Magnetization reversal of co or pd bit patterned media

MAGNETIZATION REVERSAL OF Co/Pd BIT PATTERNED MEDIA LI WEIMIN (B. ENG., HUBEI UNIVERSITY OF TECHNOLOGY, CHINA) (M. ENG., HUBEI UNIVERSITY OF TECHNOLOGY, CHINA) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING 2013 DECLARATION I hereby declare that this thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any University previously. _______________________ LI WEIMIN 03 October 2013 i ACKNOWLEDGEMENTS My deepest gratitude goes first and foremost to my supervisor, Prof. Ding Jun, for his guidance and encouragement throughout my PhD study. His patience, enthusiasm, creative ideas and immense knowledge helped me in all the time of research work and writing of this thesis. I would like to express my heartfelt gratitude to Dr. Shi Jianzhong and Dr. Xue Junmin, who are my co-supervisors for their guidance and supervision as well as insight information about the project. I am also greatly indebted to all my colleagues at Data Storage Institute (DSI) for their help and friendship, especially to Dr. Wong Seng Kai, Ms. Sim Cheow Hin and Ms. Sherry Yap Lee Koon for their technical support on sample preparation and EBL patterning, also to Dr. Huang Tianli, Mr. Lim Wee Kiat, Ms. Hnin Yu Yu Ko, Ms. Sze Jia Yin and Mr. Kelvin Cher Kiat Min for providing experimental resource and equipment training. In particular, I am grateful to Dr. Chen Yunjie for enlightening me the first glance of my research work in Singapore. Moreover, I consider it an honor to work with all former and current research members in Department of Material Science and Engineering. Special thanks should be given to Ms. Huang Lisen for her constructive advices and enthusiastic assistance in keeping my progress, to Mr. Yang Yong for guidance of LLG micromagnetic simulation, to Henry for paper revision and discussion, and Mr. Yang Zhengchun for TEM measurement. I sincerely thank National University of Singapore (NUS) for providing the 4-year research scholarship during my PhD study and DSI for providing the research ii scholar attachment. Last but not least would go to my beloved family for their loving considerations and great confidence in me all through these years. I also gratefully acknowledge the help of my friends and my fellow classmates who gave me valuable advice on my thesis. iii TABLE OF CONTENTS DECLARATION . I ACKNOWLEDGEMENTS II LIST OF PUBLICATIONS . ERROR! BOOKMARK NOT DEFINED. TABLE OF CONTENTS . IV SUMMARY X LIST OF TABLES . XIII LIST OF FIGURES .XIV LIST OF ILLUSTRATION XXIII LIST OF SYMBOLS . XXIV 1. INTRODUCTION . 1.1 A brief background of magnetic recording . 1.2 Transition from longitudinal recording to perpendicular recording 1.3 Description of various layers and their functions of PRM 1.4 Critical issues in magnetic recording media . 1.4.1 Thermal stability 1.4.2 Superparamagnetic limit 1.4.3 SNR issue . 1.4.4 The "trilemma" of magnetic recording . 10 1.5 Motivations and Objectives 11 1.6 Thesis Outline . 14 2. LITERATURE REVIEW . 18 iv 2.1 Magnetic domain structures 18 2.1.1 Magnetic domains 18 2.1.2 Magnetic domain walls in thin film . 20 2.1.3 Application of domain structures . 21 2.2 Bit patterned media for Tbit/in2 densities . 26 2.2.1 Bit Patterned media 26 2.2.2 Demagnetization field 27 2.2.3 Dipole-dipole interaction . 29 2.2.4 Switching field distribution 30 3. EXPERIMENTAL TECHNIQUES . 36 3.1 Sample preparation . 36 3.1.1 Sputtering . 36 3.1.2 Electron beam Lithography and Lift-off 37 3.2 Structure Characterization 38 3.2.1 X-ray Diffractometer (XRD) 38 3.2.2 Atomic Force Microscope (AFM) 39 3.2.3 Scanning Electron Microscope (SEM) 41 3.2.4 Transmission Electron Microscopy (TEM) 42 3.3 Magnetic Properties Characterization . 42 3.3.1 Vibrating Sample Magnetometer (VSM) . 42 3.3.2 Polar Magneto-optic Kerr Effect (MOKE) Magnetometer 44 3.3.3 Alternating Gradient Force Magnetometer (AGFM) . 46 v 3.3.4 Superconducting Quantum Interference Device (SQUID) 47 3.3.5 Magnetic Force Microscope(MFM) . 49 3.4 LLG Micromagnetics SimulatorTM . 50 4. CALCULATION OF MAGNETIZATION REVERSAL OF CO/PD BIT PATTERNED MEDIA . 52 4.1 Introduction . 52 4.2 Experimental Details . 52 4.3 Results and discussions . 53 4.3.1 Microstructures of continuous Co/Pd multilayer . 53 4.3.2 Measurement of SFD of Co/Pd islands based on MFM observation . 55 4.3.3 Calculation of switching field distribution of Co/Pd islands . 56 4.4 Conclusions . 59 5. MICROMAGNETIC SIMULATION OF MAGNETIZATION REVERSAL OF CO/PD BIT PATTERNED MEDIA 61 5.1 Introduction . 61 5.2 Methods 61 5.2.1 Experimental 61 5.2.2 Micromagnetic simulation . 63 5.3 Results and discussion 63 5.3.1 Experimental results of continuous film and MFM study on BPM . 63 5.3.2 Range of single domain island sizes for Co/Pd multilayers based BPM . 65 5.3.3 Magnetic properties of a single island . 67 vi 5.3.4 Dipole-dipole interactions 69 5.3.5 Switching Field (SF) and SFD for Bit patterned area 72 5.4 Conclusions . 75 6. ANGULAR DEPENDENCE AND TEMPERATURE EFFECT ON MAGNETIZATION REVERSAL OF CO/PD BIT PATTERNED MEDIA 77 6.1 Introduction . 77 6.2 Experimental details 77 6.3 Results and discussions . 78 6.3.1 Temperature dependence of SFD of Co/Pd islands 78 6.3.2 Angular dependence of SFD of Co/Pd islands . 83 6.4 Conclusions . 