Investigations on advanced magnetic recording media 1

INVESTIGATIONS ON ION IMPLANTATION IN ADVANCED MAGNETIC RECORDING MEDIA NIKITA GAUR NATIONAL UNIVERSITY OF SINGAPORE 2012 INVESTIGATIONS ON ION IMPLANTATION IN ADVANCED MAGNETIC RECORDING MEDIA NIKITA GAUR B.Sc Electronics (Hons), Delhi University, India A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE AUGUST 2012 Acknowledgements Acknowledgements Firstly, I would like to express my deep and sincere gratitude to my supervisors Prof. Charanjit Singh Bhatia and Dr. S. N. Piramanayagam for their invaluable guidance, advice and counseling during my PhD candidature. It was an absolute pleasure and honor to conduct my research under their supervision. Their patience and assurance during times of difficulty will always be remembered. Special thanks always goes out to all my seniors from Sri Venkateswara College, Delhi University, New Delhi, for helping and guiding me during my initial days at National University of Singapore (NUS). I would also like to express my gratitude to all my colleagues and friends in the ISML and SEL labs for their invaluable help and friendship. Many thanks to the lab officer, Mr. Jung Yoon Yong Robert, for all his help during my stay in SEL. The experimental facilities provided to carry out this research work by the Data Storage Institute (DSI) are acknowledged. I am very thankful to Mr. Tan Hang Khume from DSI for all his help during my attachment with DSI. I would also like to thank Mojtaba, Shreya, Taiebeh, Ajeesh, Mridul and Aditi for their lovely friendship and support. I am also thankful to Dr. K.K.M. Pandey and Mr. Le Hong Vu, with whom I have had the privilege of working during my candidature. Over and above, I would like to acknowledge the support provided by NUS Grant No. R 263-000-465-112 and NRF-CRP 4-2008-06 (NUS Grant No. R 263-000-585281) for this work. Also, I am truly grateful to the National University of Singapore for the NUS scholarship. I would like to express my appreciation towards Mr. S.L. Maurer, Dr. R.W. Nunes and Mr. S.E. Steen from the IBM Thomas J. Watson Research Center, Yorktown I Acknowledgements Heights, NY for providing ion implantation facility and fruitful discussions during monthly teleconference meetings. Last but not least, I would like to thank my Mama, Papa, Dimpi, Nikki and Bikash for their endless love, inspiration and encouragement. I would like to thank Almighty God, who always showers His kindness to me at every moment of my life. A big heartfelt thank you to everyone! Nikita Gaur II Table of Contents Table of Contents ACKNOWLEDGEMENTS I TABLE OF CONTENTS . III ABSTRACT VII LIST OF TABLES . XII LIST OF FIGURES . XIII LIST OF PUBLICATIONS, PATENTS AND CONFERENCES XIX Publications in Peer-reviewed journals XIX Patents . XX Conferences XX LIST OF SYMBOLS XXI LIST OF ABBREVIATIONS XXV LIST OF EQUATIONS .XXIX CHAPTER . 1 INTRODUCTION 1.1 Background 1.2 Research Objectives . 1.3 Organization of Thesis . CHAPTER . MAGNETIC RECORDING: LITERATURE REVIEW . 2.1 History of Magnetic Recording . 2.2 Basic Magnetism 10 III Table of Contents 2.3 Magnetic Recording Media . 17 2.3.1 Longitudinal Magnetic Recording (LMR) 17 2.3.2 Perpendicular Magnetic Recording (PMR) . 18 2.4 Challenges Faced by PMR 20 2.4.1 Superparamagnetism . 21 2.4.2 Magnetic Recording Trilemma . 22 2.5 Future Magnetic Recording Technologies . 23 2.5.1 High Anisotropy Constant Material 23 2.5.2 Heat-Assisted Magnetic Recording (HAMR) . 27 2.5.3 Anisotropy Graded Media . 32 2.5.4 Bit Patterned Media (BPM) . 34 2.6 Ion Implantation 38 CHAPTER . 42 EXPERIMENTAL AND COMPUTATIONAL DETAILS . 42 3.1 Introduction 42 3.2 Samples Fabrication by Sputtering 42 3.3 Ion Implantation 48 3.3.1 Samples Processing by Ion Implantation 48 3.3.2 Simulation Using SRIM and TRIM 49 3.4 Nanoimprint Lithography (NIL) 55 3.5 Magnetic Characterization . 59 3.5.1 Magneto Optical Kerr Effect (MOKE) . 59 3.5.2 Alternating Gradient Field Magnetometer (AGFM) . 62 3.5.3 Magnetic Force Microscopy (MFM) . 66 3.6 Structural Characterization 69 3.6.1 X-Ray Diffraction (XRD) . 69 3.6.2 X-Ray Photoelectron Spectroscopy (XPS) . 71 3.6.3 Electron Microscope (EM) 73 3.7 Density Functional Theory (DFT) Calculations 77 CHAPTER . 82 ION IMPLANTATION IN MAGNETIC MEDIA: EFFECT OF DEPTH OF IMPLANTATION . 82 4.1 Introduction 82 4.2 Experimental Methods 84 IV Table of Contents 4.3 Effect of Implantation of Boron in the Recording Layer and Soft Underlayer of CoCrPt-SiO2 Media 87 4.3.1 Magnetic Properties . 89 4.3.2 Crystallographic Properties . 96 4.3.3 Depth Profile of the Layer Structure . 98 4.3.4 Microstructural Properties . 101 4.3.5 SRIM Calculations and Lateral Straggle . 102 4.4 Effect of Implantation of Argon in the Recording Layer and Soft Underlayer of CoCrPt-SiO2 Media 106 4.4.1 Magnetic Properties . 