- Email: [email protected]
Transport properties in ferromagnet UTeS
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) 1718–1720 www.elsevier.com/locate/jmmm
Transport properties in ferromagnet UTeS Shugo Ikedaa,, Hironori Sakaia, Tatsuma D. Matsudaa, Dai Aokib, Yoshiya Hommab, Etsuji Yamamotoa, Akio Nakamuraa, Yoshinobu Shiokawab, ¯ nukia,c Yoshinori Hagaa, Yoshichika O a
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan b Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan c Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Available online 9 November 2006
Abstract The ferromagnet UTeS with the Curie temperature T C ¼ 87 K has been studied by measuring the magnetoresistance and Hall resistivity. The Hall coefficient at 0.5 T shows a large peak around T C , reflecting the extraordinary Hall effect. The present extraordinary Hall effect was, however, suppressed by applying a magnetic field of 5.5 T. From the results of the electrical resistivity and Hall resistivity measurements, UTeS was found to be a semimetal. r 2006 Published by Elsevier B.V. PACS: 71.55.Ak; 72.15.v; 73.43.Qt Keywords: UTeS; Semimetal
bUX2 (X: S and Se) has the PbCl2 -type orthorhombic crystal structure (space group Pnma) [1,2]. The paramagnet bUS2 and the ferromagnet bUSe2 with the Curie temperature T C ¼ 14 K are semiconductors [1–3]. These chalcogenide atoms X can be replaced each other, as in UTeS, USeS and USe1:28 Te0:72 . The crystal structure of these uranium mixed chalcogenides is isostructural with bUX2 [4,5]. USeS, UTeS and USe1:28 Te0:72 are ferromagnets with Curie temperatures of 24, 87 and 69 K, respectively [4,5]. Recently, we suggested that ferromagnetic moments in UTeS are mainly oriented along the [0 0 1] direction, but slightly canted along [1 0 0]. The electrical resistivity for USeS indicates a semiconducting property, while UTeS and USe1:28 Te0:72 are semimetallic [4,5]. In this paper, we report the results of magnetoresistance and Hall resistivity measurements performed on a single crystal of ferromagnet UTeS grown by the usual chemical transport method. Corresponding author.
E-mail address: [email protected] (S. Ikeda). 0304-8853/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.jmmm.2006.10.545
Fig. 1(a) shows the temperature dependence of the electrical resistivity r at 0 and 5.5 T. Here, a magnetic field is applied along the [0 0 1] direction, perpendicular to the current direction, Jk [0 1 0], which means a transverse magnetoresistance. The absolute value of the electrical resistivity is two orders larger than the usual value of 50–100 mO cm in a uranium-based metallic compound. As shown in Fig. 1(a), the electrical resistivity decreases monotonically with decreasing temperature, but increases slightly below 100 K. Below the Curie temperature T C ¼ 87 K, the resistivity decreases steeply. The resistivity at 5.5 T for Hk [0 0 1] decreases monotonically with decreasing the temperature. The peak structure of the resistivity disappears completely under 5.5 T, indicating a large negative magnetoresistance below 150 K. Simply thinking, the magnetic moments are enhanced to orient along the field direction of the easy-axis, namely [0 0 1] direction, and the electrical resistivity becomes conductive due to a reduction of spindisorder scattering for the conduction electrons, producing a negative magnetoresistance. Similar behavior has been observed for the Hall resistivity measurement. Fig. 1(b) shows the temperature
ARTICLE IN PRESS S. Ikeda et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1718–1720
a
15
6
RH (×10-6 m3/C)
b
ρH /H (×10 -7m3/C)
(mΩ.cm)
UTeS J // [010] 4 Tc 2
0 3
0T
5.5T H // [001]
Tc
UTeS J // [010] H // [001]
1 5.5T 100 200 300 Temperature (K)
Fig. 1. Temperature dependence of (a) zero field electrical resistivity for current J along [0 1 0] and magnetoresistance in a field of 5.5 T directed along [0 0 1] direction and (b) the Hall coefficient at fields of 0.5 and 5.5 T for Hk [0 0 1] in UTeS.
