LONG-RANGE AND SHORT-RANGE ORDERS, AND PHASE MISCIBILITY OF CoCrPt/Ti THIN FILMS SUN CHENGJUN (B. Eng. Liaoning Institute of Technology, P. R. China M. Eng. Dalian Railway Institute, P. R. China) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MATERIALS SCIENCE NATIONAL UNIVERSITY OF SINGAPORE 2004 Acknowledgements Acknowledgements I would like to express my heartfelt thanks to my thesis advisors, Associate Professors Gan-Moog Chow and Jian-Ping Wang, for their guidance, inspiration and encouragement throughout the course of my research. I have benefited from their expertise in all aspects of scientific research. I am grateful for their commitment in providing their student broad experience from which I will benefit in my future research. I deeply appreciate the advice and help from Mr. Eng-Wei Soo. His expertise helped me in my research. I also had invaluable help from Professor J. H. Je, Professor S. W. Han, Dr. Y. K. Hwu, and Professor D. Y. Noh. I would like to thank the faculty of the Department of Materials Science and the faculty fellow scholars of the Media and Materials groups, and Data Storage Institute. I would also like to thank Professor Zhensheng Shan, Ms. Siew It Pang, Ms. Shiaw Kee Chow, Dr. Lianjun Wu, and Mr. Daoyang Dai for their advice and kind assistance. Finally, I especially thank my wife, Ms. Minjie Liu, for her support, encouragement and sacrifice. i Contents Table of Contents Acknowledgements………………… …………………………………………….….i Summary ………………… ………………………………………………… ………vi List of Tables……… ………………………………………………… ………… .viii List of Figures ……… ……………………………………………… … .……… .ix List of Symbols ……… ……………………………………………… … .xii List of Abbreviations…………………………………………… … xiv I Introduction……………………… ……………………………………………….1 1.1 Media requirements for high areal density magnetic recording …… .……….2 1.2 1.3 1.1.1 Signal to noise ratio……………………………………………….2 1.1.2 Thermal stability ………………………………………………….3 1.1.3 Consideration of perpendicular magnetic recording………………4 General properties of perpendicular CoCrPt thin films………………………6 1.2.1 High magnetocrystalline anisotropy. ……………………………6 1.2.2 Effects of Cr on the saturation magnetization of CoCr …… ….6 1.2.3 Effects of Cr and Co phase segregation … .……… .………… 1.2.4 Effects of Pt on coercivity ………………………………… … .8 Research Aspects and objectives…… .….…………………………….… .9 1.3.1 Research Aspects ……………………………………………… 1.3.1.1 Research Aspect -1: NiP seedlayer… .… …… .…… 11 ii Contents 1.3.2 1.4 1.3.1.2 Research Aspect -2: Ti underlayer…… ……………….14 1.3.1.3 Research Aspect -3: Ti and CoCrPt interface……………18 1.3.1.4 Research Aspect -4: CoCrPt magnetic layer…………… 22 Objectives of this study…………………………………… .….31 Outline of the thesis………… ….…………………………………….… .32 II Experimental Techniques. ……………………… .……………….….…… 34 2.1 Sputtering…………….…………….………………………………… ………34 2.1.1 Introduction to sputtering. ……………………….…….……… …… 34 2.1.2 Sputtering fundamentals ………………………………………………35 2.1.3 Magnetron sputtering ………………………………………………….36 2.2 X-ray scattering. ………………………….…… …………….…………….…37 2.2.1 The Bragg Law …………….………………………………………….37 2.2.2 Reciprocal space geometry. ……………… …….……………………38 2.2.3 Powder diffraction ………….…………………………………………40 2.2.4 Mosaic distribution………………………………………………….…41 2.3 Extended x-ray absorption fine structure …………………………………… .42 2.3.1 Introduction to x-ray absorption fine structure………………….…… 42 2.3.2 Origin of EXAFS …………………………………………………… .43 2.3.3 Theory of EXAFS and SRO…….…………………………… ………44 2.4 Anomalous x-ray scattering ……………………………………………… .…48 2.4.1 Introduction to AXS…….…………………………………………… .48 2.4.2 Origin and theory of AXS……………….…………………………… 49 2.4.3 AXS measurement geometry …… .……………………………….….51 iii Contents 2.4.4 Comparisons of EXAFS and AXS…………………………………… 52 2.4.5 Phase miscibility and AXS ………….……………………………… .53 2.5 Vibrating sample magnetometer and alternating gradient force magnetometer.54 2.5.1 Vibrating sample magnetometer ……… .……….…….…………… 54 2.5.2 Alternating gradient force magnetometer……… …… .………… …55 III Effects of NiP Seedlayer on CoCrPt/Ti Thin Films …… .……… .…57 3.1 Sample preparation and characterizations …………………………….………57 3.2 Magnetic properties ….…… .……….………………….…………………….58 3.3 Structural characterization. ………………….………… .………….……… .60 3.4 Grain size and grain size distribution………………………………………… 63 3.5 Summary ………………………………………………………………………67 IV Interface Effects of CoCrPt/Ti Thin Films …………………………… 68 4.1 Sample preparation and characterizations .…… .………… …….………….68 4.2 Magnetic properties ……………………….………………………….……….69 4.3 Structural characterization by XRD ……………………………….…… .