86 7. MAGNETIC ISLANDS WITH CONFIGURABLE DOMAIN STRUCTURES VIA DIPOLE-DIPOLE INTERACTIONS AND THEIR POSSIBLE APPLICATIONS 87 7.1 Introduction . 87 7.2 Experimental . 89 7.3 Results and discussion 89 7.3.1 Configurable magnetic islands cluster via dipole-dipole interaction . 89 7.3.2 Demonstration of the [Co/Pd] multi-islands cluster . 93 7.4 Application of configurable magnetic islands via dipole-dipole interaction . 106 7.4.1 Multi-states bit patterned media . 106 7.4.2 Configurable associative memory 108 vii 7.5 Conclusions . 113 8. THE EFFECT OF CAPPED LAYER THICKNESS ON SWITCHING BEHAVIOR IN PERPENDICULAR COCRPT BASED COUPLED GRANULAR/CONTINUOUS MEDIA 115 8.1 Introduction . 115 8.2 Experiments 117 8.3 Results and discussion 119 8.3.1 microstructures of the CGC media . 119 8.3.2 Macroscopic magnetic properties 121 8.3.3 Intrinsic magnetic properties 123 8.3.4 Micromagnetic simulation . 126 8.4 Conclusion 130 9. CONCLUSIONS AND FUTURE WORK 132 9.1 Conclusions from this work 132 9.1.1 Continuous [Co3/Pd8]10 multilayer . 132 9.1.2 Patterned Co/Pd islands . 133 9.1.3 Calculation of SFD in Co/Pd based bit patterned media 133 9.1.4 Micromagnetic simulation of SFD in Co/Pd based bit patterned media 134 9.1.5 Temperature and angular dependence of SFD in Co/Pd BPM 135 9.1.6 Configurable domain structures via dipole-dipole interactions . 135 9.1.7 Switching behavior in CoCrPt based coupled media . 136 9.2 Possible improvements for future work 137 viii 9.2.1 multi-states bit patterned media . 137 9.2.2 Configurable associative memory 139 10. BIBLIOGRAPHY . 141 11. APPENDIX 147 11.1 List of publications 147 ix CHAPTER CONCLUSIONS AND FUTURE WORK 9. Conclusions and Future Work 9.1 Conclusions from this work The development of bit patterned media (BPM) has become one of the necessary requirements to meet the ever-growing demand for ultra-high recording densities of up to 50Tbit/in2 by theoretical predictions. One of the critical issues for BPM in ultra-high recoding density is that the SFD (defined as a dispersion of switching fields for magnetic islands in BPM) needs to be narrow enough to secure exact addressability of individual predefined bits without overwriting adjacent bits. This work is rooted in understanding of the magnetic physics in bit patterned media, including the specifics of magnetization reversal, the source of SFD, and the contribution of dipole-dipole interactions on broadening of SFD in BPM arrays. Based on the detailed investigation, the conclusions in this work and possible improvements in the future work are summarized below: 9.1.1 Continuous [Co3/Pd8]10 multilayer [Co3/Pd8]10 multilayer with large out-of-plane anisotropy is fabricated by dc magnetron sputtering on a thermally oxidized Si substrate. The number following the symbols is the respective layer thickness in angstrom and the subscript refers to the number of repetitions. The films are deposited on [Ta50/Cu50/Pd30] to induce proper crystallographic growth of the Co layer and capped with [Pd30/Ta50] for protection. The in-plane and out-of-plane hysteresis loops of the continuous Co/Pd multilayer shows a large perpendicular anisotropy with a magnetic anisotropy field of 34 kOe, saturation magnetization of 470 emu/cc, and an out-of-plane coercivity Hc of 780 Oe, 132 CHAPTER CONCLUSIONS AND FUTURE WORK which makes this material a promising candidate for high density data storage. A strong face-centered-cubic (fcc)-CoPd (111) peak and a weak fcc-CoPd (200) peak were observed at around 40.8°and 47.9° by XRD, respectively, showing a strong (111) texture, which is favorable for large perpendicular anisotropy and high coercivity. 9.1.2 Patterned Co/Pd islands The patterned dots are successfully generated using high resolution electron beam lithography by first coating the film with hydrogen silsesquioxane (HSQ) photoresist and followed by Ar+ ion-milling at angle of 3º off normal incidence to the sample to form discrete magnetic islands. Continuous Co/Pd multilayer is patterned to 11x11 islands with island size of 80 nm and pitch size of 100 nm. We Successful observed magnetization reversal of individual Co/Pd islands one by one through magnetic force microscope, indicating well separation and smaller dipole-dipole interaction between islands. Based on MFM observation, the magnetization of the patterned area is calculated by counting islands switched or not at different magnetic fields. Number of switched islands as a function of applied fields is plotted as switching field distribution curve. Intrinsic SFD for BPM is calculated from ∆H (M, ∆M) method by removing dipole-dipole interactions. 9.1.3 Calculation of SFD in Co/Pd based bit patterned media Calculation of SFD based on intrinsic SFD is done to verify if dipole-dipole interactions contribute to the SFD broadening. In this part, [Co/Pd] island is considered as a uniform "single spin". We used the formula in the calculation of critical switching field for the individual islands: Hc=Hc, int-ΣMs 133 ×V bit/r , where Hc is CHAPTER CONCLUSIONS AND FUTURE WORK the critical field, Hc,int is the initial critical field without dipole-dipole interactions, and Σ represents the dipole-dipole interactions form neighbored islands. Hc,int was generated from the obtained initial SFD (2σ=1.2 kOe). Dipole-dipole interactions cause a significant SFD broadening (2σ=2.0 kOe). The width of 2σ= 1.7 kOe after the calculation with the consideration of the dipole-dipole distribution is in a relatively good agreement with our experimental data (2σ=2.0 kOe). The calculated demagnetization loop also agrees well with our experimental result. 