107 4.4.2 Crystallographic Properties . 113 4.4.3 Depth Profile of the Layer Structure . 114 4.4.4 Microstructural Properties . 116 4.4.5 SRIM Calculations and Lateral Straggle . 119 4.5 Summary . 123 CHAPTER . 125 ION IMPLANTATION IN MAGNETIC MEDIA : EFFECT OF MASS OF ION SPECIES 125 5.1 Introduction 125 5.2 Patterned Media Requirements 125 5.3 Experimental Details . 128 5.4 Magnetic Properties . 131 5.4.1 Hysteresis Loops . 131 5.4.2 Saturation Magnetization 135 5.4.3 First Order Reversal Curves (FORC) Study . 138 5.5 Crystallographic Properties 141 5.6 Calculated Lateral Range and Straggle . 143 5.7 Relation between Straggle and Exchange Interaction 144 5.8 Density Functional Theory Calculations (DFT) 147 5.9 Summary . 149 CHAPTER . 150 PATTERNED MEDIA FABRICATION . 150 6.1 Introduction 150 V Table of Contents 6.2 Experimental Methods 150 6.2.1 FePt Media Optimization 152 6.2.2 Ion Species and Dose Optimization 157 6.2.3 Hard Mask Fabrication 161 6.3 Characterization of Patterned Media 164 6.3.1 Magnetic Properties . 164 6.3.2 Crystallographic Properties . 167 6.3.3 Magnetic Domain Study 168 6.4 Summary . 169 CHAPTER . 171 GRADED MEDIA BY ION IMPLANTATION . 171 7.1 Introduction 171 7.2 Experimental Methods 172 7.3 Magnetic Properties . 176 7.3.1 Kerr Loops . 176 7.3.2 Switching Field Distribution . 179 7.3.3 Magnetic Domain Study 180 7.3.4 Thermal Stability Measurements 182 7.4 XPS Depth Profiles 185 7.5 Crystallographic Properties . 186 7.6 Summary . 188 CHAPTER . 190 CONCLUSION AND SUGGESTIONS FOR FUTURE WORK 190 8.1 Conclusions . 190 8.2 Suggestions for Future Work 193 BIBLIOGRAPHY 195 VI Abstract Abstract Hard disk drives (HDD) have become an integral part of our daily lives. As the areal density is approaching a few tera bits per square inch (Tbits/in2) and beyond, the conventional perpendicular magnetic recording (PMR) technique has started facing thermal instability issues. Graded media and bit patterned media (BPM) are considered two possible candidates which can push the areal density limit higher. In this thesis, ion implantation as a potential method to produce these media is studied. Bit patterned media have magnetic islands in a sea of nonmagnetic matrix, providing improved thermal stability of magnetization, in addition to providing lower noise, greater ease of writing information, etc. One of the main limitations with current techniques for patterned media fabrication is the need of planarization — a process by which the lithographically modified topography is flattened. A lot of research is ongoing to overcome these challenges. Ion beam modification is one approach, which can help to solve the planarization problem. In this method, ion implantation is done though a mask (hard mask) such that the implanted regions become nonmagnetic and masked regions retain their magnetism. However, in order to meet such a goal it is crucial to understand the role of the implantation conditions on the saturation magnetization and lateral straggle. The objective of this work is to understand and determine the ions and energies needed to meet such requirements for achieving high areal densities. One of the crucial requirements for patterned media fabrication by the ion implantation method is to be able to reduce the saturation magnetization to zero in the implanted regions so that no signal is detected from that region. The second most critical parameter is lateral straggle, in simpler terms, the diffusion of ions in the VII Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation compared to boron in the case of implantation in RL. In fact, the films have a positive nucleation field value. This refers to the further increase in magnetic softness and much higher reduction in the anisotropy energy of the magnetic grains in RL. It should be noted that the changes in Kerr rotation cannot be correlated with Ms as it is also dependent on optical properties of the media in addition to Ms. In order to further understand the changes, we carried out MFM, XRD, XPS and SRIM related studies. 4.4.1.2 Magnetic Domain Study Figure 4-17 and Figure 4-18 shows the MFM images of AC demagnetized samples, both unimplanted and those with implantations of argon in the RL and SUL. The MFM images of the as-deposited sample (unimplanted) and the ones implanted with a lower dose showed smaller magnetic clusters, while those implanted with the higher dose exhibited larger domains. The effect of argon implantation in SUL on the domain size was remarkably similar to the effect of implantation of boron in RL and SUL (Figure 4-4 and Figure 4-5). RL properties were changed even at high energy implantation because of the damage caused by the ions passing through RL. In the case of ion implantation at low dose, the grains and grain boundaries are not affected