… .71 4.4 Structural characterization by TEM ………………………………………… .75 4.5 Summary …………………………………………… …………….……….…78 V Long-range and Short-range Orders, and Phase Miscibility of CoCrPt/Ti Thin Films …………………………………………… …… ….79 5.1 Sample preparation and characterizations.….………………………… .…….80 5.2 Magnetic properties …………………….…………………………………… 81 5.3 Long-range order of CoCrPt films …….…………….…………………… ….83 5.4 Short-range order of CoCrPt films ……………………………………….……86 iv Contents 5.5 Phase miscibility of CoCrPt films ……………………………………… .… 90 5.5.1 Anomalous x-ray scattering intensity and its measurements……… .…90 5.5.2 Phase miscibility of Cr in CoCrPt films……………………… .…… .93 5.5.3 Phase miscibility of Pt in CoCrPt films………………………….…… 96 5.5.4 Phase miscibility of Co in CoCrPt films………………………………100 5.6 Summary…………………………………………………………………… .101 VI Conclusions and Future Work ………… …………… ……………… 102 6.1 Conclusions ………………………………………………….…… .…… …102 6.2 Future work ……………………………………………………….………….103 References…………………….……………………………………….…………… 106 List of Publications……………………… ……………………….…………… 113 v Summary Summary In this thesis, the nanoscale layer engineering approaches, including the effect of NiP seedlayer on grain size and grain size distribution and the interface effect of CoCrPt/Ti thin films, were addressed. Furthermore, the long-range order (LRO) relationships between a CoCrPt magnetic layer and a Ti underlayer were investigated by using x-ray scattering. The short-range order (SRO), of Co, Cr, and Pt in CoCrPt films was studied by extended x-ray absorption fine structures (EXAFS). The phase miscibility of Co, Cr and Pt in crystalline CoCrPt (002) was analyzed by anomalous x-ray scattering (AXS). In order to achieve small and uniform grains and modify magnetic properties of CoCrPt films for high areal density magnetic recording, the effects of NiP seedlayer on the microstructure and magnetic properties of CoCrPt/Ti film were investigated. NiP was effective in reducing the grain size and improving the size distribution of the grains by enhancing the grain isolation of the layers deposited on top of it. A thin layer of NiP also improved the magnetic properties. The structure and interface of CoCrPt/Ti films were studied using x-ray scattering and transmission electron microscopy (TEM). At higher sputtering pressure, the lower kinetic energy of ions reduced their mobility and ability to mix with Ti, thus resulting in deposits on a well defined, abrupt interface. The roughness of the Ti surface promoted the growth of a more distinct columnar structure with small grain size and better isolation. The distinct columnar structure, with small and well-isolated CoCrPt grains, resulted in a decrease of exchange coupling between the vi Summary magnetic grains. The reduced exchange coupling contributed to the higher out-ofplane coercivity. It was concluded that the improved out-of-plane coercivity and squareness resulted from the combined effects of higher crystallinity and better texture of the CoCrPt (002) film, and increased interface roughness. The LRO and SRO and phase miscibility of CoCrPt/Ti films were investigated with synchrotron x-ray scattering, EXAFS and AXS. The crystallinity and texture of the CoCrPt magnetic layer followed the crystallinity and texture of the Ti underlayer that could be optimized. Improved magnetic properties resulted from the higher crystallinity and better texture of the CoCrPt (002), which was enhanced by the increased disorder of Cr and Pt at the grain boundaries. It was found that Cr and Pt were fully separated from the Co phase at the grain boundaries independent of the Ti underlayer. Direct evidence of Pt not being found within the Co lattice was given. vii List of Tables List of Tables Table 1.1 Lattice parameters of Co and Ti…………………………………………… 16 Table 1.2 Comparisons of different techniques for structural characterization………….27 Table 5.1 Fit parameters of both the first main peak around a Co absorber, fixing the S02=0.778 as in bulk Co, and the main peak around a Cr absorber, fixing the S02=0.824 as in bulk Cr. N, R and σ2 represent coordination number, distance, and Debye-Waller factor, respectively. (N=12 for the first shell of Co-foil, and N=8 for the first shell Cr-foil)…………………………… ……… ……… 87 viii List of Figures List of Figures Fig.1.1 The requirements of media materials for high-density magnetic recording…… Fig.1.2 Ms vs. Cr content for CoCr film. ………….………….…………….…………….7 Fig.1.3 Schematic graph of Co rich grain and Cr rich grain boundary……………………8 Fig.1.4 Structure of the CoCrPt/Ti/NiP media films ………….…………… .…………10 Fig.1.5 AFM images of CoCrPtTa/Cr/NiP and CoCrPtTa/Cr showing the surface topography….