9.1.4 Micromagnetic simulation of SFD in Co/Pd based bit patterned media In calculation, we assumed each [Co/Pd] island is uniform and can be considered as "a single spin". However, based on calculation of exchange length (~ 8.5 nm, which is much smaller than island size of 80nm), the island can’t be considered as a single spin. In this part, non-uniform magnetization configurations in patterned area is considered by LLG simulation. The range of single domain island size based on Co/Pd island with thickness of 12 nm was determined by micromagnetic simulation based on Landau-Lifshitz-Gilbert equation. Demagnetization effect, dipole-dipole interactions and switching field distribution (SFD) for Co/Pd based bit patterned media were also quantitatively studied by simulation. The simulated total hysteresis loops and SFD were comparable with the experimental ones. The SFD increased from 2σ =1.2 kOe (as the calculated intrinsic SFD) to the experimental value of 1.9 kOe due to dipole-dipole interactions which is in a good agreement with the experimental results (2.0 kOe). Therefore, islands in the patterned area were not strictly switching coherently (single spins), the process was rather a kind of nucleation followed by 134 CHAPTER CONCLUSIONS AND FUTURE WORK rapid domain wall propagation. Defects in Co/Pd multilayer patterned islands are not only simply regions of reduced anisotropy but also exhibit a more complicated behavior that includes a deviation in anisotropy axis. Optimized patterned structure with a minimized SFD and maximized data storage densities was found to have an island size of 10 nm and islands separation of 20 nm. The calculated ratio of SFD/Hc (Hc: the coercivity) is 9.2%, which is below the threshold of 10% for 1Tb/in2 pattern media. 9.1.5 Temperature and angular dependence of SFD in Co/Pd based bit patterned media Is the SFD related to other effect? Temperature effect and angle dependence of critical fields (Hcr) and switching field distribution (SFD) are studied by both experiment and simulation. From our observation, when temperature increases from 77 K to 300 K, critical field of patterned area decreases from 13kOe to 11kOe. Absolute SFD decreases from 2.6 kOe to 2.2 kOe as thermal energy assists islands reversal. The relative SFD (SFD/Hcr) keeps constant with temperature. Although critical fields and absolute SFD vary with angles, relative SFD is independent of the field angle. The interactions between islands broaden relative SFD from 12% to 20% after considering dipole-dipole interactions. The relative SFD by simulation agrees well with our experimental observation. 9.1.6 Configurable domain structures of Co/Pd islands via dipole-dipole and their possible applications. In BPM sample, dipole-dipole interaction is designed to be as weak as possible 135 CHAPTER CONCLUSIONS AND FUTURE WORK for high areal density. However, dipole-dipole interaction can not be avoid in closely arranged islands. Therefore, in this chapter, we want to make good use of dipole-dipole interaction (as strong as possible) to generate different magnetic states, which is configurable by external field. In order to investigate how dipole-dipole interaction (rather than deviation in properties of magnetic islands) makes contribution to the switching field distribution, we expect to find out a kind of magnetic film with homogenous properties after patterned into to magnetic islands. Based on pervious chapters, we find that Co/Pd islands have uniform magnetic properties. Therefore, in this chapter, we use Co/Pd islands to the experimental demonstration. Configurable domain structures of Co/Pd islands via dipole-dipole interactions are investigated by both experiment and micromagnetic simulation. A “multi-states bit for magnetic recording” consisting of closely arranged magnetic islands is successfully designed to achieve ultra-high magnetic recording density. A simple and configurable associative memory combining the inherent advantages of a non-volatile output with flexible functionality which can be selected at run-time to operate as an AND, OR, NAND or NOR gate. These schemes show a huge potential for data storage industry and magnetic associative memory design. 9.1.7 The effect of capped layer thickness on switching behavior in perpendicular CoCrPt based coupled granular/continuous media A systematic investigation of magnetic switching behavior of CoCrPt based capped media consisting of granular layer and capped layer is performed by varying the thickness of the capped layer from to 9nm. CoCrPt magnetic grains are 136 CHAPTER CONCLUSIONS AND FUTURE WORK separated by nonmagnetic oxide grain boundaries. Grain size and grain boundary are about 8.9 nm and nm, respectively. The nonmagnetic oxide grain boundaries in the granular layer not disappear immediately at the interface between the granular and capped layers. The amorphous grain boundary phase in the granular layer propagates to the top surface of the capped layer. After capping with the CoCrPt(B) layer, the grain size at the surface of CGC structure