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149Sm nuclear resonant scattering of SmB2C2
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 199–200
149
Sm nuclear resonant scattering of SmB2C2
Satoshi Tsutsuia,*, Yasuhiro Kobayashib, Yoshitaka Yodaa, Makoto Setob, Kentaro Indohc, Hideya Onoderac a
Materials Science Division, Japan Synchrotron Radiation Research Institute (SPring-8), Mikazuki, Hyogo 679-5198, Japan b Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan c Institute for Meterials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
Abstract The quantum beat spectra due to magnetic ordering can be observed below the 51 K upper transition temperature of SmB2C2 using the nuclear resonant forward scattering technique with the 149Sm nuclei. The spectrum without dynamical or quantum beats can be observed at 60 K. This result indicates that the magnetic interaction continues to exist above 51 K. Examinations of the diffuse magnetic scattering of neutrons from HoB2C2 show a similar continuation of the magnetic interaction above the N!eel temperature. It appears that the spectrum at 60 K is caused by a distribution of the hyperfine magnetic field. r 2003 Elsevier B.V. All rights reserved. PACS: 76.30.kg; 76.80.ty; 77.22.Ej Keywords: SmB2C2; Nuclear resonant scattering; Hyperfine magnetic field
1. Introduction SmB2C2 has two transition temperatures of 51 and 37 K [1]. The temperature dependence of the magnetic susceptibility behaves antiferromagnetically at each transition temperature. The entropy at 51 K approaches R ln 2. This fact suggests that these two transition temperatures are caused by antiferromagnetic ordering. Nuclear resonant scattering (NRS) is a powerful tool for investigating magnetic properties [2]. The NRS technique is one of the applications of the M.ossbauer effect. This technique needs a high-resolution monochro. mator, whereas conventional Mossbauer spectroscopy (MS) needs a radioactive source. In NRS spectra using forward scattering, two kinds of beats can be observed. One is a dynamical beat that depends on the effective thickness of a sample; the other is a quantum beat that depends on the hyperfine interaction at probe nucleus. 149 Sm MS is more useful for investigating the magnetic properties in Sm compounds than neutron *Corresponding author. Tel.: +81-791-58-0802; fax: +81791-58-0830. E-mail address: [email protected] (S. Tsutsui).
scattering because Sm is a good absorber for neutrons. Since the radioactive source 149Eu for 149Sm conventional MS is hard to prepare, we have performed 149Sm NRS to investigate the magnetic properties of SmB2C2. In the present work, the quantum beat due to magnetic ordering can be observed at 6 and 40 K in SmB2C2. In addition, the distribution of the hyperfine magnetic field can be observed at 60 K using an NRS technique.
2. Experimental setup The experiment was carried out at BL09XU at SPring-8. The energy used is 22.507 keV, the resonant energy of the 149Sm nucleus. The high-resolution monochrometer consists of Si(4 4 0), Si(16 8 8) and Ge(4 2 2) [3]. The resolution of this monochrometer is 1.5 meV, which was measured by comparison with the 149 Sm resonance in 149Sm2O3. The bunch mode contains 203 bunches separated by 23.6 ns, more than the lifetime of the 149Sm nucleus, 10.27 ns. The detector is an avalanche photodiode (APD) [4]. The measured sample is a single crystal [1]. The thickness of the sample is about 500 mm. The sample is
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.11.077
ARTICLE IN PRESS S. Tsutsui et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 199–200
200
put in a He-flow cryostat. The direction of the incident X-ray beam is parallel to the [0 0 1] direction on the sample. The experimental setup is a forward scattering geometry.
3. Results and discussion Fig. 1 shows the NRS spectra of SmB2C2 at 300, 60, 40 and 6 K. The spectrum at 300 K mainly consists of a dynamical beat due to the effective thickness of the sample, whereas the spectra at 40 and 6 K consist of both a dynamical beat and quantum beat due mainly to the hyperfine magnetic field at the 149Sm nucleus. This result indicates that both transition temperatures are set by the magnetic order, indicated by the cusps in the measurement of specific heat as a function of temperature [1]. On the other hand, neither dynamical nor quantum beats can be observed in the spectrum at 60 K. According to the result of the magnetic susceptibility measurements, SmB2C2 is a paramagnet above 51 K [1]. The spectrum at 60 K is characteristic of a spectrum with
a distribution of the hyperfine interaction or with a relaxation phenomenon, because the decay at 60 K is faster than the decay expected in the lifetime of 149Sm, 10.27 ns. This result suggests that the magnetic interaction in SmB2C2 remains even at 60 K. Similar results have already been reported in DyB2C2 and HoB2C2, whose crystal structure is the same as that of SmB2C2. The magnetic relaxation is 161 Dy; MS was observed not only in the antiferroquadrupole ordered state but also in the paramagnetic state of DyB2C2 [5]. The magnetic diffuse scattering can be observed above the N!eel temperature of HoB2C2 with neutrons [6]. The short-range magnetic interaction thus appears to exist above the Ne! el temperature in these compounds. The phenomenon observed in SmB2C2 is certainly a similar behavior to that of DyB2C2, but our recent measurements of the electronic resonant scattering indicate that the magnetic structure of SmB2C2 is similar to that of HoB2C2 in both of the magnetically ordered phases [6,7]. This suggests that the spectrum at 60 K is due to the distribution of the hyperfine magnetic field.