……………………………………………………………………12 Fig.1.6 Research Aspect -1: NiP seedlayer ………………………………………… 13 Fig.1.7 Road map of Research Aspect –1.………… ………… .……….………… …14 Fig.1.8 Research Aspect-2: Ti underlayer……….………… ………………………… 14 Fig.1.9 (a) A schematic diagram of the lattice planes of Si (111), Ag (111), Ti (0001), and Co (0001) viewed from Si and [111], and Co and Ti [0001] directions, every corner and center of the hexagonal lattice represent a given atom; (b) The designed structure of the thin films…… …………………… …………………16 Fig. 1.10 Scan spectra of x-ray pole figures. (a) {110} poles for single crystal Si (111); (b) {110} poles for Ag (111);(c){1,0, -1,1} poles for Ti (0002); and (d) {1,0, 1,1} poles for CoCrPt (0002)………………………………………………… 17 Fig.1.11 Road map of Research Aspect –2…………………………… .……………….18 Fig.1.12 Research Aspect-3: CoCrPt & Ti interface .…… .……………… .…… …. 19 Fig.1.13 Road map of Research Aspect –3………………………………… ……….….21 Fig.1.14 Research Aspect-4: CoCrPt magnetic layer .…………………………… … .22 Fig.1.15 Step model of alternating blocks of atomic planes of materials A and B, respectively………………………………………………………………… .24 Fig.1.16 A schematic diagram of individual contributions of Eq.1-6……….…… … 25 Fig.1.17 Conventional XRD and phase identification………………………………… .26 Fig.1.18 (a) XRD powder scans of Ni50Co50. (b) XRD powder scans of Ni90Co10…… .28 Fig.1.19 (a) AXS results of Ni50Co50 and Ni90Co10, Ni K-absorption edge. (b) AXS results of Ni50Co50 and Ni90Co10, Co K-absorption edge…………………………… .28 Fig.1.20 Metastable phase diagram of the Co-Cr system obtained when the sigma phase (σ) is not taken into account (full lines) and stable equilibrium phase diagram (dashed lines). Filled square from the sputtered film, hollow square from the bulk alloy. A miscibility gap between Co-rich hcp ferromagnetic phase (hcpf) and Co-poor hcp paramagnetic phase (hcpp) can be seen between 410 and 760 K……………………………………………………………………………… 30 Fig.1.21 Road map of Research Aspect –4…………………………… ………….….…31 Fig.2.1 Schematic diagram of sputter coating process………………………………… 35 Fig.2.2 Diffraction of x-ray by a crystal…………………………………………………37 Fig.2.3 The Ewald sphere construction in reciprocal space…………………………… .39 Fig.2.4 The accessible area (allowed reflections) shown in reciprocal space for a Cu single crystal with (111) surface using Cu Kα radiation, incident beam in (-1,1,0) plane………………………………………………………………… .…………40 Fig.2.5 The powder diffraction experiment. (a) Reciprocal space notation. The Ewald sphere (dash line) is fixed, and the lattice is rotated all angels about the origin. ix Chapter V LR and SROs, and phase miscibility of CoCrPt/Ti thin films 94) suggested further experimental work to confirm the assumption. To date, due to the experimental limit, the chemistry of Pt at the CoCrPt crystalline reflection is not known. In CoCrPt thin films, it is yet unclear whether Pt exists at Co crystalline reflections or segregates at the grain boundaries. The AXS spectra taken at APS of Pt of both films are depicted in Figure 5.13, indicating that no Pt was found at (002) reflection. Therefore Pt most likely also segregated at the grain boundaries. It was the direct evidence of Pt segregation in CoCrPt thin films. In order to pursue high precision of the experiments, we used a large slit and there was no Pt cusp at Pt energy scan. We also compared a large slit with a small slit during the AXS measurements; in either case there was no Pt at the (002) reflection. Since the global composition of Pt was 10 at. %, the lack of cusp was not due to the detection limit. It was confirmed that no Pt was found at Co (002) lattice, indicating that Pt was segregated. The segregation was independent of Ti underlayer thickness. The driving force for Pt separation is unclear; the possible interpretation of the phenomena observed is grain boundary segregation.95,96 The elemental miscibilities of grain boundary and grains are different; the solute elements are easier to be trapped at grain boundary rather than grains because it is energetically favorable for the solute to remain in the grain boundary. In particular, impurity elements often become very enriched at the grain boundaries. In the CoCrPt system, it was well known that Cr segregated at the grain boundaries. The grain boundaries have a more open structure compared with Co crystalline grains, allowing better accommodation of solute atoms (such as Pt) there rather than within the lattice. Since Pt is a relatively big element 98 Chapter V LR and SROs, and phase miscibility of CoCrPt/Ti thin films (atomic radius 1.39 Å and bonding radius 1.3 Å) compared with Co (atomic radius 1.25 Å and bonding radius .16 Å), Pt would likely segregate to grain boundary due to the large size misfit of Co and Pt. The Pt and Cr segregation at grain boundaries might play the role of pinning centers to impede domain wall motions, thus improving magnetic properties. 