本論文以電子束微影及直流磁控濺鍍方式製作附有菱形、正方形、圓盤形、環形與針形等五種reservoir的樣品，線寬變化的半圓環形樣品，及具膜厚變化的自旋閥樣品，和深度改變的溝渠次微米鎳鐵線，然後利用這些不同形狀、線寬、深度的圖案化磁性樣品，搭配巨磁阻自旋閥或鎳鐵薄膜，討論其翻轉磁場、電流與磁區結構之間的關係，並藉由磁場的改變或由極化電流的注入，來觀察樣品電性與磁性的變化，並且搭配數值模擬軟體(OOMMF)，了解樣品的磁區結構在外加磁場中的翻轉行為。
由不同reservoir在其連接處會產生不同的夾角角度，我們觀察到翻轉場(switching field)隨著reservoir與連接處角度增加而降低，此實驗數據與模擬結果一致，由上述樣品的研究，我們發現樣品的磁區壁(domain wall, DW)形態均為渦旋態(vortex DW)。在深度變化的溝渠次微米鎳鐵線中，溝渠深度會影響翻轉場的大小，利用磁力顯微鏡的即時場掃描與電性量測結果作比較，在電性與磁力顯微鏡相位分析結果裡，隨著溝渠深度的增加，其翻轉場大小也隨著增加。在不同線寬的半圓環形樣品中，因線寬不同在轉折處不連續區容易有磁區或磁區壁的產生，磁區壁在轉折處會有不同的釘扎力(pinning force)，即是翻轉場的不同；又半圓環翻轉場隨其線寬增加而降低，在電流驅動下，翻轉鎳鐵層(Py)與鈷層(Co)的電流密度分別為3×107 A/cm2與2×108 A/cm2。在變化膜層厚度的自旋閥樣品實驗中，我們固定磁性自由層厚度，改變磁性固定層的厚度，觀察自旋極化與厚度的影響，藉由磁場的改變或是由極化電流的注入，來研究樣品磁性與電性的關係，隨著磁性固定層厚度的增加，磁阻變化(MR ratio)最大值出現於厚度21nm處，而其臨界翻轉電流(Ic)呈現一個最小值，由分析結果得到了最大效率(磁阻)與最小耗損(臨界電流)的關係，並發現磁阻變化率與臨界電流密度(Jc)的乘積接近4.5±0.5×107 A/cm2。

Magnetic patterns with different shape and structure were fabricated by e-beam lithography and lift-off techniques to investigate their special properties. It includes four parts of experiments: 1. Switching field and the contact angle dependence in giant magnetoresistance (GMR) spin-valve wires with five different shaped reservoirs. 2. The depth of the trench and switching field dependence in the permalloy (Py) wires. 3. Numbers of steady-states in half-ring chains spin-valve with various linewidth. 4. The thickness dependence of hard layer in the pseudo spin-valve elements.
For the spin-valve wires with different shaped reservoirs, the contact angle of the wires and reservoirs provides different injection of magnetic domain wall. The switching field increases with the decreasing of contact angle. The magnetization reversal processes obtained experimentally were consistent and illustrated by using the micromagnetic simulation program, OOMMF.
The dependence between the depth of trench and the switching field in Py wires was observed by using a real-time magnetic force microscopy (MFM) and electrical measurement. The coercive and switching fields were increased with increasing the depth of trenches. The MFM images also clearly illustrated the magnetization reversal and magnetic domain structure in the different trench samples.
In the half-ring chains spin-valves with different linewidth, domain walls are significantly created at the corners between the two half rings. In the MR measurements, the domain walls at the different linewidth corners provide the difference of the switching field due to different pinning force. Numbers of steady states were obtained and attributed to the different switching fields. The experiment of current induce magnetization reversal was also observed in the samples. The critical current densities at zero magnetic field were 3×107 A/cm2 on Py and 2×108A/cm2 on Co samples, respectively.
