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High-pressure synthesis of Yb2Cu2In and its physical properties
Journal of Alloys and Compounds 322 (2001) 74–76
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www.elsevier.com / locate / jallcom
High-pressure synthesis of Yb 2 Cu 2 In and its physical properties N. Tsujii a , *, H. Kitoˆ b , H. Kitazawa a , G. Kido a a
b
National Institute for Material Science, Sengen 1 -2 -1, Tsukuba, Ibaraki 305 -0047, Japan Electrotechnical Laboratory, National Institute of Advanced Industrial and Technology, Umezono 1 -1 -4, Tsukuba, Ibaraki 305 -8568, Japan Received 26 February 2001; accepted 5 March 2001
Abstract The Yb 2 Cu 2 In compound with the tetragonal Mo 2 B 2 Fe structure has been prepared using a high-pressure technique. The lattice volume is found to be considerably larger than that expected for the system with usual Yb 31 configuration. The temperature dependence of the magnetic susceptibility and the electrical resistivity shows that this system is almost non-magnetic. These results indicate that the Yb ion in this system is very close to the divalent state. 2001 Elsevier Science B.V. All rights reserved. Keywords: Rare earth compounds; Synthesis, Electrical transport; Magnetic measurements
1. Introduction Recently, a large number of compounds with the formula, R 2 M 2 X (R5rare earth, M5transition metal, X5 Al, In, etc.), have been reported. Some of them show quite interesting phenomena related to heavy-fermion physics [1], complicated magnetic properties [2], and so on. Kalychak et al. have reported that the R 2 Cu 2 In compounds with R5La–Tm and Lu have the tetragonal Mo 2 B 2 Fe structure (space group P4 /mbm) [3], which is derived from the U 3 Si 2 -type structure by replacing one U-site atom by an Fe atom. Fisher et al. have prepared single crystals of R 2 Cu 2 In with R5Gd–Tm and Lu, and have reported ferromagnetic behavior of these compounds, except for Lu, with relatively high Curie-temperatures [4]. The existence of Yb 2 Cu 2 In has, however, not been reported in spite of the existence of Tm 2 Cu 2 In and Lu 2 Cu 2 In. We have indeed confirmed the absence of the Yb 2 Cu 2 In compound at ambient pressure by direct melting of stoichiometric metals. This may be due to the preference of Yb for the divalent state, since the Yb 21 ion has a much larger radius than that of R31 (Gd–Lu). Yb 2 Cu 2 In may hence be stabilized under high pressure, where the smaller Yb 31 state is stable rather than the larger Yb 21 one. Such a case is actually reported for the cubic RCu 5 compounds [5]. In this paper, we report the high-pressure synthesis of *Corresponding author. Tel.: 181-298-59-2817; fax: 181-298-592801. E-mail address: [email protected] (N. Tsujii).
the Mo 2 B 2 Fe-type Yb 2 Cu 2 In compound, and its magnetic and electric properties. We show the procedure of the sample preparation in Section 2, and show the results of experiments in Section 3.
2. Experimental The polycrystalline sample of Yb 2 Cu 2 In has been prepared in two steps. First, pure elements of Yb (99.9%), Cu (99.99%), In (99.999%) were inserted into a BN crucible. A slight excess of Yb was used to compensate the loss due to the high volatile pressure of Yb. They were sealed in an evacuated silica tube, heated up to 11508C for 30 min at ambient pressure, and quenched into water. The tube was subsequently annealed at 5008C for 3 days. The product was found to be composed of several phases without the Mo 2 B 2 Fe-type. After that, the ingot was placed into a BN cell, heated under the pressure of 3.5 GPa at 6008C for 2 h. The high-pressure was generated by a cubic anvil apparatus (Riken CAP-07). The cell was heated using a graphite heater. The temperature under pressure was estimated from the input power using a calibrated curve. The sample was rapidly cooled to room temperature before the pressure was released. Powder Xray diffraction was measured to check the structure of the sample. Magnetic susceptibility was measured in a field of 0.1 Tesla using a superconducting quantum interference device (SQUID) magnetometer (Quantum Design,
0925-8388 / 01 / $ – see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 01 )01261-0
N. Tsujii et al. / Journal of Alloys and Compounds 322 (2001) 74 – 76
75
MPMS5). Electrical resistivity measurement was performed by a dc four-probe method.