dependence of Hall coefficient RH at 0.5 and 5.5 T for Jk [0 1 0] and Hk [0 0 1]. The Hall coefficient at 0.5 T shows a large peak around T C , reflecting the extraordinary Hall effect. The present extraordinary Hall effect is, however, suppressed by applying a magnetic field of 5.5 T. It is noted that the sign of the Hall coefficient is changed from positive at 0.5 T to negative at 5.5 T at low temperatures. In order to determine the ordinary Hall coefficient, we measured the field dependence of Hall resistivity rH at 10 K. The Hall resistivity at 10 K decreases linearly with increasing magnetic field, and the sign of the Hall resistivity changes from positive to negative at 0.8 T. In the usual magnetic materials, the Hall resistivity is described as follows: @rH @M , ¼ R0 þ fR0 ð1 NÞ þ Rs g @H @H
UTeS J // [010] H //[001] 10 K
5 0
10 M/H (µΒ/Τ)
20
Fig. 2. The rH =H vs M s =H. The solid line represents a fitting line.
0.5T
0
10
-5 0
2
0
1719
(1)
where R0 and Rs are the ordinary and extraordinary Hall coefficients, respectively, N is the demagnetization factor,
M is the magnetization and H is the applied magnetic field [6]. Fig. 2 shows the rH =H vs M=H relation, which corresponds to Eq. (1). The magnetization M for Hk [0 0 1] is saturated and a spontaneous magnetization M ð¼ 1:62 mB Þ is used here. From the result shown in Fig. 2, the ordinary Hall coefficient is estimated to be R0 ¼ 1 107 m3 =C by extrapolating M=H to zero. This value of R0 is larger than that of a usual metallic compound, namely 1010 m3 =C. For example, if we assume that UTeS produces one conduction electron, where the unit cell contains four molecules of UTeS, R0 is calculated as 4:5 1010 m3 =C. From these results, it is concluded that UTeS is a low-carrier compound, namely a semimetal, although we cannot determine the carrier concentration from the present Hall coefficient because of the two-carrier compound with electrons and holes. This result is consistent with the large value of electrical resistivity. In summary, we grew single crystals of ferromagnet UTeS and studied by measuring the magnetoresistance and the Hall resistivity. The magnetic scattering in the electrical resistivity and the extraordinary Hall effect is suppressed by applying a magnetic field of 5.5 T. From the result of the Hall resistivity measurement, UTeS is concluded to be a semimetal. This is consistent with the large value of the electrical resistivity. This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (B), 18740216, 2006. References [1] W. Suski, T. Gibin´ski, A. Wojakowski, A. Czopnik, Phys. Stat. Sol. (a) 9 (1972) 653. [2] G.V. Ellert, G.M. Kuzmicheva, A.A. Eliseev, V.K. Slovyanskikh, S.P. Morozov, Zh. Neorg. Khim. 19 (1974) 45.
ARTICLE IN PRESS 1720
S. Ikeda et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1718–1720
[3] L. Shlyk, R. Troc´, D. Kaczorowski, J. Magn. Magn. Mater. 140–144 (1955) 1435. [4] R. Troc´, D. Kaczorowski, L. Shlyk, M. Potel, H. Noe¨l, J. Phys. Chem. Solids 55 (9) (1994) 815.
[5] S. Ikeda, H. Sakai, D. Aoki, Y. Homma, E. Yamamoto, A. Nakamura, ¯ nuki, J. Phys. Soc. Japan, to be published. Y. Shiokawa, Y. Haga, Y. O [6] C.M. Hurd, The Hall Effect in Metals and Alloys, Plenum Press, New York, 1972 (Chapter 5).