4. Summary SmB2C2 4
10
300 K 2
10
The quantum beat due to the magnetic ordering can clearly be observed at 40 and 6 K in SmB2C2 using a 149 Sm NRS technique. The spectrum at 60 K suggests that the distributed hyperfine magnetic field is observed at the 149Sm nuclei. This is correlated with the magnetic diffuse scattering like that in HoB2C2 using the neutron scattering.
0
Intensity (Arb. Units)
10 4 10
Acknowledgements 60 K
The authors thank Dr. A.Q.R. Baron for the support on the APD detector. This work was performed at the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2002A0203ND3-np).
2
10
0
10 4 10 40 K
References
2
10
0
10 4 10
6K
2
10
0
10
Fig. 1.
5 149
10 15 Time (nsec)
20
Sm NRS spectra of SmB2C2 at 300, 60, 40 and 6 K.
[1] K. Indoh, H. Onodera, Y. Yamaguchi, Physica B 312–313 (2002) 318. [2] E. Gerdau, H. de Waard (Eds.), Nuclear Resonant Scattering of Synchrotron Radiation (Part A), Hyperfine Interactions, 123/124, 2000 and references therein. [3] Y. Yoda, Private communication. [4] A.Q.R. Baron, Hyperfine Interactions 125 (2000) 29. [5] K. Indoh, H. Onodera, H. Yamauchi, H. Kobayashi, Y. Yamaguchi, J. Phys. Soc. Japan 69 (2000) 1978. [6] K. Ohoyama, H. Yamauchi, A. Tobo, H. Onodera, H. Kadowaki, Y. Yamaguchi, J. Phys. Soc. Japan 3401 (2000) 69. [7] T. Inami, T. Honma, S. Tsutsui, K. Indoh, H. Onodera, et al. unpublished.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 199–200
149
Sm nuclear resonant scattering of SmB2C2
Satoshi Tsutsuia,*, Yasuhiro Kobayashib, Yoshitaka Yodaa, Makoto Setob, Kentaro Indohc, Hideya Onoderac a
Materials Science Division, Japan Synchrotron Radiation Research Institute (SPring-8), Mikazuki, Hyogo 679-5198, Japan b Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan c Institute for Meterials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
Abstract The quantum beat spectra due to magnetic ordering can be observed below the 51 K upper transition temperature of SmB2C2 using the nuclear resonant forward scattering technique with the 149Sm nuclei. The spectrum without dynamical or quantum beats can be observed at 60 K. This result indicates that the magnetic interaction continues to exist above 51 K. Examinations of the diffuse magnetic scattering of neutrons from HoB2C2 show a similar continuation of the magnetic interaction above the N!eel temperature. It appears that the spectrum at 60 K is caused by a distribution of the hyperfine magnetic field. r 2003 Elsevier B.V. All rights reserved. PACS: 76.30.kg; 76.80.ty; 77.22.Ej Keywords: SmB2C2; Nuclear resonant scattering; Hyperfine magnetic field
1. Introduction SmB2C2 has two transition temperatures of 51 and 37 K [1]. The temperature dependence of the magnetic susceptibility behaves antiferromagnetically at each transition temperature. The entropy at 51 K approaches R ln 2. This fact suggests that these two transition temperatures are caused by antiferromagnetic ordering. Nuclear resonant scattering (NRS) is a powerful tool for investigating magnetic properties [2]. The NRS technique is one of the applications of the M.ossbauer effect. This technique needs a high-resolution monochro. mator, whereas conventional Mossbauer spectroscopy (MS) needs a radioactive source. In NRS spectra using forward scattering, two kinds of beats can be observed. One is a dynamical beat that depends on the effective thickness of a sample; the other is a quantum beat that depends on the hyperfine interaction at probe nucleus. 149 Sm MS is more useful for investigating the magnetic properties in Sm compounds than neutron *Corresponding author. Tel.: +81-791-58-0802; fax: +81791-58-0830. E-mail address: [email protected] (S. Tsutsui).
scattering because Sm is a good absorber for neutrons. Since the radioactive source 149Eu for 149Sm conventional MS is hard to prepare, we have performed 149Sm NRS to investigate the magnetic properties of SmB2C2. In the present work, the quantum beat due to magnetic ordering can be observed at 6 and 40 K in SmB2C2. In addition, the distribution of the hyperfine magnetic field can be observed at 60 K using an NRS technique.