Furthermore, in the current perpendicular to plane (CPP) GMR spin valves, the thickness of the soft layer was fixed and the hard layer was varied. The MR ratio versus the thickness of hard layer shows nonmonotonic dependence. The maximum valve of MR ratio was acquired when the thickness of hard layer was around 21 nm. From the current induce magnetization reversal study, the lowest critical current was acquired around the same thickness, 21 nm, of the hard layer, which was close to the spin diffusion length. Finally, we obtained experimentally the result of maximum efficiency (MR ratio) and minimum consumption (critical current) in a spintronic device. The product of MR ratio and critical current density is a constant, ~ 4.5±0.5×107 A/cm2.

中文摘要 I
Abstract II
誌謝 IV
Contents V
List of Figures VII
List of Tables XIII

Chapter 1 Introduction 1
Chapter 2 Basis of Magnetoresistance, Domain and Current-driven Research 5
2.1 Introduction of the Magnetoresistance 5
2.1.1 Giant magnetoresistance(GMR) 6
2.1.2 Colossal magnetoresistance (CMR) 10
2.1.3 Tunneling magnetoresistance (TMR) 13
2.1.4 Anisotropic magnetoresistance (AMR) 16
2.2 Magnetic domain walls and domains 19
2.2.1 Magnetostatic energy 20
2.2.2 Magnetocrystalline energy 21
2.2.3 Magnetostrictive energy 22
2.2.4 Domain walls 22
2.3 Magnetoresistance and Current-Driven Research of Various Patterns 26
2.3.1 Domain wall injection into ferromagnetic submicron wires 26
2.3.2 The current-induced propagation of magnetic domain walls 28
2.3.3 The injection current affects the localized magnetic moment 30
2.3.4 The domain wall trapping and motion at some geometrical confinement 33
2.3.5 The effect of modifying the layer thickness of a current–perpendicular -to-plane spin valve structure 35
Chapter 3 Experimental facilities and measurement methods 39
3.1 Scanning electron microscope (SEM) 39
3.2 Deposition system 40
3.3 Optical lithography 42
3.4 Electron beam lithography system 43
3.5 The measurement of magnetoresistance 45
3.6 Atomic force microscopy and magnetic force microscopy 48
3.7 The injection of the pulse current 50
3.8 Simulation software used in the experiment 51
Chapter 4 Results and Discussion 53
4.1 Domain wall injection in spin valve systems with reservoirs of different geometry 53
4.1.1 Fabrication of these reservoirs of different geometry 53
4.1.2 The results of magnetoresistance (MR) measurement 54
4.1.3 The results of micromagnet simulation software OOMMF 59
4.1.4 The results of magnetic force microscope measurement 66
4.2 Magnetization reversal and domain wall pinning in submicron permalloy wires with different depth trenches 69
4.2.1 Fabrication of the wire with different trenches 69
4.2.2 The results of magnetic force microscope measurement 70
4.2.3 The results of magnetoresistance (MR) measurement 73
4.3 Current-driven domain wall in giant magnetoresistance half-ring series wires with varied linewidth 76
4.3.1 Fabrication of half-ring wires 76
4.3.2 The results of magnetoresistance (MR) measurement 77
4.3.3 The results of current-driven measurement 79
4.4 Compensation between magnetoresistance and switching current in Co/Cu/Co spin valve pillar structure 84
4.4.1 Fabrication of the CPP pillar structure 84
4.4.2 The results of magnetoresistance (MR) measurement 85
4.4.3 The results of current-driven measurement of CPP spin valve 87
Chapter 5 Conclusions 96
References 98
Publications 106

[1] M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen van Dau, F. Petroff, P. Eitenne, G. Creuzet, A. Friederich and J. Chazelas, “Giant Megnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices”, Phys. Rev. Lett., vol. 61, p.2472, 1988.
[2] D. A. Allwood, Gang Xiong, M .D. Cooke, C. C. Faulkner, D.Atkinson, N. Vernier, and R. P. Cowburn, “Submicrometer Ferromagnetic NOT Gate and Shift Register”, Science, vol. 296, p.2003, 2002.
