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Magnetic properties of single crystals of RCoIn5(R=Tb,Dy,Ho,Er,Yb)
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 635–636
Magnetic properties of single crystals of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ Y. Isikawa*, D. Kato, A. Mitsuda, T. Mizushima, T. Kuwai Department of Physics, Toyama University, Toyama 930-8555, Japan
Abstract The magnetic susceptibility w and magnetization of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ have been investigated using single crystalline samples. The 1=w curves obey the Curie–Weiss law for all compounds except R ¼ Yb: Easy axis of the magnetization is found to be parallel to the c-axis for R ¼ Tb; Dy; Ho; and in the ab plane for R ¼ Er: Below TN ; metamagnetic transitions with multi-step jumps are observed for R ¼ Dy and Ho. The temperature dependence of 1=w curves has been systematically analyzed for all the compounds except R ¼ Yb: r 2003 Elsevier B.V. All rights reserved. PACS: 75.30.Gw Keywords: RCoIn5 ; Single crystal; Magnetic susceptibility; Metamagnetic transition; Easy axis of magnetization
In the heavy fermion superconductor CeCoIn5 [1], a field-induced metamagnetic transition has been observed in the magnetic field applied parallel to the ½1 1 0 direction [2]. This transition appears at 1:4 K and persists to at least 25 K which is much higher than its superconducting transition temperature. It is interesting to compare these behaviors of CeCoIn5 to those of compounds which have not any characters such as Kondo effects. We aim to present the magnetic anisotropy and metamagnetic behaviors of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ: The magnetic susceptibility and magnetization of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ have been measured using single crystalline samples which are grown by the In-flux method. These compounds crystallize in the tetragonal crystal structure, and the magnetic atoms R occupy only the corners of the unit cell. The temperature dependence of the magnetic susceptibility w shows the antiferromagnetic behaviors with negative paramagnetic Curie temperatures, and the reciprocal susceptibility obeys the Curie–Weiss law originated from the trivalent rare-earth atoms except *Corresponding author. Tel.: +81-76-445-6583; fax:+81-76445-6549. E-mail address: [email protected] (Y. Isikawa).
R ¼ Yb: As for the exceptional YbCoIn5 ; the value of w is very small, indicating a Pauli paramagnet with divalent Yb atoms. Easy axis of the magnetization is found to be parallel to the c-axis for R ¼ Tb; Dy; Ho; and in the ab plane for R ¼ Er as shown in Fig. 1. The Ne! el temperature, TN ; is 30:2; 20.0 and 10:5 K for R ¼ Tb; Dy and Ho, respectively, and below 2 K (the lowest temperature at the present experiments) for R ¼ Er: The anomalies indicating TN have appeared only in the wc ðTÞ curves, which are the susceptibility when the magnetic field is applied parallel to the c-axis. The N!eel temperature for these compounds is proportional to the de Gennes factors, indicating that the exchange constants for all compounds are originated from the same mechanism. The value of wc decreases abruptly at TN and goes to approximately zero with decreasing temperature. On the other hand, the value of wab ; which is the susceptibility when the external field is in the ab plane, increases smoothly with decreasing temperature without any apparent anomaly. It may be suggested from these behaviors that the magnetic structure for these compounds is a simple antiferromagnetic one with a propagation vector kz ¼ 12; which is not discrepant with the magnetic structure of, for example, NdRhIn5 with k ¼ 12; 0; 12 [3]. The magnetic structure for these
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1021
ARTICLE IN PRESS Y. Isikawa et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 635–636
636
10
1.2
8 M ( µB/ion)
Er
6
H⊥c
H//c H⊥c
2
χ (emu/mol)
ErCoIn5
H //c 4
H⊥c
0.8
HoCoIn5 H //c
RCoIn5
1
DyCoIn5
TbCoIn5
H // c
H⊥ c
H⊥c
H//c 0
0.6 Ho
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7 H (T)
Fig. 2. Magnetization curves of RCoIn5 ðR ¼ Tb; Dy; Ho; ErÞ at 2:0 K: Closed circles denote the magnetization in the field parallel to the c-axis, and open circles in the field perpendicular to the c-axis.
