integrated intensity with the magnetic moment along [0 0 1] agrees with the observed intensity at 10 K better than that with the
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 3 2 1 - 7
Y. Tokiwa et al. / Physica B 312–313 (2002) 294–296
295
Fig. 1. Temperature dependence of magnetic peak profile of ð3=2; 3=2; 3=2Þ in UNiGa5 :
Table 1 Observed and calculated integrated intensity of magnetic reflection of UNiGa5 at 10 K: Ical1 and Ical2 are the calculated intensities with the magnetic moment parallel to [0 0 1] and [1 0 0], respectively h
k
l
Iobs
Ical1
Ical2
1=2 1=2 3=2 1=2 3=2 3=2 1=2
1=2 1=2 3=2 1=2 3=2 3=2 1=2
7=2 1=5 5=2 3=2 3=2 1=2 1=2
54 143 215 369 388 548 1493
36 112 189 413 314 426 1584
376 637 254 1054 313 351 1582
moment along [1 0 0]. In the calculation, the magnetic form factor was approximated to be the same as that of a free ion of U4þ or U3þ [5]. The magnetic moment was estimated to be 0:9ð0:1ÞmB =U by comparing the magnetic peak intensity to the nuclear peaks with the scattering length published in Ref. [6]. Next we studied the Fermi surface property of the conduction electrons by the dHvA effect. Because of the flat Brillouine zone, cylindrical Fermi surfaces are expected to be found in UNiGa5 : Fig. 2 shows the angular dependence of the dHvA frequency F ð¼ _cSF =2peÞ; which is proportional to the external (maximum and minimum) cross-sectional area SF of the Fermi surface. We observed four branches of a1 ; a2 ; b and g: The dHvA frequency of branches a1 and a2 follow a 1=cos y-dependence, indicating one or two cylindrical Fermi surfaces. Usually the cylindrical Fermi surface is slightly corrugated, having maximum and minimum cross-sections, which might correspond to branches a1 and a2 ; respectively. Branches b and g indicate two ellipsoidal Fermi surfaces. We determined
Fig. 2. Angular dependence of dHvA frequency in UNiGa5 :
the cyclotron effective mass from the temperature dependence of the dHvA amplitude. The cyclotron mass was determined as 1.4m0 for branch a1 ; 3.1m0 for a2 ; 1.4m0 for b and 3.1m0 for g for the field along [0 0 1]. The detected cyclotron masses are by one order smaller than those expected from the electronic specific heat coefficient g ¼ 40 mJ=K2 mol [3]. It means that the other larger Fermi surfaces with much larger masses should exist in UNiGa5 : These are left for future study.
Acknowledgements The present work was financially supported by the Grant-in-Aid for Scientific Research COE(10CE2004) and the Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture. Y. Tokiwa acknowledges the support from the Japan Society for the Promotion of Science in frames of the Research Fellowship for Young Scientists.
References [1] Yu.N. Grin, P. Rogl, K. Hiebl, J. Less Common Met. 121 (1986) 497. [2] K. Okuda, S. Noguchi, in: T. Kasuya, T. Ishii, T. # T. Saso (Eds.), Physical Komatsubara, O. Sakai, N. Mori, properties of Actinide and Rare Earth Compounds, Jpn. J. Appl. Phys. Ser. 8 (1993) 32. [3] Y. Tokiwa, Y. Haga, E. Yamamoto, D. Aoki, N. Watanabe, R. Settai, T. Inoue, K. Kindo, H. Harima, % Y. Onuki, J. Phys. Soc. Japan 70 (2001) 1744.
296
Y. Tokiwa et al. / Physica B 312–313 (2002) 294–296
. [4] D. Kaczorowski, R. Tro!c, D. Badurski, A. Bohm, L. Shlyk, F. Steglich, Phys. Rev. B 48 (1993) 16 425. [5] A.J. Freeman, J.P. Desclaux, G.H. Lander, J. Faber Jr., Phys. Rev. B 13 (1976) 1168.