increases and the grain boundary decreases. Besides, although Hc apparently decreases at thicker capped layer, no obvious variation of macroscopic switching field distribution (SFD/Hc) is observed. We separate intrinsic switching field distribution from intergranular interactions. The investigation of reduced intrinsic SFD/Hc and increased hysteresis loop slope at coercivity, suggests that improvement of absolute switching field distribution (SFD) is caused by both strong intergranular exchange coupling and uniform grain size. Micromagnetic simulation results further verify our conclusion that the capped layer in CGC media is not uniformly continuous but has some granular nature. However, grains in the CoCrPt(B) capped layer is not absolutely isolated, strong exchange coupling exists between grains. 9.2 Possible improvements for future work Based on systematically investigation of magnetization reversal of Co/Pd bit patterned media by both exeperimental and theoretical simulation in this work, several potential directions for future research are highlighted below: 9.2.1 Multi-states bit patterned media Bit patterned media, which may provide thermal stability at very modest 137 CHAPTER CONCLUSIONS AND FUTURE WORK anisotropy values due to well lithography patterned ordered arrays. However, conventional bit patterned media still meet several serious challenges for mass product in hard disk drive industry. First of all, strong exchange coupling between closely arranged bits may lead to recording failure because the head pole (100~200nm) can no longer address exactly on individual predefined bits without overwriting adjacent bits. Secondly, track width is limited by head pole. Take 2013 hard disk drive product in Seagate Technology for example, the track width is 65nm while the bit size is about 13nm. Low bit width-to-length ratio in bit patterned media (13nm:13nm in BPM compared to 65nm:13nm in conventional granular media for 700Gbit/in2) will have severe implications for the requirements on the servo tracking system and may result in undesirably low data throughput rates. Last but not the least, with velocities of the write element relative to the media in the range 15 to 30 nm/ns, a 12 nm separation of the islands implies that the magnetic write field needs to be fully reversed in 0.8 to 1.7 ns. In itself this seems attainable, however small random variations in rotational speed of the disc, placement of the islands during disc manufacturing, and variability in magnetic properties of the patterned bits will introduce errors in the recording process, i.e. bits will be “missed”. Increasing the number of bits stored within each island in a multilevel storage is believed as an alternative approaches to increasing storage density without reducing the bit size. Storage schemes with different multi-state structures have been proposed using both in-plane and perpendicular anisotropy materials. Concept of three-dimensional (3D) magnetic memory is raised by stacking two decoupled layers with different coercivity 138 CHAPTER CONCLUSIONS AND FUTURE WORK or different magnetization (in-plane or out-of-plane). However, the realization of 3D magnetic memory meets great challenge in achieving narrow switching field distribution due to compensated demagnetizing fields of different storage layers with increasing storage density. Although a “multi-states bit for magnetic recording” consisting of closely lithography patterned islands is proposed and magnetic states are predicted by simulation results, experiments are needed to confirm this proposal. Magnetization reversal of magnetic clusters consisting of three islands with size smaller than 10nm and separation also smaller than 10nm is expected to be investigated by MFM observations at different magnetic fields. Distinct switching fields for islands inside of a cluster is the premise for the further design and application of multi-states bit patterned media. 9.2.2 Configurable Associative Memory Magnetic islands with configurable domain structures show a huge potential in application of spintronic associative memory. Nowadays, further improvements in conventional chips technology based on complementary metal-oxide-semiconductor (CMOS) are limited by several issues including power consumption, energy dissipation, down-scaling of gate dimensions, etc. Nanomagnet logic (NML) elements which are reconfigurable at run-time shows potential advantages over the rigid architecture of the present hardware systems. It processes and propagates information (logic and logic 0) through mutual interaction between neighboring nanoscale magnets, magnetic switching or domain wall motion which can be adjusted by an 139 CHAPTER CONCLUSIONS AND FUTURE WORK external magnetic field or spin-polarized current. However, electron spins or magnetizations are usually less coherent than electron charges and accurately controlling spin has been a relatively more difficult task than transporting electrons for a long time. Simple and function-flexible logic structure is expected for the future nanomagnet logic. Although associative memory combining the inherent advantages of a non-volatile output with flexible functionality which can be selected at run-time to operate as an AND, OR, NAND or NOR gate is successfully designed in this work, it just stay in the model level. Many effects should be considered in the fabrication of this associative memory, such as the thickness of the metallic layer or how to improve GMR effect of the device, etc. 140 10. BIBLIOGRAPHY 1. S. N. Piramanayagam and K. Srinivasan, Journal of Magnetism and Magnetic Materials 321 (6), 485-494 (2009). 