0.4 Dy 0.2
Yb
Tb 0
0
10
20
30
40
50
T (K) Fig. 1. Temperature dependence of the magnetic susceptibility of RCoIn5 ðR ¼ Tb; Dy; Ho; ErÞ: Closed symbols denote the magnetic susceptibility in the field parallel to the c-axis, open symbols in the field perpendicular to the c-axis.
compounds must be determined by neutron-diffraction experiments. Below TN ; multi-step jumps are observed in the magnetization curves, MðHÞ; for R ¼ Dy and Ho in the fields parallel to the axis of easy magnetization, whereas, any jumps in MðHÞ for R ¼ Tb are not observed in the fields up to 7 T as shown in Fig. 2. Saturation magnetization of HoCoIn5 above 5 T reaches approximately the value deduced from the Hund’s rule, and the magnetization for the other compounds is less than the value deduced from the Hund’s rule. This is due to the fact that the TN of HoCoIn5 is the smallest in the present group of RCoIn5 except ErCoIn5 :
The temperature dependence of the magnetic susceptibility above TN up to 300 K for all the compounds except R ¼ Yb has been systematically analyzed by taking into account the effects of the crystalline–electric field and molecular field. The P crystalline-field hamiltonian used here is HCEF ¼ Blm Clm ; where the parameters Blm and Clm are defined in Ref. [4]. Anisotropic magnetic susceptibility for all RCoIn5 ðR ¼ Tb; Dy; Ho; ErÞ is in very good agreement with the calculated ones using only one parameter B20 B130 K for all compounds. Moreover, the anisotropy of the wðTÞ for CeCoIn5 has been analyzed by using approximately the same value of B20 ; although we used an extremely large value of the molecular-field parameter which reflects the Kondo effect.
References [1] [2] [3] [4]
H. Shishido, et al., J. Phys. Soc. Jpn. 71 (2002) 162. T.P. Murphy, et al., Phys. Rev. B 65 (2002) 100514. S. Chang, et al., Phys. Rev. B 66 (2002) 132417. Y. Isikawa, et al., J. Phys. Soc. Jpn. 65 (Suppl.) B (1996) 117.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 635–636
Magnetic properties of single crystals of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ Y. Isikawa*, D. Kato, A. Mitsuda, T. Mizushima, T. Kuwai Department of Physics, Toyama University, Toyama 930-8555, Japan
Abstract The magnetic susceptibility w and magnetization of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ have been investigated using single crystalline samples. The 1=w curves obey the Curie–Weiss law for all compounds except R ¼ Yb: Easy axis of the magnetization is found to be parallel to the c-axis for R ¼ Tb; Dy; Ho; and in the ab plane for R ¼ Er: Below TN ; metamagnetic transitions with multi-step jumps are observed for R ¼ Dy and Ho. The temperature dependence of 1=w curves has been systematically analyzed for all the compounds except R ¼ Yb: r 2003 Elsevier B.V. All rights reserved. PACS: 75.30.Gw Keywords: RCoIn5 ; Single crystal; Magnetic susceptibility; Metamagnetic transition; Easy axis of magnetization
In the heavy fermion superconductor CeCoIn5 [1], a field-induced metamagnetic transition has been observed in the magnetic field applied parallel to the ½1 1 0 direction [2]. This transition appears at 1:4 K and persists to at least 25 K which is much higher than its superconducting transition temperature. It is interesting to compare these behaviors of CeCoIn5 to those of compounds which have not any characters such as Kondo effects. We aim to present the magnetic anisotropy and metamagnetic behaviors of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ: The magnetic susceptibility and magnetization of RCoIn5 ðR ¼ Tb; Dy; Ho; Er; YbÞ have been measured using single crystalline samples which are grown by the In-flux method. These compounds crystallize in the tetragonal crystal structure, and the magnetic atoms R occupy only the corners of the unit cell. The temperature dependence of the magnetic susceptibility w shows the antiferromagnetic behaviors with negative paramagnetic Curie temperatures, and the reciprocal susceptibility obeys the Curie–Weiss law originated from the trivalent rare-earth atoms except *Corresponding author. Tel.: +81-76-445-6583; fax:+81-76445-6549. E-mail address: [email protected] (Y. Isikawa).
