這篇論文主要是利用核磁共振量測來探討BaCu2V2O8的磁特性，這個化合物主要是屬於一維的鏈系統。BaCu2V2O8這個化合物從磁化率的實驗結果被發現擁有一個很大的大概是230K左右的自旋能隙。也是第一個被發現超過200K的化合物。我們對它的多晶粉末從59K到400K作了核磁共振的量測。BaCu2V2O8中的釩原子在結構中有兩個不同的位置。從這兩個釩原子的奈特位移和自旋晶格鬆弛時間，我們不但證實了這個化合物擁有一個巨大的自旋能隙，同時也發現孤立二聚體模型和交替鏈模型同樣適用於BaCu2V2O8。從奈特位移用交替鏈模型擬合我們可以得到自旋能隙大概是360K。而用孤立二聚體模型則是460K。利用BaCu2V2O8的其中一個位置的釩原子的自旋晶格鬆弛時間資料，我們用交替鏈模型可以得到自旋能隙440K。而用孤立二聚體模型則是450K。我們的結果比磁化率可靠因為核磁共振可以分辨BaCu2V2O8化合物中的Cu雜質對磁化率的影響。

NMR PROBE OF A LARGE SPIN GAP COMPOUND: BaCu2V2O8

(June 2005)

Bing-Xun Xie, B.S., National Chung Cheng University, Taiwan;
Chair of Advisory Committee: Dr. Chin-Shan Lue

This paper concerns with the magnetism of BaCu2V2O8, which is a compound belonging to quasi-one dimensional S=1/2 linear chains systems. It has been discovered that it has a large spin gap about 230K from the data of susceptibility. The first one discovered exceeds 200K in these kinds of compounds and thus is to be noticed. We proposed a 51V NMR study on the polycrystalline powder sample and carried out through a temperature from 59 K to 400 K. The analysis of the Knight shift and the spin-lattice relaxation time applied on the two Vanadium sites of BaCu2V2O8 not only confirmed the existence of a large spin gap but also showed that both the isolated dimmer model and alternating chain model are suitable for BaCu2V2O8. The Knight shift fitted by alternating dimer model gave spin gap energy about 360K. Also, the Knight shift could fit by isolated model and gave the spin gap about 460K. The relaxation time of V-II site (one of site V sites in BaCu2V2O8) fitted by alternating and dimer model gave the spin gap 440K and 450K separately. Our result is more reliable since the NMR can not see the Cu impurities which contribute a tail in the low temperature in measurement of susceptibility.

1. M. Hase, I. Terasaki, and K.Uchinokura, Phys. Rev. Lett. 70, 3651 (1993).
2. M. Nishi, O. Fujita, J. Akimitsu, Phys. Rev. B 50, 6508 (1994).
3. M. Hase, I. Terasaki, Y. Sasago, and K. Uchinokura, Phys. Rev. Lett. 71, 4059 (1993).
4. P. H. M. van Loosdrecht, J. P. Boucher, and G. Martinez, G. Dhalenne and A. Revcolevschi, Phys. Rev. Lett. 76, 311 (1996).
5. S. B. Oseroff, S-W. Cheong, B. Aktas, M. F. Hundley, Z. Fisk, and L. W. Rupp, Jr. Phys. Rev. Lett. 74, 1450 (1995).
6. Götz S. Uhrig, Phys. Rev. Lett. 79, 163 (1997).
7. B. Grenier, J. P. Renard, P. Veillet, C. Paulsen, G. Dhalenne, and A. Revcolevschi, Phys. Rev. B 58, 8202 (1998).
8. P. E. Anderson, J. Z. Liu, and R. N. Shelton, Phys. Rev. B 56, 11014 (1997).
9. M. Weiden, R. Hauptmann, W. Richter, C. Geibel, P. Hellmann, M. Köppen, F. Steglich, M. Fischer, P. Lemmens, G. Güntherodt, A. Krimmel, and G. Nieva, Phys. Rev. B 55, 15067 (1997).
10. B. Grenier, J. P. Renard, P. Veillet, C. Paulsen, R. Calemczuk, G. Dhalenne, and A. Revcolevschi, Phys. Rev. B 57, 3444 (1997).
11. A. W. Garrnett, S. E. Nagler, D. A. Tennant, B. C. Sales, and T. Barnes, Phys. Rev. Lett. 79, 745 (1997).
12. Z. Hiroi, M. Azuma, Y. Fujishiro, T. Saito, M. Takano, F. Izumi, T. Kamiyama, and T. Ikeda, J. Solid State Chem. 146, 369 (1999).
13. J. Kikuchi, K. Motoya, T. Yamauchi, and Y. Ueda, Phys. Rev. B 60, 6731 (1999).
14. M. Azuma, T. Saito, Y. Fujishiro, Z. Hiroi, M. Takano, F. Izumi, T. Kamiyama, T. Ikeda, Y. Narumi, and K. Kindo, Phys. Rev. B 60, 10145 (1999).
15. A. N. Vasil'ev, M. M. Markina, and E. A. Popova, Low Temperature Physics, 31, 203 (2005)
16. R. Vogt and Hk. Müller-Buschbaum, Z. Anorg,. Allg. Chem. 591, 167 (1990).
17. Z. He, T. Kyômen, M. Itoh. Phys. Rev. B 69, 220407 (2004).
18. N. Majlis, Quantum Theory of Magnetism (World Science, Singapore, 2000).
19. U. Schollwöck, J. Richter, D. J. J. Farnell, R. F. Bishop, (Eds.) Quantum Magnetism (Springer, Germany, 2004) and reference therein.
20. P. Lemmens, G. Guntherodt, and C. Gros, phys. Rep. 375, 1 (2003), and references therein.
21. H. A. Bethe, Z. Physik., 71, 205 (1931)
22. T. Barnes, J. Riera, and D. A. Tennant, Phys. Rev. B. 59, 11384 (1999).
23. M. Troyer, H, Tsunetsugu, and D. Wurtz, Phys. Rev. B 50, 13515 (1994).
24. G. C. Carter, L. H. Betnnett, and D. J. Kahan, Mettallic Shifts in NMR (Pergamon, Oxford, 1977).
25. C. P. Sliter, Principles of Magnetic Resonance (Springer-Verlag, New York, 1990).
26. A. Abragem, Principle of Magnetic Resonance (Oxford University Press, London, 1982).
27. E. Fukushima and S. B. W. Roeder, Experimental Pulse NMR (Addison-Wesley, Reading MA, 1981).
28. F. Bloch, Phys. Rev. 70, 460 (1946)
29. W. W. Simons, W. J. O’Sullivan, and W. A. Robinson, Phys. Rev. 127, 1168
(1962)