2. Experimental setup The experiment was carried out at BL09XU at SPring-8. The energy used is 22.507 keV, the resonant energy of the 149Sm nucleus. The high-resolution monochrometer consists of Si(4 4 0), Si(16 8 8) and Ge(4 2 2) [3]. The resolution of this monochrometer is 1.5 meV, which was measured by comparison with the 149 Sm resonance in 149Sm2O3. The bunch mode contains 203 bunches separated by 23.6 ns, more than the lifetime of the 149Sm nucleus, 10.27 ns. The detector is an avalanche photodiode (APD) [4]. The measured sample is a single crystal [1]. The thickness of the sample is about 500 mm. The sample is
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.11.077
ARTICLE IN PRESS S. Tsutsui et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 199–200
200
put in a He-flow cryostat. The direction of the incident X-ray beam is parallel to the [0 0 1] direction on the sample. The experimental setup is a forward scattering geometry.
3. Results and discussion Fig. 1 shows the NRS spectra of SmB2C2 at 300, 60, 40 and 6 K. The spectrum at 300 K mainly consists of a dynamical beat due to the effective thickness of the sample, whereas the spectra at 40 and 6 K consist of both a dynamical beat and quantum beat due mainly to the hyperfine magnetic field at the 149Sm nucleus. This result indicates that both transition temperatures are set by the magnetic order, indicated by the cusps in the measurement of specific heat as a function of temperature [1]. On the other hand, neither dynamical nor quantum beats can be observed in the spectrum at 60 K. According to the result of the magnetic susceptibility measurements, SmB2C2 is a paramagnet above 51 K [1]. The spectrum at 60 K is characteristic of a spectrum with
a distribution of the hyperfine interaction or with a relaxation phenomenon, because the decay at 60 K is faster than the decay expected in the lifetime of 149Sm, 10.27 ns. This result suggests that the magnetic interaction in SmB2C2 remains even at 60 K. Similar results have already been reported in DyB2C2 and HoB2C2, whose crystal structure is the same as that of SmB2C2. The magnetic relaxation is 161 Dy; MS was observed not only in the antiferroquadrupole ordered state but also in the paramagnetic state of DyB2C2 [5]. The magnetic diffuse scattering can be observed above the N!eel temperature of HoB2C2 with neutrons [6]. The short-range magnetic interaction thus appears to exist above the Ne! el temperature in these compounds. The phenomenon observed in SmB2C2 is certainly a similar behavior to that of DyB2C2, but our recent measurements of the electronic resonant scattering indicate that the magnetic structure of SmB2C2 is similar to that of HoB2C2 in both of the magnetically ordered phases [6,7]. This suggests that the spectrum at 60 K is due to the distribution of the hyperfine magnetic field.
4. Summary SmB2C2 4
10
300 K 2
10
The quantum beat due to the magnetic ordering can clearly be observed at 40 and 6 K in SmB2C2 using a 149 Sm NRS technique. The spectrum at 60 K suggests that the distributed hyperfine magnetic field is observed at the 149Sm nuclei. This is correlated with the magnetic diffuse scattering like that in HoB2C2 using the neutron scattering.
0
Intensity (Arb. Units)
10 4 10
Acknowledgements 60 K
The authors thank Dr. A.Q.R. Baron for the support on the APD detector. This work was performed at the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2002A0203ND3-np).
2
10
0
10 4 10 40 K
References
2
10
0
10 4 10
6K
2
10
0
10
Fig. 1.
5 149
10 15 Time (nsec)
20
Sm NRS spectra of SmB2C2 at 300, 60, 40 and 6 K.
[1] K. Indoh, H. Onodera, Y. Yamaguchi, Physica B 312–313 (2002) 318. [2] E. Gerdau, H. de Waard (Eds.), Nuclear Resonant Scattering of Synchrotron Radiation (Part A), Hyperfine Interactions, 123/124, 2000 and references therein. [3] Y. Yoda, Private communication. [4] A.Q.R. Baron, Hyperfine Interactions 125 (2000) 29. [5] K. Indoh, H. Onodera, H. Yamauchi, H. Kobayashi, Y. Yamaguchi, J. Phys. Soc. Japan 69 (2000) 1978. [6] K. Ohoyama, H. Yamauchi, A. Tobo, H. Onodera, H. Kadowaki, Y. Yamaguchi, J. Phys. Soc. Japan 3401 (2000) 69. [7] T. Inami, T. Honma, S. Tsutsui, K. Indoh, H. Onodera, et al. unpublished.