0.32 30 nm Ti underlayer Intensity (Counts/monitor) Co (002) 0.30 Pt LIII-edge 0.28 10 nm Ti underlayer 0.26 0.24 0.22 11.3 11.4 11.5 11.6 11.7 Photon Energy (keV) 11.8 Figure 5.13. AXS spectra of the (002) peak in the vicinity of Pt LIII- absorption edge. In summary, contrary to the traditional understanding, we found that Co and Pt were phase separated in the CoCrPt thin film. Furthermore, this study has also shown the first direct evidence of Pt segregation in these samples using AXS. 99 Chapter V LR and SROs, and phase miscibility of CoCrPt/Ti thin films 5.5.4 Phase miscibility of Co in CoCrPt films The spectra of AXS at Co-K edge (Fig. 5.14) showed deep cusps as expected, which agreed with the long-range order of CoCrPt films (Fig. 5.3). Combining the phase miscibility of Cr (Fig. 5.11) and Pt (Fig. 5.13) in CoCrPt films, and the SRO of Co (Fig. 5.6 and Table 5.1), it was reasonable to conclude that the CoCrPt (002) reflection consisted mainly of Co. This observation was also consistent with the previous NMR observation84 that indicated the Co-enriched component at the CoCr film contained mostly Co. The intensity difference of the two films attributed to the difference of the crystallinity of the films (Fig. 5.4). 0.020 Co (002) 30 nm Ti underlayer Intensity (Counts/monitor) 0.018 0.016 Co K-edge 0.014 0.012 0.010 10 nm Ti underlayer 0.008 0.006 7.5 7.6 7.7 7.8 7.9 8.0 Photon Energy (keV) Figure 5.14. AXS spectra of the (002) peak in the vicinity of Co absorption K-edge. 100 Chapter V LR and SROs, and phase miscibility of CoCrPt/Ti thin films Summarizing this section, the elemental chemistry of Co, Cr and Pt at Co (002) reflection was investigated using AXS. It was found that the textured Bragg peak consisting of mainly Co and Cr was segregated at the grain boundaries. In addition, contrary to the traditional understanding, the first direct evidence of Pt not found within the Co lattice was given, suggesting Pt was located at the grain boundaries. 5.6 Summary The long-range and short-range orders and phase miscibility of CoCrPt/Ti films were investigated with synchrotron x-ray scattering, EXAFS spectroscopy and AXS. The crystallinity and texture of the CoCrPt magnetic layer followed the crystallinity and the texture of the Ti underlayer. Improved magnetic properties resulted from higher crystallinity and better texture of the CoCrPt (002), which was enhanced by the increased disorder of Cr and Pt at the grain boundaries. It was found that Cr and Pt were segregated from the Co phase at the grain boundaries independent of the Ti underlayer. 101 Chapter VI Conclusions and future work Chapter VI Conclusions and Future Work The research work of this thesis is to obtain desired structural and magnetic properties of CoCrPt media film by nanoscale layer engineering approaches in order to satisfy the media requirements for high areal density magnetic recording, and to gain fundamental understanding of alloying and phase separation of the CoCrPt film and their correlations with magnetic properties by investigating the LRO, SRO and phase miscibility of CoCrPt /Ti thin films. 6.1 Conclusions The conclusions of this thesis include two parts. A: Nanoscale layer engineering approaches The NiP seedlayer was effective in reducing the grain size and improving the size distribution of grain by enhancing the grain isolation of the layers deposited on top of it. A thin layer of NiP also improved the magnetic properties. The enhanced out-of-plane coercivity and squareness resulted from the combined effects of higher crystallinity and better texture of the CoCrPt (002) film, 102 Chapter VI Conclusions and future work and increased interface roughness between CoCrPt and the Ti underlayer that could be influenced by sputtering pressure applied. B: LRO and SRO and phase miscibility of CoCrPt/Ti films The crystallinity and texture of the CoCrPt magnetic layer followed the crystallinity and texture of the Ti underlayer that could be optimized. Improved magnetic properties resulted from the higher crystallinity and better texture of the CoCrPt (002), which was enhanced by the increased disorder of Cr and Pt at the grain boundaries. It was found that Cr was segregated from the Co phase at the grain boundaries, independent of the Ti underlayer thickness. Direct evidence of Pt not being found within the Co lattice was given, suggesting that Pt was located at the grain boundaries. 