[6] V.F. Sears, in: A.J.C. Willson (Ed.), International Tables for Crystallography, Vol. C, Kluwer Academic Publisher, Dordrecht, 1992, p. 383.
Magnetic and Fermi surface properties of UNiGa5 Yoshihumi Tokiwaa,b,*, Yoshinori Hagab, Naoto Metokib, a,b % Shuugo Ikedaa, Rikio Settaia, Yoshichika Onuki a
b
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
Abstract In order to investigate the magnetic structure and Fermi surface properties of UNiGa5 ; we have performed elastic neutron scattering and de Haas-van Alphen(dHvA) experiments. In the neutron scattering experiment using a single crystalline sample, we determined the antiferromagnetic propagation vector Q ¼ ð1=2; 1=2; 1=2Þ in UNiGa5 : In the dHvA experiment, we observed four branches. Two branches indicate cylindrical Fermi surface and the other two branches correspond to ellipsoidal ones. The cyclotron mass was not large, ranging from 1.3 to 3.1m0 : r 2002 Elsevier Science B.V. All rights reserved. Keywords: UNiGa5 ; Magnetic structure; Fermi surface
UNiGa5 has the HoCoGa5 -type tetragonal crystal structure (P4/mmm #123 D14h ) [1] which is the same structure of new ternary heavy fermion compounds of CeTIn5 ðT ¼ Co; Rh; IrÞ: It orders antiferromagnetically below TN ¼ 85:5 K and the electronic specific heat coefficient g is 40 mJ=K2 mol [2,3]. There found a small hump in the electrical resistivity at TN ; which is reminiscent of the spin density wave formation. The susceptibility above TN shows an almost temperatureindependent susceptibility and extremely small anisotropy. These properties in UNiGa5 are quite similar to those in UGa3 which is supposed to have an itinerant 5felectron nature [4]. In order to clarify the magnetic and electronic ground states of UNiGa5 we performed the elastic neutron scattering experiment with a single crystal sample and de Haas-van Alphen(dHvA) experiment. Single crystals were grown by the self-flux method. The off-stoichiometric amounts of U, Ni and Ga in the *Corresponding author. Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan. Tel.: +81-29-284-6735; fax: +81-29-2825927. E-mail address: [email protected] (Y. Tokiwa).
atomic ratio 1:1:15 were put into the alumina crucible and sealed in the quartz tube with Ar atmosphere. The materials were heated to 10101C and slowly cooled to 6001C. Many single crystals were grown by this method. The residual resistivity ratio rRT =r0 was 130, indicating high-quality samples. Neutron scattering experiments were carried out at JRR-3M at Japan Atomic Energy Research Institute using a thermal neutron triple-axis spectrometer TAS1. We used monochromatized neutron beam with the wave ( length of 2:3590 A: In the neutron scattering experiment we observed magnetic reflections of ð1=2 þ h; 1=2 þ k; 1=2 þ lÞ at 10 K: For example, Fig. 1 shows the neutron scattering profile of ð3=2; 3=2; 3=2Þ magnetic Bragg peak at several temperatures. The temperature independent peak at 2y ¼ 71:31 is the ð2; 0; 0Þ Bragg peak of Al metal from the sample cell. These magnetic peaks disappear above TN ¼ 86 K: Therefore, UNiGa5 is an antiferromagnet with the Q ¼ ð1=2; 1=2; 1=2Þ below TN ¼ 86 K: Since the magnetic susceptibility for the field along [0 0 1] is smaller than that for [1 0 0] below TN [3], the ordered magnetic moment is expected to be along [0 0 1]. As shown in Table 1, the calculated integrated intensity with the magnetic moment along [0 0 1] agrees with the observed intensity at 10 K better than that with the