[3] Gary A. Prinz, “Magnetoelectronics”, Science, vol. 282, p.1660, 1998.
[4] S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. von Molnar, M. L. Roukes, A. Y. Chtchelkanova, and D. M. Treger, “Spintronics: A Spin-Based Electronics Vision for the Future”, Science, vol. 294, p.1488, 2001.
[5] R. P. Cowburn, D. A. Allwood, G. Xiong, and M .D. Cooke, “Domain wall injection and propagation in planar Permalloy nanowires”, J. Appl. Phys., vol. 91, p.6949, 2002.
[6] J. C. Slonczewski, “Current-driven excitation of magnetic multilayers”, J. Magn. Magn. Mater., vol. 159, p.L1, 1996.
[7] M. Tsoi, A. G. M. Jansen, J. Bass, W.–C. Chiang, M. Seck, V. Tsoi, and P. Wyder, “Excitation of a Magnetic Multilayer by an Electric Current”, Phys. Rev. Lett., vol. 80, p.4281, 1998.
[8] S. Urazhdin, Norman O. Birge, W. P. Pratt, Jr., and J. Bass, Phys. Rev. Lett., “Current-Driven Magnetic Excitations in Permalloy-Based Multilayer Nanopillars” vol. 91, p.146803, 2003.
[9] J. Grollier, V. Cros, A. Hamzic, J. M. George, H. Jaffres, A. Fert, G. Faini, J. Ben Youssef, and H. Legall, “Spin-polarized current induced switching in Co/Cu/Co pillars”, Appl. Phys. Lett., vol. 78, p.3663, 2001.
[10] Robert C. O. Handley, “Modern Magnetic Materials–Principles and Applications”, Wiley-Interscience, 1999.
[11] N. A. Spaldin, “Magnetic Materials-Fundamentals and Device Applications”, Cambridge university press, 2003.
[12] P. Grunberg, R. Schreiber, Y. Pang, M. B. Brodsky, and H. Sowers, “Layered Magnetic Structures: Evidence for Antiferromagnetic Coupling of Fe Layers across Cr Interlayers”, Phys. Rev. Lett., vol. 57, p.2442, 1986.
[13] C. Carbone and S. F. Alvarado, “Antiparallel coupling between Fe layers separated by a Cr interlayer: Dependence of the magnetization on the film thickness”, Phys. Rev. B, vol. 36, p.2433, 1987.
[14] G. Binasch, P. Grunberg, F. Saurenbach, and W. Zinn, “Enhanced magnetoresistance in layered magnetic structures with antiferromagnetic interlayer exchange”, Phys. Rev. B, vol. 39, p.4828, 1989.
[15] John Q. Xiao, J. Samuel Jiang, and C. L. Chien, “Giant Magnetoresistance in Nonmultilayer Magnetic Systems”, Phys. Rev. Lett., vol. 68, p.3749, 1992.
[16] G. H. Jonker and J. H. van Santen, “Ferromagnetic compounds of manganese with perovskite structure”, Physica, vol. 16, p. 377, 1950.
[17] R. von Helmolt, J. Wecker, B. Holzapfel, L. Schultz, and K. Samwer, “Giant negative magnetoresistance in perovskitelike La2/3Ba1/3MnOx ferromagnetic films”, Phys. Rev. Lett., vol. 71, p.2331, 1993.
[18] S. Jin, T. H. Tiefel, M. McCormack, R. A. Fastnacht, R. Ramesh, and L. H. Chen, “Thousandfold Change in Resistivity in Magnetoresistive La-Ca-Mn-O Films”, Science, vol. 264, p.413, 1994.
[19] G. Xiao, A. Gupta, X. W. Li, G. Q. Gong, and J. Z. Sun, “Sub-200 Oe Giant Magnetoresistance in Manganite Tunnel Junctions”, Mater. Res. Soc. Symp. Proc., vol. 494, p.221, 1998.
[20] J. B. Goodenough, “Theory of the Role of Covalence in the Perovskite-Type Manganites [La, M(II)]MnO3”, Phys. Rev., vol. 100, p.564, 1955.
