臺灣博碩士論文加值系統

在這份論文之中，我們製作了含稀土元素之合金 (R2NiGe3，R = Y、La、Ce、Pr、Nd、Sm、Gd、Dy、Ho)並成功地量測其結構與電磁性質。經由X-ray繞射結構分析，除了Sm的樣品為純相之外，其餘樣品之結構在靠近(101)處，含有一個來自於化學劑量比例為1:2:2的相，除此之外並無其它的額外多餘的相，因此我們相信其結構應為六角最密堆積的AlB2 結構。對於Y2NiGe3與La2NiGe3這兩個樣品，根據電阻率的資料顯示，在溫度低於1 K時，它們應該是超導體。而 Gd2NiGe3 與Dy2NiGe3則在低溫的時候，具有反鐵磁的特性。在電性方面，Ce2NiGe3這個樣品在低溫時(6 K~18 K)其電阻隨溫度下降而上升，而其電阻來自於磁性的部份，在300 K到80 K 隨溫度下降而上升，在低於6 K後，隨溫度下降而下降，這樣的行為與近藤晶格系統 (Kondo lattice system) 類似。

We have successfully synthesized the rare earth ternary intermetallics R2NiGe3 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Dy, and Ho), which crystallized in a AlB2-derived hexagonal structure with space group P6/mmm as confirmed from the X-ray diffraction measurements. Except Sm2NiGe3, all the samples have additional peak which is due to a parasitic phase with the stoichiometry 1:2:2.
Magnetic behavior and electrical resistivity are investigated on this compound. Curie-Weiss law is used to calculate the effective moments of the rare earth ions in the paramagnetic state. The magnetization measurements indicate that Y2NiGe3 and La2NiGe3 are not superconductors above 2 K, and the R2NiGe3 compounds (R = Gd, and Dy) ordered antiferromagnetically at low temperatures.
For Ce2NiGe3 compound, the magnetic resistivity show as -lnT dependence from room temperature to 80 K and other portion of a very faint -lnT dependence from 20 K to 6 K. The magnetic resistivity increases as the temperature is lowered, instead of steadily decreasing, and decreases with the decrease of the temperature below 6 K, this magnetic contribution to the resistivity is similar to that of a Kondo lattice system.

口試委員會審定書.. i
誌謝..... ii
中文摘要. iii
Abstract.iv
Table of contents. v
List of Figures... vii
List of Tables.... x

Chapter 1 Introduction..... 1

Chapter 2 Experimental Detail....... 3

a. Sample Preparation...... 3
b. X-ray diffraction....... 4
c. Electrical Resistivity Measurement........ 5
d. Magnetization and magnetic susceptibility measurement....... 6
e. 3He refrigerator........ 7

Chapter 3 Theoretical Model 12

a. The electrical resistivity of metals and compounds. 12
b. Magnetic orderings in the low temperature. 14

Chapter 4 Crystallographic structure, magnetic, and electrical resistivity studies on R2NiGe3.... 16

a. Y2NiGe3........ 16
b. La2NiGe3....... 18
c. Ce2NiGe3....... 20
d. Pr2NiGe3....... 26
e. Nd2NiGe3....... 30
f. Sm2NiGe3....... 34
g. Gd2NiGe3....... 39
h. Dy2NiGe3....... 43
i. Ho2NiGe3....... 46

Chapter 5 Discussion....... 50

a. Crystallographic structures...... 50
b. Electrical resistivity and Magnetic orderings...... 54

References........ 56

1.Subham Majumdar and E.V. Sampathathkumaran,“Observation of enhanced magnetic transition temperature in Nd2PdGe3 and superconductivity in Y2PdGe3”. Phys. Rev. B 63, (2001) 3360.
2.E.V. Sampathathkumaran, Subham Majumdar, W. Schneider, S.L. Molodtsov, C. Laubschat,“Superconductivity in Y2PdGe3”,Physica B 312-313, (2002) 61-64.
3.Subham Majumdar, M. Mahesh Kumar, E.V. Sampathathkumaran,“Magnetic behavior of a new compound, Gd2PdGe3”J. of Alloys and comp., 61-64, (1999) 288.
4.G. T. Meaden, Electrical Resistance of Metals, Plenum Press,1965
5.Theodore Van Duzer, Charles W. Turner, Principles of Superconductive Devices and Circuits, Prentice Hall PTP, 1999, 2nd Ed.
6.U. Mizutani, Introduction to the Electron Theory of Metals, Cambridge University Press, 2001.
7.Allan H. Morrish, The Physical Principles of Magnetism, John Wiley & Sons, 1965.
8.N. W. Ashcroft, N. D. Mermin, Solid State Physics, Saunders College Publishing, 1976.
9.P. Svoboda. M. Divis, E. Gratz, R. Cerny, and L. Dobiasova, "Susceptibility and magnetization of SmCu5", Phys. Stat. Sol. A 123, K149 (1991).
10.A. M. Stewart, Phys. Rev. B 6, (1972) 1985
11.D. Mazzone, P. Riani, M. Napoletano, and F. Canepa,“The magnetism of Sm3Ag4Sn4 and Gd3Ag4Sn4”, J.Alloys Comp.387,15 (2005).
12.Structure determination of the new rare-earth compound Ce2PdGe3”, South African Journal of Science 99 (2003)
13.Z Hossain, L C Gupta and C Geibel,“Magnetic transition in the Kondo lattice system CeRhSn2”, J. Phys.：Condens. Matter 14 (2002) 9687- 9691
14.Yoshichika Onuki, Yoshiaki Shimizu, Munekazu Nishihara, Yohichi Machii, and Takemi Komatsubara“Kondo Lattice Formation in CexLa1-xCu6”J. Phys. Soc. Jpn.54,1964-1974(1985)
15.Dexuan Huo, Junji Sakurai, Tomohiko Kuwai, and Yosikazu Isikawa,“Electric, magnetic, and thermal properties of Ce2NiGe3：A Kondo lattice compound showing spin glass behavior”, Phys. Rev. B 64, (2001) 224405
16.Z. Hossain, S. Hamashima, K. Umeo, T. Takabatake, C. Geibel, and F. Steglich“Antiferromagnetic transitions in the Kondo lattice system Ce2Ni3Ge5”, Phys. Rev. B 62, (2000) 8905
17.C. Kittel“Introduction to Solid State Physics, 6th ed.”(New York:Wiley,1986)