R ¼ Yb: As for the exceptional YbCoIn5 ; the value of w is very small, indicating a Pauli paramagnet with divalent Yb atoms. Easy axis of the magnetization is found to be parallel to the c-axis for R ¼ Tb; Dy; Ho; and in the ab plane for R ¼ Er as shown in Fig. 1. The Ne! el temperature, TN ; is 30:2; 20.0 and 10:5 K for R ¼ Tb; Dy and Ho, respectively, and below 2 K (the lowest temperature at the present experiments) for R ¼ Er: The anomalies indicating TN have appeared only in the wc ðTÞ curves, which are the susceptibility when the magnetic field is applied parallel to the c-axis. The N!eel temperature for these compounds is proportional to the de Gennes factors, indicating that the exchange constants for all compounds are originated from the same mechanism. The value of wc decreases abruptly at TN and goes to approximately zero with decreasing temperature. On the other hand, the value of wab ; which is the susceptibility when the external field is in the ab plane, increases smoothly with decreasing temperature without any apparent anomaly. It may be suggested from these behaviors that the magnetic structure for these compounds is a simple antiferromagnetic one with a propagation vector kz ¼ 12; which is not discrepant with the magnetic structure of, for example, NdRhIn5 with k ¼ 12; 0; 12 [3]. The magnetic structure for these
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1021
ARTICLE IN PRESS Y. Isikawa et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 635–636
636
10
1.2
8 M ( µB/ion)
Er
6
H⊥c
H//c H⊥c
2
χ (emu/mol)
ErCoIn5
H //c 4
H⊥c
0.8
HoCoIn5 H //c
RCoIn5
1
DyCoIn5
TbCoIn5
H // c
H⊥ c
H⊥c
H//c 0
0.6 Ho
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7 H (T)
Fig. 2. Magnetization curves of RCoIn5 ðR ¼ Tb; Dy; Ho; ErÞ at 2:0 K: Closed circles denote the magnetization in the field parallel to the c-axis, and open circles in the field perpendicular to the c-axis.
0.4 Dy 0.2
Yb
Tb 0
0
10
20
30
40
50
T (K) Fig. 1. Temperature dependence of the magnetic susceptibility of RCoIn5 ðR ¼ Tb; Dy; Ho; ErÞ: Closed symbols denote the magnetic susceptibility in the field parallel to the c-axis, open symbols in the field perpendicular to the c-axis.
compounds must be determined by neutron-diffraction experiments. Below TN ; multi-step jumps are observed in the magnetization curves, MðHÞ; for R ¼ Dy and Ho in the fields parallel to the axis of easy magnetization, whereas, any jumps in MðHÞ for R ¼ Tb are not observed in the fields up to 7 T as shown in Fig. 2. Saturation magnetization of HoCoIn5 above 5 T reaches approximately the value deduced from the Hund’s rule, and the magnetization for the other compounds is less than the value deduced from the Hund’s rule. This is due to the fact that the TN of HoCoIn5 is the smallest in the present group of RCoIn5 except ErCoIn5 :
The temperature dependence of the magnetic susceptibility above TN up to 300 K for all the compounds except R ¼ Yb has been systematically analyzed by taking into account the effects of the crystalline–electric field and molecular field. The P crystalline-field hamiltonian used here is HCEF ¼ Blm Clm ; where the parameters Blm and Clm are defined in Ref. [4]. Anisotropic magnetic susceptibility for all RCoIn5 ðR ¼ Tb; Dy; Ho; ErÞ is in very good agreement with the calculated ones using only one parameter B20 B130 K for all compounds. Moreover, the anisotropy of the wðTÞ for CeCoIn5 has been analyzed by using approximately the same value of B20 ; although we used an extremely large value of the molecular-field parameter which reflects the Kondo effect.
References [1] [2] [3] [4]
H. Shishido, et al., J. Phys. Soc. Jpn. 71 (2002) 162. T.P. Murphy, et al., Phys. Rev. B 65 (2002) 100514. S. Chang, et al., Phys. Rev. B 66 (2002) 132417. Y. Isikawa, et al., J. Phys. Soc. Jpn. 65 (Suppl.) B (1996) 117.