[21] E. O. Wollan and W. C, Koehler, “Neutron Diffraction Study of the Magnetic Properties of the Series of Perovskite-Type Compounds [(1-x)La, xCa]MnO3”, Phys. Rev., vol. 100, p.545, 1955.
[22] P. Schiffer, A. P. Ramirez, W. Bao, and S.–W. Cheong, “Low Temperature Magnetoresistance and Magnetic Phase Diagram of La1-xCaxMnO3”, Phys. Rev. Lett., vol. 75, p.3336, 1995.
[23] C. Zener, “Interaction between the d-Shells in Transition Metals. II. Ferromagnetic Compounds of Manganese with Perovskite Structure”, Phys. Rev., vol. 82, p.403, 1951.
[24] M. Julliere, “Tunneling between ferromagnetic films”, Phys. Lett. A, vol. 54, p.225, 1975.
[25] S. Yuasa, T. Nagahama, A. Fukushima, Y. Suzuki, and K. Ando, “Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions”, Nat. Mat., vol. 3, p.868, 2004.
[26] S. S. P. Parkin, C. Kaiser, A. Panchula, P. M. Rice, B. Hughes, M. Samant, and S. H. Yang, “Giant tunneling magnetoresistance at room temperature with MgO (100) tunnel barriers”, Nat. Mat., vol. 3, p.862, 2004.
[27] J. Kondo, “Anomalous Hall Effect and Magnetoresistance of Ferromagnetic Metals”, Prog. Theor. Phys., vol. 27, p.772, 1962.
[28] Robert C. O’handley, “Modern Magnetic Materials: Principles and Applications”, John Wiley & Sons Inc., 1999.
[29] F. Block, “Zur Theorie des Austauschproblems und der Reman-enzerscheinung der Ferromagnetika”, Z. Phys, vol. 74, p.295, 1932.
[30] L. Landau and E. Lifshitz, “On the theory of magnetic permeability in ferromagnetic bodies”, Phys. Z. Sowjetunion, vol. 8, p.153, 1935.
[31] M. Ziese and M. J. Thornton, “Spin Electronics”, Springer, Heidelberg, 2001.
[32] R. Skomski and J. M. D. Coey, “Permanent Magnetism”, (Institute of Physics, Bristol, 1999).
[33] S. Chikazumi, “Physics of Magnetism”, John Wiley & Sons Inc., 1964.
[34] D. A. Allwood, G. Xiong, C.C. Faulkner, D. Atkinson, D. Petit, R. P. Cowburn, “Magnetic Domain-Wall Logic”, Science, vol. 309, p.1688, 2005.
[35] L. Berger, “Low-field magnetoresistance and domain drag in ferromagnets”, J. Appl. Phys., vol. 49, p.2156, 1978.
[36] L. Berger, “Motion of a magnetic domain wall traversed by fast-rising current pulses”, J. Appl. Phys., vol. 71, p.2721, 1992.
[37] W. Y. Lee, C. C. Yao, A. Hirohata, Y. B. Xu, H. T. Leung, S. M. Gardiner, S. McPhail, B. C. Choi, D. G. Hasko, and J. A. C. Bland, “Domain nucleation processes in mesoscopic Ni80Fe20 wire junctions”, J. Appl. Phys., vol. 87, p.3032, 2000.
[38] J. Wunderlich, D. Ravelosona, C. Chappert, F. Cayssol, V. Mathet, J. Ferre, J. –P. Jamet, and A. Thiaville, “Influence of geometry on domain wall propagation in a mesoscopic wire”, IEEE Trans. Magn., vol. 37, p.2104, 2001.
[39] K. Shigeto, T. Shinjo, and T. Ono, “Injection of a magnetic domain wall into a submicron magnetic wire”, Appl. Phys. Lett., vol. 75, p.2815, 1999.
[40] L. Thomas, C. Rettner, M. Hayashi, M. G. Samant, S. S. P. Parkin, A. Doran, and A. Scholl, “Observation of injection and pinning of domain walls in magnetic nanowires using photoemission electron microscopy”, Appl. Phys. Lett., vol. 87, p.262501, 2005.