6.2 Future work In nanostructured thin films of multiple elements, the formation of a solid solution or a composite depending on the miscibility of constituent elements, which may not follow the prediction of a conventional phase diagram that does not consider the interfacial and surface effects. For example, as discussed in Figure 1.20 and Figure 1.21, it has been shown that nanostructured NiCo films did not necessarily form a solid solution as expected from their phase diagram or suggested by the results of conventional XRD. Co was found in the (111) peak for Ni50Co50 film, but it did not 103 Chapter VI Conclusions and future work exist in this Bragg peak for Ni90Co10, indicating that Co and Ni was segregated and depended on the film composition.41 Another similar study indicated that the phase miscibility depended on the processing and other factors.65 The phase miscibility of nanostructured multiple elements thin films would depend on the processing, composition and other factors. As discussed in section 1.3.1.4, to date, little is known about the alloying and phase separation of the CoCrPt ternary thin films system due to the experimental limits. Our work of sputtered CoCrPt films demonstrated that the phase miscibility of constituent elements depended on the sputtering temperature and pressure. Although it is desirable to obtain the ternary CoCrPt phase diagram, however, such diagram requires work that is beyond the scope of this research. In this thesis, the LRO, SRO and phase miscibility of CoCrPt films with relatively better magnetic properties and potential application for perpendicular magnetic recording were investigated. The optimization of properties was achieved by varying the experimental conditions (such as processing, composition and other factors). A complete future study of the phase diagram of the CoCrPt ternary system is suggested. In addition, the magnetic contributions of Cr and Pt in CoCrPt media films need further studying using state-of-the-art experimental techniques such as x-ray magnetic circular dichroism (XMCD). For a magnetic material, XMCD arises due to the difference between the absorption of left and right circularly polarized x-rays. In x-ray absorption, the atom absorbs a photon, giving rise to the transition of a core electron to an empty state above the Fermi level. The absorption cross-sections are large, especially in the soft 104 Chapter VI Conclusions and future work x-ray range (500-2000 eV). The absorption edges have energies that are characteristic for each element and, due to the dipole selection rules, final states with different symmetries can be probed by choosing the initial state. By applying the total absorption and XMCD spectra, direct values for the orbital and spinning moment of the probed atom may be obtained. In this case, the magnetic contributions from Cr and Pt could be ascertained. 105 References References J. Hong, J. Kane, J. Hashimoto, M. Yamagishi, K. Noma and H. Kanai, in “The 12th Magnetic Recording Conference”, Minneapolis, (2001); Z. Zhang, in “Intermag Europe 2002”, Amsterdam, (2002). A. Moser, K. Takano, D. T. Margulies, M. Albrecht, Y. Sonobe, Y. Ikeda, S. Sun and E. E. Fullerton, J. Phys. D: Appl. Phys. 35, R157-R167 (2002). T. Shimatsu, H. Uwazumi, H. Muraoka, and Y. Nakamura, J. Magn. Magn. Mater. 235, 273 (2001). Y. Ikeda, Y. Sonobe, G. Zeltzer, B. K. Yen, K. Takano, H. Do, E.E. Fullerton, P. Rise, J. Magn. Magn. Mater. 235, 104 (2001). S. X. Wang and A. M. Taratorin, in “Magnetic Information Storage Technology”, Academic Press, USA, (1998). R. Wood, IEEE Trans. Magn. 36, 36 (2000). J. Mallison, IEEE Trans. Magn. 10, 368 (1974). K. E. Johnson, J. Appl. Phys. 87, 5365 (2000). R. Street, J. C. Woolley, Proc. Phys. Soc. A 62, 562 (1949). 10 S. H. Charrap, P. L. Lu, and Y. He, IEEE Trans. Magn. 33, 978 (1997). 11 S. Iwasaki, IEEE Trans. Magn. 16, 71 (1980). 12 S. Khizroev, Y. Liu, K. Mountfield, M. H. Kryder and D. Litvinov, J. Magn. Magn. Mater. 246, 335 (2002). 13 H. N. Bertram and M. Williams, IEEE Trans. Magn. 36, (2000). 14 S. Iwasaki, K. Ouchi, IEEE Trans. Magn. 14, 849 (1978). 106 References 15 D. Weller, A. Moser, L. Folks, M. E. Best, W. Lee, M. F. Toney, M. Schwickert, J. U. Thiele, M. F. Doerner, IEEE Trans. Magn. 36, 10 (2000). 16 J. G. Zhu, in “PhD Dissertation”, University of California at San Diego, 172 (1989). 