2. S. N. Piramanayagam, Journal of Applied Physics 102 (1), 011301-011322 (2007). 3. S. Z. Wu, Magnetic Recording (Seagate Technology), IEEE Magnetic Society Summer School (2003) 4. S. Tehrani, E. Chen, M. Durlam, M. DeHerrera, J. M. Slaughter, J. Shi and G. Kerszykowski, Journal of Applied Physics 85 (8), 5822-5827 (1999). 5. S. X. Wang, A. M. Taratorin, Academic, New York (1999). 6. R. M. White, IEEE Press, New York (1985). 7. Hitachi Global Storage Technologies (2004). 8. M. H. Kryder and R. W. Gustafson, Journal of Magnetism and Magnetic Materials 287 (0), 449-458 (2005). 9. Hitachi Global Storage Technologies (2005). 10. K. W. Wierman, T. J. Klemmer, B. Lu, G. Ju, K. J. Howard, A. G. Roy and D. E. Laughlin, Journal of Applied Physics 91 (10), 8031-8033 (2002). 11. G. Choe, M. Zheng, E. N. Abarra, B. G. Demczyk, J. N. Zhou, B. R. Acharya and K. E. Johnson, Journal of Magnetism and Magnetic Materials 287 (0), 159-166 (2005). 12. B. R. Acharya, J. N. Zhou, M. Zheng, G. Choe, E. N. Abarra and K. E. Johnson, Magnetics, IEEE Transactions on 40 (4), 2383-2385 (2004). 13. H. S. Jung and W. D. Doyle, Magnetics, IEEE Transactions on 39 (2), 679-684 (2003). 14. X. Min, B. Wilson, K. Takano, D. Hoa, Y. Ikeda and H. Rosen, Magnetics, IEEE Transactions on 41 (10), 3154-3156 (2005). 15. 16. S. Chikazumi, in Physics of Ferromagnetism Clarendon, Oxford, 635 (1997). S. Charap, L. Pu-Ling and H. Yanjun, Magnetics, IEEE Transactions on 33 (1), 978-983 (1997). 17. J. G. Zhu, materialstoday July/August, 22 (2003). 18. O. H. Robert C, Modern magnetic materials: principles and applications John Wiley & Sons, New York (2000). 19. H. N. Bertram, Theory of Magnetic Recording, Cambridge, Cambridge University Press (1994). 20. H. J. Richter, Journal of Magnetism and Magnetic Materials 321 (6), 467-476 (2009). 21. 22. H. Gavrila, Proceedings of the Romanian Academy, Series A 11, 41-46 (2010). T. Schrefl, M. E. Schabes, D. Suess and M. Stehno, Magnetics, IEEE Transactions on 40 (4), 2341-2343 (2004). 23. H. J. Richter, Journal of Physics D: Applied Physics 40 (9), R149 (2007). 24. Y. Wu, Encyclopedia for Nanoscience and Nanotechnology 7, 493 (2003). 25. J. Lohau, A. Moser, C. T. Rettner, M. E. Best and B. D. Terris, Magnetics, IEEE 141 Transactions on 37 (4), 1652-1656 (2001). 26. S. Sun, C. B. Murray, D. Weller, L. Folks and A. Moser, Science 287 (5460), 1989-1992 (2000). 27. S. R. Hubert A, in Magnetic Domains, The Analysis of Magnetic Microstructures (Springer, Berlin, 1998). 28. M. Nagao, Y.-G. So, H. Yoshida, M. Isobe, T. Hara, K. Ishizuka and K. Kimoto, Nature Nano (5), 325-328 (2013). 29. I. Manke, N. Kardjilov, R. Schäfer, A. Hilger, M. Strobl, M. Dawson, C. Grünzweig, G. Behr, M. Hentschel, C. David and e. al., Nature Communication 1, 125 (2010). 30. M. Kronseder, M. Buchner, H. G. Bauer and C. H. Back, Nature Communication 4, 2054 (2013). 31. C. A. Ross, Annual Review of Materials Science 31, 203-235 (2001). 32. G. C. Hadjipanayis, Journal of Magnetism and Magnetic Materials 200 (1–3), 373-391 (1999). 33. A. H. Morrish, The Physical Principle of Magnetism, John Wiley & Sons, inc. New York, London, Sydney (1965). 34. S. A. D’yachenko, V. F. Kovalenko, B. N. Tanygin and A. V. Tychko, Phys. 35. A. P. Ramirez, in Handbook of Magnetic Materials 13, 423 (2001). 36. J. Li, S. Zhang, J. Bartell, C. Nisoli, X. Ke, P. E. Lammert, V. H. Crespi and P. Solid State 50 (1), 32-42 (2008). Schiffer, Physical Review B 82 (13), 134407 (2010). 37. R. F. Wang, C. Nisoli, R. S. Freitas, J. Li, W. McConville, B. J. Cooley, M. S. Lund, N. Samarth, C. Leighton, V. H. Crespi and P. Schiffer, Nature 439 (7074), 303-306 (2006). 38. S. Ladak, D. E. Read, G. K. Perkins, L. F. Cohen and W. R. Branford, Nature Physics (5), 359-363 (2010). 39. X. Ke, J. Li, S. Zhang, C. Nisoli, V. H. Crespi and P. Schiffer, Applied Physics 40. Y. Han, Physical Review E 80 (5), 051102 (2009). 41. J. Li, X. Ke, S. Zhang, D. Garand, C. Nisoli, P. Lammert, V. H. Crespi and P. Letters 93 (25), 252504-252503 (2008). Schiffer, Physical Review B 81 (9), 092406 (2010). 42. E. Mengotti, L. J. Heyderman, A. Fraile Rodríguez, A. Bisig, L. Le Guyader, F. Nolting and H. B. Braun, Physical Review B 78 (14), 144402 (2008). 43. E. Mengotti, L. J. Heyderman, A. Bisig, A. Fraile Rodriguez, L. Le Guyader, F. Nolting and H. B. Braun, Journal of Applied Physics 105 (11), 113113-113113-113114 (2009). 44. T. Thomson, G. Hu and B. D. Terris, Physical Review Letters 96 (25), 257204 (2006). 45. F. Luo, L. J. Heyderman, H. H. Solak, T. Thomson and M. E. Best, Applied Physics Letters 92 (10), 102505-102503 (2008). 46. H. Mizuseki, M. Ishihara, X. Hu and N. Ohta, Magnetics, IEEE Transactions on 32 (5), 4335-4337 (1996). 47. S. Khizroev, Y. Hijazi, N. Amos, R. Chomko and D. Litvinov, Journal of 142 Applied Physics 100 (6), 063907-063908 (2006). 48. J. Moritz, G. Vinai, S. Auffret and B. Dieny, Journal of Applied Physics 109 (8), 083902-083904 (2011). 