[41] D. McGrouther, S. McVitie, J. N. Chapman, and A. Gentils, “Controlled domain wall injection into ferromagnetic nanowires from an optimized pad geometry”, Appl. Phys. Lett., vol. 91, p.022506, 2007.
[42] M. Tsoi, R. E. Fontana, and S. S. P. Parkin, “Magnetic domain wall motion triggered by an electric current”, Appl. Phys. Lett., vol. 83, p.2617, 2003.
[43] W. J. Carr, “Propagation of magnetic domain wall by a self-induced current distribution”, J. Appl. Phys., vol. 45, p.394, 1974.
[44] L. Berger, “Prediction of a domain-drag effect in uniaxial, non-compensated, ferromagnetic metals”, J. Phys. Chem. Solids, vol. 35, p.947, 1974.
[45] T. Kimura, Y. Otani, K. Tsukagoshi, and Y. Aoyagi, “Spin-current-assisted domain-wall depinning in a submicron magnetic wire”, J. Appl. Phys., vol. 94, p.7947, 2003.
[46] D. Lacour, J. A. Katine, L. Folks, T. Block, J. R. Childress, M. J. Carey, and B. A. Gurney, “Experimental evidence of multiple stable locations for a domain wall trapped by a submicron notch”, Appl. Phys. Lett., vol. 84, p.1910, 2004.
[47] A. J. Zambano, and W. P. Pratt, Jr., “Detecting domain-wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant megnetoresistance”, Appl. Phys. Lett., vol. 85, p.1562, 2004.
[48] L. Berger, ”Emission of spin waves by a magnetic multilayer traversed by a current”, Phys. Rev. B, vol. 54, p.9353, 1996.
[49] S. G. Tan, M. B. A. Jalil, S. Bala Kumar, G. C. Han, and Y. K. Zheng, “Layer thickness effect on the magnetoresistance of a current-perpendicular-to-plane spin valve”, J. Appl. Phys., vol. 100, p.063703, 2006.
[50] M. Tsoi, J. Z. Sun, and S. S. P. Parkin, “Current-Driven Excitations in Symmetric Magnetic Nanopillars”, Phys. Rev. Lett., vol. 93, p.036602, 2004.
[51] E. B. Myers, D. C. Ralph, J. A. Katine, R. N. Louie, R. A. Buhrman, “Current-Induced Switching of Domains in Magnetic Multilayer Devices”, Science, vol. 285, p. 867, 1999.
[52] F. J. Albert, N. C. Emley, E. B. Myers, D. C. Ralph, and R. A. Buhrman, “Quantitative Study of Magnetization Reversal by Spin-Polarized Current in Magnetic Multilayer Nanopillars”, Phys. Rev. Lett., vol. 89, p.226802, 2002.
[53] L. Berger, “Spin-wave emitting diodes and spin diffusion in magnetic multilayer”, IEEE Trans. Magn., vol. 34, p.3837, 1998.
[54] C. Heide, “Spin Currents in Magnetic Films”, Phys. Rev. Lett., vol. 87, p.197201, 2001.
[55] P. C. van Son, H. van Kempen, and P. Wyder, “Boundary Resistance of the Ferromagnetic-Nonferromagnetic Metal Interface”, Phys. Rev. Lett., vol. 58, p.2271, 1987.
[56] N. F. Mott, “The Electrical Conductivity of Transition Metals”, Proc. R. Soc. London, vol. 153, p.699, 1936.
[57] A. Fert and I. A. Campbell, “Two-Current Conduction in Nickel”, Phys. Rev. Lett., vol. 21, p.1190, 1968.
[58] W. P. Pratt, Jr., S. -F. Lee, J. M. Slaughter, R. Loloee, P. A. Schroeder, and J. Bass, “Perpendicular giant magnetoresistance of Ag/Co multilayers”, Phys. Rev. Lett., vol. 66, p.3060, 1991.