17 W. Grogger, K. M. Krishnan, R. A. Ristau, T. Thomson, S. D. Harkness, and R. Ranjan, Appl. Phys. Lett. 80, 1165 (2002). 18 J. G. Zhu, in “PhD Dissertation”, University of California at San Diego, 163 (1989). 19 P. Glijier, J. Sivertsen, and J. Judy, J. Appl. Phys. 73, 5563 (1993). 20 A. Ishikawa, R. Sinclair, J. Magn. Magn. Mater. 152, 265 (1996). 21 K. M. Kemner, V.G. Harris, W. T. Elam, Y. C. Feng, D. E. Laughlin, J. C. Woicik, and J. C. Lodder, J. Appl. Phys. 82, 2912 (1997). 22 J. P. Wang, T. C. Chong, Datatech. 97 (2000). 23 L. L. Lee, D. E. Laughlin, and D. N. Lambeth, IEEE. Trans. Magn. 30, 3951 (1994). 24 L. Fang and D. N. Lambeth, Appl. Phys. Lett. 65, 3137 (1994). 25 E. N. Abarra, I. Okamoto, and Y. Mizoshita, in “Intermag 2000”, Canada, (2000). 26 D. Weller and M. F. Doerner, Annu. Rev. Mater. Sci. 30, 611 (2000). 27 T. Yamashita, L. H. Chan, T. Fujiware, and T. Chen, IEEE Trans. Magn. 27, 4727 (1991). 28 H. C. Tsai, M. S. Miller, and A. Eltoukhy, IEEE. Trans. Magn. 28,3093 (1992). 29 R. Ranjan, J. Chang, T. Yamashita, and T. Chen, J. Appl. Phys. 73, 5542 (1993). 30 Y. H. Lee, J. P. Wang, L. Lu, J. Appl. Phys. 87,6346 (2000). 107 References 31 S. I. Pang, J. P. Wang, E. W. Soo, T. C. Chong, IEEE Trans. Magn. 36, 2366 (2000). 32 J. J. K. Chang, Q. Chen, G. L. Chen, R. Sinclair, J. Appl. Phys. 81, 3943 (1997). 33 I. S. Lee, H. Ryu, H. J. Lee, and T. D. Lee, J. Appl. Phys. 85, 6133 (1999). 34 S. Iwasaki, Y. Nakamura, and K. Ouchi, IEEE Tran. Magn. 15, 1456 (1979). 35 H. Gong, M. Rao, D. E. Laughlin, and D. N. Lambeth, J. Appl. Phys. 85, 4699 (1999). 36 I. S. Lee, J. H. Koh, H. J. Lee, and T. D. Lee, ICIEC Trans. 80, 1174 (1997). 37 E. E. Fullerton, D. M. Kelly, J. Guimpel, I. K. Schuller, Y. Bruynseraede, Phys. Rev. Lett. 68, 859 (1992). 38 K. Meyer, I. K. Schuller, C. M. Falco, J. Appl. Phys. 52, 5803 (1981). 39 E. E. Fullerton, J. Pearson, C. H. Sowers, S. D. Bader, X. Z. Wu, S. K. Sinha, Phys. Rev. B. 48, 17432 (1993). 40 C. Michaelsen, Phil. Maga. A 72, 813 (1995). 41 G. M. Chow, W. C. Goh, Y. K. Hwu, T. S. Cho, J. H. Je, H. H. Lee, H. C. Kang, D. Y. Noh, C. K. Lin, W. D. Chang, Appl. Phys. Lett. 75,2503 (1999). 42 A. Pundt, C. Michaelsen, Phys. Rev. B 56, 14352 (1997). 43 K. Ouchi and S. Iwasaki, J. Appl. Phys. 57, 4013 (1985). 44 T. Chen, G. B. Charlan, and T. Yamashita, J. Appl. Phys. 54, 5103 (1983). 45 W. G. Haines, J. Appl. Phys. 55, 2263 (1984). 46 J. W. Smits, S. B. Luitjens, and F. J. A. den Broeder, J. Appl. Phys. 55, 2260 (1984). 47 H. H. Andersen, Nucl. Instrum. Meth. B 33,466 (1988). 108 References 48 J. George, in "Preparation of Thin Films", Marcel Dekker, New York, (1992). 49 D. L. Smith, in "Thin-Film Deposition", McGraw Hill, New York, (1995). 50 B. D. Cullity, in “Elements of X-ray Diffraction (2nd edition)”, Addison-Wesley, (1978). 51 D. K. Bowen and B. K. Tanner, in “High Resolution X-ray Diffractometry and Topography”, Taylor & Francis, London, (1998). 52 C. J. Sun, G. M. Chow and J. P. Wang, Appl. Phys. Lett. 82,1902 (2003). 53 H. Saisho and Y. Gohshi, in “Applications of synchrotron radiation to materials analysis”, Elsevier Health Sciences, Amsterd, (1996). 54 B. K. Argarwal, in “X-ray Spectroscopy: An Introduction”, Springer Verlag, Berlin, (1991). 55 W. Schweika, in “Disordered alloys: diffuse scattering and Monte Carlo simulations”, Springer Verlag, New York, (1997). 56 T. Ressler, J. Phys. IV 7, C2-269 (1997). 57 H. Stragier, J. O. Cross, J. J. Rehr, L. B. Sorensen, C. E. Bouldin, and C. E. Woicik, Phys. Rev. Lett. 69, 3064 (1992). 58 P. A. Lee, P. H. Citrin, P. Eisenberger, and B. M. Kincaid, Rev. Mod. Phys. 53, 769 (1981). 59 S. Foner, J. Appl. Phys, 79, 4740 (1996). 60 P. J. Flanders, J. Appl. Phys. 63, 3940 (1988). 61 E. W. Soo, J. P. Wang, C. J. Sun, Y. F. Xu, T. C. Chong and G. M. Chow, J. Magn. Magn. Mater. 235,93 (2001). 109 References 62 C. J. Sun, G. M. Chow, J. P. Wang, E. W. Soo, D. Y. Noh, J. H. Je and Y. K. Hwu, Nucl. Instr. Meth. B 199, 156 (2003). 63 C. J. Sun, G. M. Chow, J. P. Wang, E. W. Soo and J. H. Je, J. Appl. Phys. 93, 8725 (2003). 64 K. H. Muller, J. Vac. Sci. Technol. A 4, 184 (1986). 65 G. M. Chow, C. J. Sun, E. W. Soo, J. P. Wang, H. H. Lee, D. Y. Noh, T. S. Cho, J. H. Je, and Y. K. Hwu, Appl. Phys. Lett. 80, 1607 (2002). 66 C. W. Chen, J. Mater. Sci. 26, 1705 (1991). 67 B. E. Warren, in “X-Ray Diffraction”, Addison–Wesley, (1969). 68 C. J. Sun, G. M. Chow, E. W. Soo, J. P. Wang, Y. K. Hwu, T. S. Cho, J. H. Je, H. H. Lee, J. W. Kim, and D. Y. Noh, J. Nanosci. Nanotech. 1, 271 (2001). 69 S. I. Zabinsky, J. J. Rehr, A. Ankudinov, R. C. Albers, and M. J. Eller, Phys. Rev. B 52, 2995 (1995). 