Journal of Magnetism and Magnetic Materials 310 (2007) 1718–1720 www.elsevier.com/locate/jmmm
Transport properties in ferromagnet UTeS Shugo Ikedaa,, Hironori Sakaia, Tatsuma D. Matsudaa, Dai Aokib, Yoshiya Hommab, Etsuji Yamamotoa, Akio Nakamuraa, Yoshinobu Shiokawab, ¯ nukia,c Yoshinori Hagaa, Yoshichika O a
Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan b Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan c Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Available online 9 November 2006
Abstract The ferromagnet UTeS with the Curie temperature T C ¼ 87 K has been studied by measuring the magnetoresistance and Hall resistivity. The Hall coefficient at 0.5 T shows a large peak around T C , reflecting the extraordinary Hall effect. The present extraordinary Hall effect was, however, suppressed by applying a magnetic field of 5.5 T. From the results of the electrical resistivity and Hall resistivity measurements, UTeS was found to be a semimetal. r 2006 Published by Elsevier B.V. PACS: 71.55.Ak; 72.15.v; 73.43.Qt Keywords: UTeS; Semimetal
bUX2 (X: S and Se) has the PbCl2 -type orthorhombic crystal structure (space group Pnma) [1,2]. The paramagnet bUS2 and the ferromagnet bUSe2 with the Curie temperature T C ¼ 14 K are semiconductors [1–3]. These chalcogenide atoms X can be replaced each other, as in UTeS, USeS and USe1:28 Te0:72 . The crystal structure of these uranium mixed chalcogenides is isostructural with bUX2 [4,5]. USeS, UTeS and USe1:28 Te0:72 are ferromagnets with Curie temperatures of 24, 87 and 69 K, respectively [4,5]. Recently, we suggested that ferromagnetic moments in UTeS are mainly oriented along the [0 0 1] direction, but slightly canted along [1 0 0]. The electrical resistivity for USeS indicates a semiconducting property, while UTeS and USe1:28 Te0:72 are semimetallic [4,5]. In this paper, we report the results of magnetoresistance and Hall resistivity measurements performed on a single crystal of ferromagnet UTeS grown by the usual chemical transport method. Corresponding author.
E-mail address: [email protected] (S. Ikeda). 0304-8853/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.jmmm.2006.10.545
Fig. 1(a) shows the temperature dependence of the electrical resistivity r at 0 and 5.5 T. Here, a magnetic field is applied along the [0 0 1] direction, perpendicular to the current direction, Jk [0 1 0], which means a transverse magnetoresistance. The absolute value of the electrical resistivity is two orders larger than the usual value of 50–100 mO cm in a uranium-based metallic compound. As shown in Fig. 1(a), the electrical resistivity decreases monotonically with decreasing temperature, but increases slightly below 100 K. Below the Curie temperature T C ¼ 87 K, the resistivity decreases steeply. The resistivity at 5.5 T for Hk [0 0 1] decreases monotonically with decreasing the temperature. The peak structure of the resistivity disappears completely under 5.5 T, indicating a large negative magnetoresistance below 150 K. Simply thinking, the magnetic moments are enhanced to orient along the field direction of the easy-axis, namely [0 0 1] direction, and the electrical resistivity becomes conductive due to a reduction of spindisorder scattering for the conduction electrons, producing a negative magnetoresistance. Similar behavior has been observed for the Hall resistivity measurement. Fig. 1(b) shows the temperature
ARTICLE IN PRESS S. Ikeda et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1718–1720
a
15
6
RH (×10-6 m3/C)
b
ρH /H (×10 -7m3/C)
(mΩ.cm)
UTeS J // [010] 4 Tc 2
0 3
0T
5.5T H // [001]
Tc
UTeS J // [010] H // [001]
1 5.5T 100 200 300 Temperature (K)
Fig. 1. Temperature dependence of (a) zero field electrical resistivity for current J along [0 1 0] and magnetoresistance in a field of 5.5 T directed along [0 0 1] direction and (b) the Hall coefficient at fields of 0.5 and 5.5 T for Hk [0 0 1] in UTeS.