49. M. Albrecht, G. Hu, A. Moser, O. Hellwig and B. D. Terris, Journal of Applied Physics 97 (10), 103910-103915 (2005). 50. A. Nissim, B. John, L. Beomseop, H. S. Meir, H. Bing, T. Yuan, H. Jeongmin, G. Davil, M. I. Rabee, C. H. Robert, L. Dmitri and K. Sakhrat, PLoS ONE (7) (2012). 51. A. Imre, G. Csaba, L. Ji, A. Orlov, G. H. Bernstein and W. Porod, Science 311 (5758), 205-208 (2006). 52. R. P. Cowburn and M. E. Welland, Science 287 (5457), 1466-1468 (2000). 53. D. A. Allwood, G. Xiong, C. C. Faulkner, D. Atkinson, D. Petit and R. P. Cowburn, Science 309 (5741), 1688-1692 (2005). 54. T. H. E. Lahtinen, K. J. A. Franke and S. van Dijken, Scientific Report (2012). 55. L. Chang, D. J. Frank, R. K. Montoye, S. J. Koester, B. L. Ji, P. W. Coteus, R. H. Dennard and W. Haensch, Proceedings of the IEEE 98 (2), 215-236 (2010). 56. C. S. Lent, P. D. Tougaw, W. Porod and G. H. Bernstein, Nanotechnology (1), 49 (1993). 57. C. Chappert, A. Fert and F. N. Van Dau, Nature Material (11), 813-823 (2007). 58. S. S. P. Parkin, M. Hayashi and L. Thomas, Science 320 (5873), 190-194 (2008). 59. B. D. Terris and T. Thomson, Journal of Physics D: Applied Physics 38 (12), R199-R222 (2005). 60. R. Sbiaa and S. N. Piramanayagam, Recent Patents on Nanotechnology (1), 29-40 (2007). 61. B. D. Terris, T. Thomson and G. Hu, Microsyst Technol 13 (2), 189-196 (2007). 62. A. Kikitsu, Journal of Magnetism and Magnetic Materials 321 (6), 526-530 (2009). 63. S. A. Macintyre, Magnetic Field Measurement, CRC Press LLC (1999). 64. M. PardaviHorvath, IEEE Transactions on Magnetics 32 (5), 4458-4462 (1996). 65. M. Hwang, M. Farhoud, Y. Hao, M. Walsh, T. A. Savas, H. I. Smith and C. A. Ross, Magnetics, IEEE Transactions on 36 (5), 3173-3175 (2000). 66. O. Hellwig, A. Berger, T. Thomson, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher and E. E. Fullerton, Applied Physics Letters 90 (16), 162516-162513 (2007). 67. D. Suess, T. Schrefl, S. Fahler, M. Kirschner, G. Hrkac, F. Dorfbauer and J. Fidler, Applied Physics Letters 87 (1), 012504-012503 (2005). 68. H. Uwazumi, T. Shimatsu and Y. Kuboki, Journal of Applied Physics 91 (10 I), 7095-7097 (2002). 69. M. L. Yan, R. Skomski, A. Kashyap, L. Gao, S. H. Liou and D. J. Sellmyer, Magnetics, IEEE Transactions on 40 (4), 2495-2497 (2004). 70. H. Nemoto, I. Takekuma, H. Nakagawa, T. Ichihara, R. Araki and Y. Hosoe, Journal of Magnetism and Magnetic Materials 320 (22), 3144-3150 (2008). 71. O. Hovorka, R. F. L. Evans, R. W. Chantrell, Y. Liu, K. A. Dahmen and A. 143 Berger, Journal of Applied Physics 108 (12), 123901-123907 (2010). 72. I. Tagawa and Y. Nakamura, Magnetics, IEEE Transactions on 27 (6), 4975-4977 (1991). 73. A. Berger, B. Lengsfield and Y. Ikeda, Journal of Applied Physics 99 (8), 08E705-706 (2006). 74. R. W. Chantrell, N. Walmsley, J. Gore and M. Maylin, Physical Review B 63 (2), 024410 (2000). 75. Thermal Conductive Bonding, Inc. Available: http://www.tcbonding.com/sputtering.html 76. Light Diffraction in Standard Research Telescopes. Available: http://7secretstocuringcancernow.us/rife-for-your-life.html 77. Atomic Force Microscopy. Available: http://en.wikipedia.org/wiki/Atomic_force_microscopy 78. Magneto-optic Kerr effect magnetometry and microscopy (MOKE). Available: http://www.physik.uni-kl.de/hillebrands/research/methods/magneto-optic-ke rr-effect-magnetometry-and-microscopy/ 79. Y. Chen, J. Ding, D. Jie, T. Huang, L. Siang Huei, S. Jianzhong, Z. Baoyu, K. Hnin, A. Chun Kit, H. Shengbin and B. Liu, Magnetics, IEEE Transactions on 46 (6), 1990-1993 (2010). 80. P. Krone, D. Makarov, T. Schrefl and M. Albrecht, Journal of Applied Physics 106 (10), 103913-103915 (2009). 81. T. W. Usherwood, G. D. W. Smith and R. A. D. Mackenzie, Journal of Magnetism and Magnetic Materials 162 (2–3), 383-390 (1996). 82. G. A. Bertero and R. Sinclair, Journal of Magnetism and Magnetic Materials 134 (1), 173-184 (1994). 83. T. Onoue, T. Asahi, K. Kuramochi, J. Kawaji, T. Osaka, J. Ariake, K. Ouchi, G. Safran and N. Yaguchi, Journal of Applied Physics 92 (8), 4545-4552 (2002). 84. P. F. Carcia, S. I. Shah and W. B. Zeper, Applied Physics Letters 56 (23), 2345-2347 (1990). 85. P. F. Carcia, Z. G. Li and W. B. Zeper, Journal of Magnetism and Magnetic Materials 121 (1–3), 452-460 (1993). 86. R. Sbiaa, C. Z. Hua, S. N. Piramanayagam, R. Law, K. O. Aung and N. Thiyagarajah, Journal of Applied Physics 106 (2), 023906-023905 (2009). 87. J. M. Shaw, H. T. Nembach, T. J. Silva, S. E. Russek, R. Geiss, C. Jones, N. Clark, T. Leo and D. J. Smith, Physical Review B 80 (18), 184419 (2009). 88. A. Berger, Y. Xu, B. Lengsfield, Y. Ikeda and E. E. Fullerton, Magnetics, IEEE Transactions on 41 (10), 3178-3180 (2005). 89. J. M. Shaw, S. E. Russek, T. Thomson, M. J. Donahue, B. D. Terris, O. Hellwig, 90. S. Jing, T. Zhu, M. Durlam, E. Chen, S. Tehrani, Y. F. Zheng and J. G. Zhu, E. Dobisz and M. L. Schneider, Physical Review B 78 (2), 024414 (2008). Magnetics, IEEE Transactions on 34 (4), 997-999 (1998). 91. Y. Zheng and J.-G. Zhu, Journal of Applied Physics 81 (8), 5471-5473 (1997). 92. D. Weller, A. Moser, L. Folks, M. E. Best, L. Wen, M. F. Toney, M. Schwickert, J. U. Thiele and M. F. Doerner, Magnetics, IEEE Transactions on 36 (1), 10-15 144 (2000). 93. W. Scholz, D. Suess, T. Schrefl and J. Fidler, Journal of Applied Physics 95 (11), 6807-6809 (2004). 