70 E. A. Stern, M. Newville, B. Ravel, Y. Yacoby, and D. Haskel, Physica B 209, 117 (1995). 71 J. J. Rehr, R. C. Albers, and S. I. Zabinsky, Phys. Rev. Lett. 69, 3397 (1992). 72 K. M. Kemner, V. G. Harris, W. T. Elam, Y. C. Feng, D. E. Laughlin, J. C. Woicik, and J. C. Lodder, J. Appl. Phys. 82, 2912 (1997). 73 H. Renevier, J. L. Hodeau, P. Wolfers, S. Andrieu, J. Weigelt, and R. Frahm, Phys. Rev. Lett. 78, 2775 (1997). 74 T. Bigault, F. Bocquet, S. Labat, O. Thomas, and H. Renevier, Phys. Rev. B 64, 125414 (2001). 75 Y. Maeda and M. Asahi, J. Appl. Phys. 61, 1972 (1987). 110 References 76 Y. Maeda and M. Takahashi, Jpn. J. Appl. Phys. Part 28, L248 (1989). 77 Y. Maeda and M. Takahashi, J. Appl. Phys. 68, 4751 (1990). 78 Y. Hirayama, M. Futamoto, K. Kimoto, and K. Usami, IEEE Trans. Magn. 32, 3807 (1996). 79 K. Hono, K. Yeh, Y. Maeda, and T. Sakurai, Appl. Phys. Lett. 66, 1686 (1995). 80 G. W. Qin, K. Oikawa, T. Ikeshoji, R. Kainuma, K. Ishida, J. Magn. Magn. Mater. 234, L1 (2001). 81 N. Inaba, T. Yamamoto, Y.Hosoe, M. Futamoto, J. Magn. Magn. Mater. 168, 222 (1997). 82 N. Inaba and M. Futamoto, J. Appl. Phys. 87,6863 (2000). 83 K. Hono, Y. Maeda, S. S. Babu, and T. Sakurai, J. Appl. Phys. 76, 8025 (1994). 84 D. J. Rogers, Y. Maeda, and K. M. Krishnan, J. Magn. Magn. Mater. 163, 393 (1997). 85 S. J. Kahng, Y. J. Choi, J. Y. Park, and Y. Kuk, Appl. Phys. Lett. 74, 1087 (1999). 86 T. Massalski, in “Binary Alloy Phase Diagram”, ASM International, Ohio, (1990). 87 F. Bolzini, F. Leccabue, R. Panizziieri, and L. Pareti, IEEE Trans. Magn. 20, 1625 (1984). 88 K. Barmak, R. A. Ristau, K. R. Coffey, M. A. Parker, and J. K. Howard. J. Appl. Phys. 79, 5330 (1996). 89 R. A. Ristau, K. Barmak, L. Henderson-Lewis, K. R. Coffey, J. K. Howard, J. Appl. Phys. 86, 4527 (1999). 90 C. R. Harp, D. Weller, T. A. Rabadeau, R. F. C. Farrow, and M. F. Toney, Phys. Rev. Lett. 71, 2493 (1993). 111 References 91 Y. Yamada, T. Suzuki, E. N. Abarra, IEEE Trans. Magn. 33, 3362 (1997). 92 T. A. Tyson, S. D. Conradson, R. F. C. Farrow and B. A. Jones, Phys. Rev. B 54, R3702 (1996). 93 P. W. Rooney, A. L. Shapiro, M. Q. Tran, and F. Hellman, Phys. Rev. Lett. 75, 1843 (1995). 94 M. R. Kim, S. Guruswamy, and K. E. Johnson, IEEE. Trans. Magn. 29, 3673 (1993). 95 J. L. Walter and K. Tangri, in “Structure and Property Relationships for Interface”, ASM International, Ohio, 43 (1991). 96 D. A. Porter, and K. E. Easterling, in “Phase Transformations in Metals and Alloys”, Van Nostrand Reinhold, New York, 136 (1981). 112 List of Publications List of Publications • Published (Source: ISI Citation Database) 1. C. J. Sun, J.P. Wang, E.W. Soo, and G.M. Chow “Effects of post-deposition annealing on structural properties of CoCrPt/Ti thin films”, Journal of Applied Physics, 95:7303 (2004). 2. C.J. Sun, G.M. Chow and J.P. Wang, “Epitaxial L10 FePt magnetic thin films sputtered on Cu (001)”, Applied Physics Letters, 82:1902 (2003). 3. C.J. Sun, G. M. Chow, J. P. Wang, E. W. Soo and J. H. Je, “Investigation of the crystallographic texture and interface roughness on CoCrPt/Ti magnetic thin films”, Journal of Applied Physics, 93:8725 (2003). 4. C. J. Sun, G.M. Chow, J.P. Wang, E.W. Soo, D.Y. Noh, J.H. Je and Y.K. Hwu, “A structural study of effects of NiP seed layer on the magnetic properties of CoCrPt/Ti/NiP perpendicular magnetic films”, Nuclear Instruments and Methods in Physics Research, B199: 156 (2003). 5. C.J. Sun, G.M. Chow, J.P. Wang, E.W. Soo, Y.K. Hwu, J.H. Je, T.S. Cho, H.H. Lee, D.Y. Noh, “Long-range order and short-range order study on CoCrPt/Ti thin films by synchrotron X-ray scattering and EXAFS”, Journal of Applied Physics, 91:7182 (2002). 6. G.M. Chow, C.J. Sun, E.W. Soo, J.P. Wang, H.H. Lee, D.Y. Noh, T.S. Cho, J.H. Je, Y.K. Hwu, “Structural study of CoCrPt films by anomalous x-ray scattering and extended x-ray absorption fine structure”, Applied Physics Letters, 80:1607 (2002). 7. C.J. Sun, G.M. Chow, Y.K. Hwu, E.W. Soo, J.P. Wang, T.S. Cho, J.H. Je, H.H. Lee, J.W. Kim and D.Y. Doh, “Structural effects of Ti underlayer on CoCrPt magnetic films”, Journal of Nanoscience and Nanotechnology, 1:271 (2001). 8. E.W. Soo, J.P. Wang, C.J. Sun, Y.F. Xu, T.C. Chong and G.M. Chow, “The Effects of NiP seed layer in Co-alloy perpendicular thin film media”, Journal of Magnetism and Magnetic Materials, 235:93 (2001). • To be submitted 1. C.J. Sun, Y. Zhao, Y.K. Hwu, J.P. Wang and G.M. Chow, “Structural study of thermal effects on Co-C multilayers films by x-ray absorption spectroscopy”, To be submitted. 113 [...]