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 3 2 1 - 7
Y. Tokiwa et al. / Physica B 312–313 (2002) 294–296
295
Fig. 1. Temperature dependence of magnetic peak profile of ð3=2; 3=2; 3=2Þ in UNiGa5 :
Table 1 Observed and calculated integrated intensity of magnetic reflection of UNiGa5 at 10 K: Ical1 and Ical2 are the calculated intensities with the magnetic moment parallel to [0 0 1] and [1 0 0], respectively h
k
l
Iobs
Ical1
Ical2
1=2 1=2 3=2 1=2 3=2 3=2 1=2
1=2 1=2 3=2 1=2 3=2 3=2 1=2
7=2 1=5 5=2 3=2 3=2 1=2 1=2
54 143 215 369 388 548 1493
36 112 189 413 314 426 1584
376 637 254 1054 313 351 1582
moment along [1 0 0]. In the calculation, the magnetic form factor was approximated to be the same as that of a free ion of U4þ or U3þ [5]. The magnetic moment was estimated to be 0:9ð0:1ÞmB =U by comparing the magnetic peak intensity to the nuclear peaks with the scattering length published in Ref. [6]. Next we studied the Fermi surface property of the conduction electrons by the dHvA effect. Because of the flat Brillouine zone, cylindrical Fermi surfaces are expected to be found in UNiGa5 : Fig. 2 shows the angular dependence of the dHvA frequency F ð¼ _cSF =2peÞ; which is proportional to the external (maximum and minimum) cross-sectional area SF of the Fermi surface. We observed four branches of a1 ; a2 ; b and g: The dHvA frequency of branches a1 and a2 follow a 1=cos y-dependence, indicating one or two cylindrical Fermi surfaces. Usually the cylindrical Fermi surface is slightly corrugated, having maximum and minimum cross-sections, which might correspond to branches a1 and a2 ; respectively. Branches b and g indicate two ellipsoidal Fermi surfaces. We determined
Fig. 2. Angular dependence of dHvA frequency in UNiGa5 :
the cyclotron effective mass from the temperature dependence of the dHvA amplitude. The cyclotron mass was determined as 1.4m0 for branch a1 ; 3.1m0 for a2 ; 1.4m0 for b and 3.1m0 for g for the field along [0 0 1]. The detected cyclotron masses are by one order smaller than those expected from the electronic specific heat coefficient g ¼ 40 mJ=K2 mol [3]. It means that the other larger Fermi surfaces with much larger masses should exist in UNiGa5 : These are left for future study.
Acknowledgements The present work was financially supported by the Grant-in-Aid for Scientific Research COE(10CE2004) and the Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture. Y. Tokiwa acknowledges the support from the Japan Society for the Promotion of Science in frames of the Research Fellowship for Young Scientists.
References [1] Yu.N. Grin, P. Rogl, K. Hiebl, J. Less Common Met. 121 (1986) 497. [2] K. Okuda, S. Noguchi, in: T. Kasuya, T. Ishii, T. # T. Saso (Eds.), Physical Komatsubara, O. Sakai, N. Mori, properties of Actinide and Rare Earth Compounds, Jpn. J. Appl. Phys. Ser. 8 (1993) 32. [3] Y. Tokiwa, Y. Haga, E. Yamamoto, D. Aoki, N. Watanabe, R. Settai, T. Inoue, K. Kindo, H. Harima, % Y. Onuki, J. Phys. Soc. Japan 70 (2001) 1744.
296
Y. Tokiwa et al. / Physica B 312–313 (2002) 294–296
. [4] D. Kaczorowski, R. Tro!c, D. Badurski, A. Bohm, L. Shlyk, F. Steglich, Phys. Rev. B 48 (1993) 16 425. [5] A.J. Freeman, J.P. Desclaux, G.H. Lander, J. Faber Jr., Phys. Rev. B 13 (1976) 1168.
[6] V.F. Sears, in: A.J.C. Willson (Ed.), International Tables for Crystallography, Vol. C, Kluwer Academic Publisher, Dordrecht, 1992, p. 383.