3. Results and discussion Fig. 1 shows the powder X-ray diffraction (XRD) pattern of the high-pressure synthesized Yb 2 Cu 2 In sample. The pattern is well explained with the calculated pattern based on the Mo 2 B 2 Fe-type structure. The lattice parame˚ and c53.892 A ˚ using ters are estimated to be a57.473 A the 2u value of the diffraction peaks from the (410), (411), (331), (312), and (511) plane. The calculated pattern was obtained using the RIETAN program [6]. In Fig. 2, the lattice volume of Yb 2 Cu 2 In is plotted together with those of R 2 Cu 2 In (R5Gd–Tm, Lu) reported by Kalychak et al. [3]. One finds that the lattice parameters of R 2 Cu 2 In (R5Gd–Tm, Lu) decrease monotonically with increasing atomic number. The lattice parameter of Yb 2 Cu 2 In is however substantially larger than those for the other compounds. This fact suggests that the Yb valence is divalent or very close to divalent. The magnetic susceptibility was measured in order to investigate the valence state of the Yb 2 Cu 2 In system. The result is shown in Fig. 3. The susceptibility shows very small values and is less temperature dependent around 100–300 K. One can find a small anomaly at T545 K, likely to be due to an oxygen-related transition. We hence conclude that Yb 2 Cu 2 In does not order magnetically down to 2 K. We have attempted to fit the susceptibility in the temperature between 150 and 300 K by a Curie–Weiss function, x (T ) 5 C /(T 2 u ) 1 x0 , where C, u, x0 are the Curie constant, Weiss-temperature, and the temperature independent susceptibility, respectively. The fitting yields the value C50.162 emu / Yb-mol K, u 5 230.4 K, and
Fig. 2. Unit cell volumes of the R 2 Cu 2 In compounds. The data except for Yb are referred to [3].
x0 55.13310 24 emu / Yb-mol. One the other hand, the theoretical value of the Curie constant for Yb 31 ion is C52.58 emu / Yb-mol K, since the Bohr magneton of a Yb 31 ion should be 4.54 m B . This result indicates that the valence of Yb in Yb 2 Cu 2 In is very close to the nonmagnetic divalent state, consistent with the lattice parameter anomaly mentioned above. Fig. 4 shows the temperature dependence of electrical resistivity of Yb 2 Cu 2 In. The resistivity is metallic, decreasing monotonically with decreasing temperature. No anomaly is observed in the whole temperature range measured, consistent with the paramagnetic behavior suggested from the magnetic susceptibility. In conclusion, we have successfully synthesized the polycrystalline Yb 2 Cu 2 In compound with Mo 2 B 2 Fe-type
Fig. 1. (a) Powder X-ray diffraction pattern of Yb 2 Cu 2 In compound prepared by the high-pressure technique. Peaks marked by m are assigned to extrinsic ˚ and c53.895 A. ˚ phases. (b) Calculated diffraction pattern for the Mo 2 B 2 Fe-type structure with lattice constants of a57.473 A
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N. Tsujii et al. / Journal of Alloys and Compounds 322 (2001) 74 – 76
structure by a high-pressure technique. The lattice parameter was found to be larger than those of R 2 Cu 2 In (R5Gd– Tm, Lu), indicating nearly divalent state of the Yb ion. Magnetic order is found to be absent down to 2 K unlike other R 2 Cu 2 In compounds, which show ferromagnetic order at relatively high temperatures. This discrepancy is attributed to the non-magnetic Yb 21 state. Applying further high-pressure may be useful to obtain the Yb 2 Cu 2 In compound with magnetic Yb 31 ions. It should be stressed that high-pressure techniques are quite powerful to search new Yb-based intermetallics.
References
Fig. 3. Magnetic susceptibility of Yb 2 Cu 2 In. The solid line represents the result of a Curie–Weiss fitting.
Fig. 4. Electrical resistivity of Yb 2 Cu 2 In.
[1] D. Kaczorowski, R. Rogl, K. Hiebl, Phys. Rev. B 54 (1996) 9891. [2] F. Canepa, S. Cirafici, F. Merlo, M. Pani, C. Ferdeghini, J. Magn. Magn. Mater. 195 (1999) 646. [3] Ya.M. Kalychak, V.I. Zaremba, V.M. Baranyak, P.Yu. Zavalii, V.A. Bruskov, L.V. Sysa, O.V. Dmytrakh, Inorg. Mater. 26 (1990) 74. [4] I.R. Fisher, Z. Islam, P.C. Canfield, J. Magn. Magn. Mater. 202 (1999) 1. [5] J. He, N. Tsujii, M. Nakanishi, K. Yoshimura, K. Kosuge, J. Alloys Comp. 240 (1996) 261. [6] Chapter 13 F. Izumi, in: R.A. Young (Ed.), The Rietveld Method, Oxford University Press, Oxford, 1993.