[59] M. Johnson and R. H. Silsbee, “Thermodynamic analysis of interfacial transport and of the thermomagnetoelectric system”, Phys. Rev. B, vol. 35, p.4959, 1987.
[60] M. J. Donahue and D. G. Porter, OOMMF User’s Guide, NIST object oriented magnetic modeling framework (http://math.nist.gov/oommf).
[61] W. F. Brown, Jr., “Micromagnetics”, Krieger, New York, 1978.
[62] D. Buntinx, A. Volodin, and C. V. Haesendonck, “Influence of local anisotropic magnetoresistance on the total magnetoresistance of mesoscopic NiFe rings”, Phys. Rev. B, vol. 70, p.224405, 2004.
[63] B. W. Corb, “Effects of magnetic history on the domain structure of small NiFe shapes”, J. Appl. Phys., vol. 63, p.2941, 1988.
[64] S. Lepadatu and Y. B. Xu, “Direct Observation of Domain Wall Scattering in Patterned Ni80Fe20 and Ni Nanowires by Current-Voltage Measurements”, Phys. Rev. Lett., vol. 92, p.127201, 2004.
[65] S. Laribi, V. Cros, M. Munoz, J. Grollier, A. Hamzic, C. Deranlot, A. Fert, E. Martinez, L. Lopez-Diaz, L. Vila, G. Faini, S. Zoll, and R. Fournel, “Reversible and irreversible current induced domain wall motion in CoFeB based spin valves stripes”, Appl. Phys. Lett., vol. 90, p.232505, 2007.
[66] Y. C. Chen, Y. D. Yao, S. F. Lee, Y. Liou, J. L. Tsai, and Y. A. Lin, “Quantitative analysis of magnetization reversal in submicron S-patterned structures with narrow constrictions by magnetic force microscopy”, Appl. Phys. Lett., vol. 86, p.053111, 2005.
[67] J. Banhart, H. Ebert, and A. Vernes, “Applicability of the two-current model for systems with strongly spin-dependent disorder”, Phys. Rev. B, vol. 56, p.10165, 1997.
[68] J. Bass and W. P. Pratt, Jr., “Spin-diffusion lengths in metals and alloys, and spin-flipping at metal/metal interfaces: an experimentalist’s critical review”, J. Phys.: Condens. Matter, vol. 19, p.183201, 2007.
[69] R. J. Elliott, “Theory of the Effect of Spin-Orbit on Magnetic Resonance in Some Semiconductors”, Phys. Rev., vol. 96, p.266, 1954.
[70] Y. Yafet, “Spin-Orbit Induced Spin-Filp Scattering by a Local Moment”, J. Appl. Phys., vol. 42, p.1564, 1971.
[71] J. Z. Sun, “Current-driven magnetic switching in manganite trilayer junctions”, J. Magn. Magn. Mater., vol. 202, p.157, 1999.
[72] J. A. Katine, F. J. Albert, R. A. Buhrman, E. B. Myers, and D. C. Ralph, “Current-Driven Magnetization Reversal and Spin-Wave Excitations in Co/Cu/Co Pillars”, Phys. Rev. Lett., vol. 84, p.3149, 2000.
[73] F. J. Albert, J. A. Katine, R. A. Buhrman, and D. C. Ralph, “Spin-polarized current switching of a Co thin film nanomagnet”, Appl. Phys. Lett., vol. 77, p.3809, 2000.
[74] A. Fert and S. F. Lee, “Theory of the bipolar spin switch”, Phys. Rev. B, vol. 53, p.6554, 1996.
[75] E. B. Myers, F. J. Albert, J. C. Sankey, E. Bonet, R. A. Buhrman, and D. C. Ralph, “Thermally Activated Magnetic Reversal Induced by a Spin-Polarized Current”, Phys. Rev. Lett., vol. 89, p.196801, 2002.
[76] A. Barthelemy, and A. Fert, “Theory of the magnetoresistance in magnetic multilayers: Analytical expressions from a semiclassical approach”, Phys. Rev. B, vol. 43, p.13124, 1991.