... and composition) with the magnetic properties, the fundamental correlation of LRO of the Ti underlayer and their effects on magnetic properties in the CoCrPt/ Ti system are not yet well understood In order to clarify the structural evolutions of the Ti underlayer and the CoCrPt magnetic layer, and to understand their relationship with magnetic properties, the effects of the LRO of Ti on the LRO of CoCrPt. .. thesis was a study of the long- range order and short -range order, and 1 Chapter I Introduction phase miscibility of CoCrPt/ Ti thin films In this chapter, we shall review the media requirements for high areal density magnetic recording, general properties of perpendicular CoCrPt thin films, and research aspects and objectives of this study At the end of this chapter, the outline of the thesis is given... density.2 Note that CoCr-based granular thin film was used in the first implementation of the perpendicular recording system.3,4 The correlations between structural and magnetic properties of magnetic thin films fall within the domain of materials science A better basic understanding of magnetic thin films, such as the degree of alloying and phase separation of these films, may provide a future guide for... CoCrPt films were studied as Research Aspect-2 (Fig 1-11) 17 Chapter I Introduction Research Aspect-2: Effects of LRO of Ti underlayer on the LRO of CoCrPt magnetic layer Structural properties (LRO) Crystallinity Mosaic distribution Magnetic properties Coercivity Squareness Relationship between LRO of Ti underlayer and CoCrPt magnetic layer Objective-2: To improve magnetic properties of CoCrPt films. .. Aspect-1 of this thesis was to study the effects of NiP seedlayer on the microstructure and magnetic properties of the CoCrPt/ Ti perpendicular films The objective was to develop small, uniform and isolated CoCrPt grains by inserting an additional NiP seedlayer The summary is shown in Figure 1.7 13 Chapter I Introduction Research Aspect-1: Effects of NiP seedlayer on CoCrPt/ Ti perpendicular thin films. .. (a) Out -of- plane coercivity and squareness as a function of Ar pressure, and (b) in-plane coercivity and squareness as a function of Ar pressure………………70 Fig.4.2 X-ray powder scans as a function of Ar pressure……….……………………….72 Fig.4.3 X-ray χ-rocking curve of the CoCrPt (002) peak as a function of Ar pressure…73 Fig.4.4 The integrated intensity of the powder scan and FWHM of χ rocking curve of the CoCrPt. .. of Research Aspect–2 The objective of this aspect was to improve the magnetic properties of CoCrPt films by improving their LRO Research Aspect-2 is summarized in Figure 1.11 1.3.1.3 Research Aspect-3: Ti and CoCrPt interface Research Aspect-3 of this thesis was the interface between CoCrPt and Ti (Fig 1.12) The following two parts are discussed: thin film growth kinetics and interface roughness; CoCrPt. .. -magnetic switching volume 24 σ-grain size distribution 25 τ- relaxation time 26 λ- wavelength 27 θ -the angle of the incidence and of the diffraction of the radiation relative to the reflecting plane 28 χ Co -Co elemental concentration at the specified Bragg reflection 29 χ Cr -Cr elemental concentration at the specified Bragg reflection 30 χ Pt -Pt elemental concentration at the specified Bragg reflection... is to relieve the lattice mismatch between the magnetic layer and the underlayer,24 and the antiferromagnetically coupled interlayer is to further modify magnetic properties by antiferromagnetically coupling the top with the bottom magnetic layers.25 It was reported that the structural and magnetic 9 Chapter I Introduction properties were significantly improved by inserting additional a seedlayer,23... Fig.5.1 (a) Coercivity as a function of Ti thickness…… …………………… ………81 Fig.5.1 (b) Squareness as a function of Ti thickness………… …….………………… 82 Fig.5.2 (a) Coercivity as a function of Ti thickness…… ………………………………82 Fig.5.2 (b) Hyeteresis loops of CoCrPt film with 30 nm Ti underlayer ………… 83 x List of Figures Fig.5.3 X-ray powder scans of the magnetic films with different thickness Ti underlayer, …………………………………………………………… . V Long- range and Short -range Orders, and Phase Miscibility of CoCrPt/ Ti Thin Films …………………………………………… …… ….79 5.1 Sample preparation and characterizations.….………………………… …….80 5.2 Magnetic. LONG- RANGE AND SHORT -RANGE ORDERS, AND PHASE MISCIBILITY OF CoCrPt/ Ti THIN FILMS SUN CHENGJUN (B. Eng. Liaoning Institute of Technology, P. R. China M. Eng. Dalian Railway Institute,. structural and magnetic properties of magnetic thin films fall within the domain of materials science. A better basic understanding of magnetic thin films, such as the degree of alloying and phase