dependence of Hall coefficient RH at 0.5 and 5.5 T for Jk [0 1 0] and Hk [0 0 1]. The Hall coefficient at 0.5 T shows a large peak around T C , reflecting the extraordinary Hall effect. The present extraordinary Hall effect is, however, suppressed by applying a magnetic field of 5.5 T. It is noted that the sign of the Hall coefficient is changed from positive at 0.5 T to negative at 5.5 T at low temperatures. In order to determine the ordinary Hall coefficient, we measured the field dependence of Hall resistivity rH at 10 K. The Hall resistivity at 10 K decreases linearly with increasing magnetic field, and the sign of the Hall resistivity changes from positive to negative at 0.8 T. In the usual magnetic materials, the Hall resistivity is described as follows: @rH @M , ¼ R0 þ fR0 ð1 NÞ þ Rs g @H @H
UTeS J // [010] H //[001] 10 K
5 0
10 M/H (µΒ/Τ)
20
Fig. 2. The rH =H vs M s =H. The solid line represents a fitting line.
0.5T
0
10
-5 0
2
0
1719
(1)
where R0 and Rs are the ordinary and extraordinary Hall coefficients, respectively, N is the demagnetization factor,
M is the magnetization and H is the applied magnetic field [6]. Fig. 2 shows the rH =H vs M=H relation, which corresponds to Eq. (1). The magnetization M for Hk [0 0 1] is saturated and a spontaneous magnetization M ð¼ 1:62 mB Þ is used here. From the result shown in Fig. 2, the ordinary Hall coefficient is estimated to be R0 ¼ 1 107 m3 =C by extrapolating M=H to zero. This value of R0 is larger than that of a usual metallic compound, namely 1010 m3 =C. For example, if we assume that UTeS produces one conduction electron, where the unit cell contains four molecules of UTeS, R0 is calculated as 4:5 1010 m3 =C. From these results, it is concluded that UTeS is a low-carrier compound, namely a semimetal, although we cannot determine the carrier concentration from the present Hall coefficient because of the two-carrier compound with electrons and holes. This result is consistent with the large value of electrical resistivity. In summary, we grew single crystals of ferromagnet UTeS and studied by measuring the magnetoresistance and the Hall resistivity. The magnetic scattering in the electrical resistivity and the extraordinary Hall effect is suppressed by applying a magnetic field of 5.5 T. From the result of the Hall resistivity measurement, UTeS is concluded to be a semimetal. This is consistent with the large value of the electrical resistivity. This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Young Scientists (B), 18740216, 2006. References [1] W. Suski, T. Gibin´ski, A. Wojakowski, A. Czopnik, Phys. Stat. Sol. (a) 9 (1972) 653. [2] G.V. Ellert, G.M. Kuzmicheva, A.A. Eliseev, V.K. Slovyanskikh, S.P. Morozov, Zh. Neorg. Khim. 19 (1974) 45.
ARTICLE IN PRESS 1720
S. Ikeda et al. / Journal of Magnetism and Magnetic Materials 310 (2007) 1718–1720
[3] L. Shlyk, R. Troc´, D. Kaczorowski, J. Magn. Magn. Mater. 140–144 (1955) 1435. [4] R. Troc´, D. Kaczorowski, L. Shlyk, M. Potel, H. Noe¨l, J. Phys. Chem. Solids 55 (9) (1994) 815.
[5] S. Ikeda, H. Sakai, D. Aoki, Y. Homma, E. Yamamoto, A. Nakamura, ¯ nuki, J. Phys. Soc. Japan, to be published. Y. Shiokawa, Y. Haga, Y. O [6] C.M. Hurd, The Hall Effect in Metals and Alloys, Plenum Press, New York, 1972 (Chapter 5).