L
www.elsevier.com / locate / jallcom
High-pressure synthesis of Yb 2 Cu 2 In and its physical properties N. Tsujii a , *, H. Kitoˆ b , H. Kitazawa a , G. Kido a a
b
National Institute for Material Science, Sengen 1 -2 -1, Tsukuba, Ibaraki 305 -0047, Japan Electrotechnical Laboratory, National Institute of Advanced Industrial and Technology, Umezono 1 -1 -4, Tsukuba, Ibaraki 305 -8568, Japan Received 26 February 2001; accepted 5 March 2001
Abstract The Yb 2 Cu 2 In compound with the tetragonal Mo 2 B 2 Fe structure has been prepared using a high-pressure technique. The lattice volume is found to be considerably larger than that expected for the system with usual Yb 31 configuration. The temperature dependence of the magnetic susceptibility and the electrical resistivity shows that this system is almost non-magnetic. These results indicate that the Yb ion in this system is very close to the divalent state. 2001 Elsevier Science B.V. All rights reserved. Keywords: Rare earth compounds; Synthesis, Electrical transport; Magnetic measurements
1. Introduction Recently, a large number of compounds with the formula, R 2 M 2 X (R5rare earth, M5transition metal, X5 Al, In, etc.), have been reported. Some of them show quite interesting phenomena related to heavy-fermion physics [1], complicated magnetic properties [2], and so on. Kalychak et al. have reported that the R 2 Cu 2 In compounds with R5La–Tm and Lu have the tetragonal Mo 2 B 2 Fe structure (space group P4 /mbm) [3], which is derived from the U 3 Si 2 -type structure by replacing one U-site atom by an Fe atom. Fisher et al. have prepared single crystals of R 2 Cu 2 In with R5Gd–Tm and Lu, and have reported ferromagnetic behavior of these compounds, except for Lu, with relatively high Curie-temperatures [4]. The existence of Yb 2 Cu 2 In has, however, not been reported in spite of the existence of Tm 2 Cu 2 In and Lu 2 Cu 2 In. We have indeed confirmed the absence of the Yb 2 Cu 2 In compound at ambient pressure by direct melting of stoichiometric metals. This may be due to the preference of Yb for the divalent state, since the Yb 21 ion has a much larger radius than that of R31 (Gd–Lu). Yb 2 Cu 2 In may hence be stabilized under high pressure, where the smaller Yb 31 state is stable rather than the larger Yb 21 one. Such a case is actually reported for the cubic RCu 5 compounds [5]. In this paper, we report the high-pressure synthesis of *Corresponding author. Tel.: 181-298-59-2817; fax: 181-298-592801. E-mail address: [email protected] (N. Tsujii).
the Mo 2 B 2 Fe-type Yb 2 Cu 2 In compound, and its magnetic and electric properties. We show the procedure of the sample preparation in Section 2, and show the results of experiments in Section 3.
2. Experimental The polycrystalline sample of Yb 2 Cu 2 In has been prepared in two steps. First, pure elements of Yb (99.9%), Cu (99.99%), In (99.999%) were inserted into a BN crucible. A slight excess of Yb was used to compensate the loss due to the high volatile pressure of Yb. They were sealed in an evacuated silica tube, heated up to 11508C for 30 min at ambient pressure, and quenched into water. The tube was subsequently annealed at 5008C for 3 days. The product was found to be composed of several phases without the Mo 2 B 2 Fe-type. After that, the ingot was placed into a BN cell, heated under the pressure of 3.5 GPa at 6008C for 2 h. The high-pressure was generated by a cubic anvil apparatus (Riken CAP-07). The cell was heated using a graphite heater. The temperature under pressure was estimated from the input power using a calibrated curve. The sample was rapidly cooled to room temperature before the pressure was released. Powder Xray diffraction was measured to check the structure of the sample. Magnetic susceptibility was measured in a field of 0.1 Tesla using a superconducting quantum interference device (SQUID) magnetometer (Quantum Design,
0925-8388 / 01 / $ – see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 01 )01261-0
N. Tsujii et al. / Journal of Alloys and Compounds 322 (2001) 74 – 76
75
MPMS5). Electrical resistivity measurement was performed by a dc four-probe method.