94. S. Rachid, C. Z. Hua, S. N. Piramanayagam, R. Law, K. O. Aung and N. Thiyagarajah, Journal of Applied Physics 106, 023906 (2009). 95. W. F. Brown Jr, Reviews of Modern Physics 17 (1), 15-19 (1945). 96. A. Aharoni, Reviews of Modern Physics 34 (2), 227-238 (1962). 97. H. Kronmüller, K. D. Durst and G. Martinek, Journal of Magnetism and 98. J. M. Shaw, S. E. Russek, T. Thomson, M. J. Donahue, B. D. Terris, O. Hellwig, Magnetic Materials 69 (2), 149-157 (1987). E. Dobisz and M. L. Schneider, Physical Review B 78, 024414 (2008). 99. W. M. Li, Y. J. Chen, T. L. Huang, J. M. Xue and J. Ding, Journal of Applied Physics 109 (7), 07B758-753 (2011). 100. Y. J. Chen, T. L. Huang, S. H. Leong, S. B. Hu, K. W. Ng, Z. M. Yuan, B. Y. Zong, J. Z. Shi, S. K. Hendra, B. Liu and V. Ng, Journal of Applied Physics 105 (7), 07C105-103 (2009). 101. S. Okamoto, N. Kikuchi, T. Kato, O. Kitakami, K. Mitsuzuka, T. Shimatsu, H. Muraoka, H. Aoi and J. C. Lodder, Journal of Magnetism and Magnetic Materials 320 (22), 2874-2879 (2008). 102. R. Chuan-Bing and et al., Journal of Physics D: Applied Physics 43 (49), 495001 (2010). 103. R. Dittrich, Journal of Applied Physics 97 (10), 10J705 (2005). 104. J. M. Shaw, M. Olsen, J. W. Lau, M. L. Schneider, T. J. Silva, O. Hellwig, E. Dobisz and B. D. Terris, Physical Review B 82 (14), 144437 (2010). 105. P. Krone, Journal of Applied Physics 108 (1), 013906 (2010). 106. G. Hu, Journal of Applied Physics 95 (11), 7013 (2004). 107. A. Barman, Journal of Applied Physics 101 (9), 09D102 (2007). 108. J. M. Shaw, Journal of Applied Physics 101 (2), 023909 (2007). 109. G. C. Han, J. J. Qiu, L. Wang, W. K. Yeo and C. C. Wang, Magnetics, IEEE Transactions on 46 (3), 709-714 (2010). 110. I. Tagawa, Intermag FA-02 (2009). 111. W. M. Li, Y. Yang, Y. J. Chen, T. L. Huang, J. Z. Shi and J. Ding, Journal of Magnetism and Magnetic Materials 324 (8), 1575-1580 (2012). 112. Y. J. Chen, T. L. Huang, J. Z. Shi, J. Deng, J. Ding, W. M. Li, S. H. Leong, B. Y. Zong, H. Y. Y. Ko, S. B. Hu and J. M. Zhao, Journal of Magnetism and Magnetic Materials 324 (3), 264-268 (2012). 113. W. M. Li, X. L. Huang, J. Z. Shi, Y. J. Chen, T. L. Huang and J. Ding, Journal of Applied Physics 111 (7), 07B917-913 (2012). 114. E. C. Stoner and E. P. Wohlfarth, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 240 (826), 599-642 (1948). 115. R. Street,J. C. Woolley: Proceeding of the Physical Society, Section A 62, 562 (1949). 116. H. S. Jung, E. M. T. Velu, S. S. Malhotra, U. Kwon, D. Suess and G. Bertero, 145 Magnetics, IEEE Transactions on 43 (6), 2088-2090 (2007). 117. G. Choe, M. Zheng, B. R. Acharya, E. N. Abarra and J. N. Zhou, Magnetics, IEEE Transactions on 41 (10), 3172-3174 (2005). 118. T. Oikawa, M. Nakamura, H. Uwazumi, T. Shimatsu, H. Muraoka and Y. Nakamura, IEEE Transactions on Magnetics 38 (5 I), 1976-1978 (2002). 119. M. Zheng, B. R. Acharya, G. Choe, J. N. Zhou, Z. D. Yang, E. N. Abarra and K. E. Johnson, IEEE Transactions on Magnetics 40 (4 II), 2498-2500 (2004). 120. B. R. Acharya, Z. Min, G. Choe, Y. Mingjun, P. Gill and E. N. Abarra, Magnetics, IEEE Transactions on 41 (10), 3145-3147 (2005). 121. Y. Sonobe, D. Weller, Y. Ikeda, K. Takano, M. E. Schabes, G. Zeltzer, H. Do, B. K. Yen and M. E. Best, Journal of Magnetism and Magnetic Materials 235 (1–3), 424-428 (2001). 122. Y. Sonobe, H. Muraoka, K. Miura, Y. Nakamura, K. Takano, A. Moser, H. Do, B. K. Yen, Y. Ikeda, N. Supper and W. Weresin, Magnetics, IEEE Transactions on 38 (5), 2006-2011 (2002). 123. K. Yoshida, Y. Hirayama and M. Futamoto, Magnetics, IEEE Transactions on 37 (4), 1589-1591 (2001). 124. T. Thomson, B. Lengsfield, H. Do and B. D. Terris, Journal of Applied Physics 103 (7), 07F548-543 (2008). 125. M. P. Sharrock, Magnetics, IEEE Transactions on 26 (1), 193-197 (1990). 126. M. Ranjbar, S. N. Piramanayagam, S. K. Wong, R. Sbiaa and T. C. Chong, Applied Physics Letters 99 (14), 142503 (2011). 146 11. Appendix 11.1 List of publications (1) W. M. Li, Y. J. Chen, T. L. Huang, J. M. Xue and J. Ding*, “Calculation of individual bit island switching field distribution in perpendicular magnetic bit patterned media”, Journal of Applied Physics, 109, 97B758 (2011). (2) W. M. Li, X. L. Huang, J. Z. Shi, Y. J. Chen, T. L. Huang, and J. Ding*, “Angular dependence and temperature effect on switching field distribution of Co/Pd based bit patterned media”, Journal of Applied Physics, 111. 07B917 (2012). (3) W. M. Li, Y. Yang, Y. J. Chen, T. L. Huang, J. Z. Shi and J. Ding*, “Study of magnetization reversal of Co/Pd Bit patterned media by micro-magnetic simulation”, Journal of Magnetism and Magnetic Materials, 324, 1575 (2012). (4) H. Wang, W. M. Li, M. T. Rahman, H. B. Zhao, J. Ding, Y. J. Chen and J. P. Wang*, “Characterization of L1(0)-FePt/Fe based exchange coupled composite bit pattern media”, Journal of Applied Physics, 111, 07B914 (2012). (5) Y. J. Chen*, T. L. Huang, J. Z. Shi, J. Deng, J. Ding, W. M. Li, S. H. Leong, B. Y. Zong, H. Yu Yu Ko, S. B. Hua, J. M. Zhao, “Individual bit island reversal and switching field distribution in perpendicular magnetic bit patterned media”, Journal of Magnetism and Magnetic Materials, 324, 264 (2012). (6) W. M. Li, J. Z. Shi, W. K. Lim, J. Ding*, “Influence of bias voltage on switching behavior of CoCrPt-SiO2 perpendicular recording media”, Journal of Physics D: Applied Physics, 46, 185001 (2013). (7) W. M. Li, J. Z. Shi, W. K. Lim, J. Ding*, “The effect of capped layer thickness on switching behavior in perpendicular CoCrPt based coupled granular/continuous media”, Journal of Magnetism and Magnetic Materials, 340, 50 (2013). (8) W. M. Li, S. K. Wong, T. S. Herng, L. K. Yap, C. H. Sim, Y. J. Chen, J. Z. Shi, G. C. Han, J. Ding*, Magnetic islands with configurable domain structures via dipole-dipole interactions and their possible applications, ACSnano, to be submit. (9) X. L. Hong, M. Li, N. N. Bao, E. Peng, W. M. Li, J. M. Xue, J. Ding*, Synthesis of FeCo nanoparticles from FeO(OH) and Co3O4 using oleic acid as reduction agent, Journal of Nanoparticle Research, in press. 