3. Results and discussion Fig. 1 shows the powder X-ray diffraction (XRD) pattern of the high-pressure synthesized Yb 2 Cu 2 In sample. The pattern is well explained with the calculated pattern based on the Mo 2 B 2 Fe-type structure. The lattice parame˚ and c53.892 A ˚ using ters are estimated to be a57.473 A the 2u value of the diffraction peaks from the (410), (411), (331), (312), and (511) plane. The calculated pattern was obtained using the RIETAN program [6]. In Fig. 2, the lattice volume of Yb 2 Cu 2 In is plotted together with those of R 2 Cu 2 In (R5Gd–Tm, Lu) reported by Kalychak et al. [3]. One finds that the lattice parameters of R 2 Cu 2 In (R5Gd–Tm, Lu) decrease monotonically with increasing atomic number. The lattice parameter of Yb 2 Cu 2 In is however substantially larger than those for the other compounds. This fact suggests that the Yb valence is divalent or very close to divalent. The magnetic susceptibility was measured in order to investigate the valence state of the Yb 2 Cu 2 In system. The result is shown in Fig. 3. The susceptibility shows very small values and is less temperature dependent around 100–300 K. One can find a small anomaly at T545 K, likely to be due to an oxygen-related transition. We hence conclude that Yb 2 Cu 2 In does not order magnetically down to 2 K. We have attempted to fit the susceptibility in the temperature between 150 and 300 K by a Curie–Weiss function, x (T ) 5 C /(T 2 u ) 1 x0 , where C, u, x0 are the Curie constant, Weiss-temperature, and the temperature independent susceptibility, respectively. The fitting yields the value C50.162 emu / Yb-mol K, u 5 230.4 K, and
Fig. 2. Unit cell volumes of the R 2 Cu 2 In compounds. The data except for Yb are referred to [3].
x0 55.13310 24 emu / Yb-mol. One the other hand, the theoretical value of the Curie constant for Yb 31 ion is C52.58 emu / Yb-mol K, since the Bohr magneton of a Yb 31 ion should be 4.54 m B . This result indicates that the valence of Yb in Yb 2 Cu 2 In is very close to the nonmagnetic divalent state, consistent with the lattice parameter anomaly mentioned above. Fig. 4 shows the temperature dependence of electrical resistivity of Yb 2 Cu 2 In. The resistivity is metallic, decreasing monotonically with decreasing temperature. No anomaly is observed in the whole temperature range measured, consistent with the paramagnetic behavior suggested from the magnetic susceptibility. In conclusion, we have successfully synthesized the polycrystalline Yb 2 Cu 2 In compound with Mo 2 B 2 Fe-type
Fig. 1. (a) Powder X-ray diffraction pattern of Yb 2 Cu 2 In compound prepared by the high-pressure technique. Peaks marked by m are assigned to extrinsic ˚ and c53.895 A. ˚ phases. (b) Calculated diffraction pattern for the Mo 2 B 2 Fe-type structure with lattice constants of a57.473 A
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N. Tsujii et al. / Journal of Alloys and Compounds 322 (2001) 74 – 76
structure by a high-pressure technique. The lattice parameter was found to be larger than those of R 2 Cu 2 In (R5Gd– Tm, Lu), indicating nearly divalent state of the Yb ion. Magnetic order is found to be absent down to 2 K unlike other R 2 Cu 2 In compounds, which show ferromagnetic order at relatively high temperatures. This discrepancy is attributed to the non-magnetic Yb 21 state. Applying further high-pressure may be useful to obtain the Yb 2 Cu 2 In compound with magnetic Yb 31 ions. It should be stressed that high-pressure techniques are quite powerful to search new Yb-based intermetallics.
References
Fig. 3. Magnetic susceptibility of Yb 2 Cu 2 In. The solid line represents the result of a Curie–Weiss fitting.
Fig. 4. Electrical resistivity of Yb 2 Cu 2 In.
[1] D. Kaczorowski, R. Rogl, K. Hiebl, Phys. Rev. B 54 (1996) 9891. [2] F. Canepa, S. Cirafici, F. Merlo, M. Pani, C. Ferdeghini, J. Magn. Magn. Mater. 195 (1999) 646. [3] Ya.M. Kalychak, V.I. Zaremba, V.M. Baranyak, P.Yu. Zavalii, V.A. Bruskov, L.V. Sysa, O.V. Dmytrakh, Inorg. Mater. 26 (1990) 74. [4] I.R. Fisher, Z. Islam, P.C. Canfield, J. Magn. Magn. Mater. 202 (1999) 1. [5] J. He, N. Tsujii, M. Nakanishi, K. Yoshimura, K. Kosuge, J. Alloys Comp. 240 (1996) 261. [6] Chapter 13 F. Izumi, in: R.A. Young (Ed.), The Rietveld Method, Oxford University Press, Oxford, 1993.