147 [...]... Imre47) 25 Fig.2.10 Comparison of conventional continuous media and bit patterned media (adopted from Hitachi Global Storage Technologies7) 26 Fig.2.11 (a) The size of square bits at areal densities of 100, 500, 1000, 10 000 Gbit/in2 for conventional continuous media, respectively; (b) bit patterned media for 10 Tbit/in2 27 Fig.2.12 Illustration of the origin of demagnetization field ... anisotropy constant Ku 105 Fig.7.12 (a) A schematic of head pole of 2013 product; (b) A schematic of multi-states bit patterned media compared with conventional granular media Multi-grains per bit in conventional granular media are replaced xx by one cluster consisting of three closely arranged non-uniform islands 106 Fig.7.13 Schematic of the configurable associative memory 108... longitudinal recording technology are presented first, followed by the discussions on the functions of various layers in the perpendicular recording media Critical issues in perpendicular recording media is also discussed At the end of this introduction, motivations and objectives of this thesis is outlined in order to improve recording density of recent perpendicular recording media 1.1 A brief background of. .. the read sensor This process is called information recording Fig 1.3 structures of conventional multigrain media (adopted from Hitachi Global Storage7) 1.2 Transition from longitudinal recording to perpendicular recording For decades, the hard drive industry has focused almost exclusively on a method called longitudinal magnetic recording to record data on hard disk However, longitudinal recording is... introducing of SUL in perpendicular recording media provides higher write field, allows applications of media of higher anisotropy constant and switching field If materials with higher anisotropy constant can be used as the recording media, smaller grains can be used as a recording medium to store information and therefore higher linear density could be achieved Besides, the amplitude of read-back... Structures of conventional multigrain media (adopted from Hitachi Global Storage7) 3 Fig.1.4 Overview of the longitudinal magnetic recording system and perpendicular magnetic recording system with a soft underlayer (adopted from Hitachi Global Storage9) 4 Fig.1.5 Typical layer structures of perpendicular recording media 6 Fig.1.6 Media Materials Options (bulk properties) as the recording... development of bit patterned media (BPM) has become one of the necessary requirements to meet the ever-growing demand for ultra-high recording densities of up to 50Tbit/in2 by theoretical predictions Co/ Pd multilayer, which demonstrates high perpendicular magnetic anisotropy with good squareness is one of the most favorable magnetic materials for BPM However, the patterning process results in a modification of. .. Shearing correction of a magnetization curve 28 Fig.2.14 Sheared magnetization loop for perpendicular recording media The introduction of intergranular exchange steepens the hysteresis curve 29 Fig.2.15 (a) Schematic of a single domain island bit switching under influence of dipole-dipole interaction from neighbouring bits Switching field of each individual island could vary due to increased or decreased... The basic principle for longitudinal and perpendicular recording techniques is nearly the same When the write head pole moves on the top of the media, it leaves behind a magnetization pattern In longitudinal recording, the magnetization pattern is "left" or "right" For perpendicular recording, this magnetization pattern is either "up" or "down" The material used in perpendicular recording is usually hard... magnetization of grains on the media The localized area of the media can be switched to one of the two fixed directions Each of the localized areas can be considered as one bit with partially exchange-coupled magnetic grains A transition or continuous magnetization between two bits corresponds to a "1" or "0", respectively, as bit cell in a conventional multigrain media shown in Fig 1.3 When the write head moves . Calculation of SFD in Co/ Pd based bit patterned media 133 9.1.4 Micromagnetic simulation of SFD in Co/ Pd based bit patterned media 134 9.1.5 Temperature and angular dependence of SFD in Co/ Pd BPM. 500, 1000, 10 000 Gbit/in 2 for conventional continuous media, respectively; (b) bit patterned media for 10 Tbit/in 2 . 27 Fig.2.12 Illustration of the origin of demagnetization field CALCULATION OF MAGNETIZATION REVERSAL OF CO/ PD BIT PATTERNED MEDIA 52 4.1 Introduction 52 4.2 Experimental Details 52 4.3 Results and discussions 53 4.3.1 Microstructures of continuous Co/ Pd