much. However, high-dose implantation leads to more damage, as would be discussed in Section 4.4.5, causing grains to move out of grain boundaries and hence increasing the exchange interaction between the neighboring grains. This will lead to bigger grain sizes. Here as well, the increase in domain size after implantation of high fluences might have been due to reduction in the saturation magnetization or disruption in the RL owing to the migration of lattice atoms in the lateral or vertical direction, resulting in an increase of Co concentrations in the grain boundaries, which 109 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation were previously non-magnetic. Therefore it is believed that the same mechanism has been followed. More discussion will be presented in the next chapter. As-deposited μm RL, 1011 ions/cm2 μm RL, 1016 ions/cm2 μm Figure 4-17 MFM on AC demagnetized as-deposited (unimplanted) sample and samples implanted with argon in RL with the doses of 1011 and 1016 ions/cm2. 110 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation As-deposited μm SUL, 1011 ions/cm2 μm SUL, 1016 ions/cm2 μm Figure 4-18 MFM on AC demagnetized as-deposited (unimplanted) sample and samples implanted with argon in SUL with the doses of 1011 and 1016 ions/cm2. 111 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation 4.4.1.3 Soft Underlayer (SUL) Magnetic Properties Since only the perpendicular component of magnetization was being measured, which was contributed by the recording layer from polar MOKE, no information can be correlated to any changes in the SUL properties. To study SUL independently, inplane hysteresis loop measurements using AGFM were carried out on samples implanted with argon at 150 keV. It was seen that low-dose implantation with argon did not change the coercivity of the SUL; however; at high doses, coercivity increased Magnetization (emu/cc) to 11.92 Oe for argon ions (Figure 4-19). Magnetic Field (Oe) Figure 4-19 In-plane loops of the granular media implanted with argon ions in the SUL at both the doses, 1011 and 1016 ions/cm2, respectively. One may also notice the reduction in saturation magnetization after implantation at high doses for both the ions. The results obtained for argon are very similar to what has been observed for boron implantation. However the change in Ms and Hc are much more prominent comparatively. 112 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation 4.4.2 Crystallographic Properties The hysteresis loop and MFM data indicated changes in the magnetic properties arising from the structurally induced changes. In order to understand and verify these effects, XRD and XPS investigations were carried out. Figure 4-20 showed the θ-2θ plot of the sample implanted with argon in RL and SUL. Intensity (a.u.) (a) RL (b) SUL θ- 2θ (deg) Figure 4-20 XRD θ-2θ scans of samples implanted with argon in RL and SUL with the doses of 1011 and 1016 ions/cm2. It was observed that at high dose implantation into the RL, the Ru and Co peaks merged. It should be noted that in the case of boron implantation, even though the Co peak shifted towards lower 2θ values, no merging of the two peaks was seen (Figure 4-8). With further implantation into SUL, both the peaks were observed and a little displaced towards the lower 2θ values, similar to the case of boron implantation in SUL. The shifting of both the peaks towards lower 2θ values indicated an increase in 113 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation lattice spacing. In order to examine the details of interlayer mixing at the RL and the SUL, XPS measurements were carried out. 4.4.3 Depth Profile of the Layer Structure Figure 4-21 and Figure 4-22 show the XPS depth profiles of the samples implanted with argon into the RL and SUL at both doses. Depth profile measurements of samples implanted with ions at low doses (1011 ions/cm2) in the RL and SUL showed no diffusion or intermixing at the interfaces and sharp interfaces were observed. However, when the implantation dose in the RL increased to 1016 ions/cm2, there appeared a significant intermixing of Co from the recording layer and Ru from the underlayer at the CoCrPt-SiO2/Ru interface as seen in Figure 4-21. Slight intermixing between the seed layer (Ta) and underlayer (Ru) at the Ru/Ta interface was also visible. In case of implantation in SUL at high dose very significant intermixing at the CoCrPt-SiO2/Ru interface and Ru/Ta interface was observed as seen in Figure 4-22. Also, it can be seen that the thin Ru layer which was coupling the two SULs antiferromagnetically vanished upon high-dose implantation of argon in SUL, indicating an increase in interlayer diffusion. The interlayer diffusion or mixing supports the XRD observations well. The mixing of Ru with Co at the CoCrPtSiO2/Ru interface, when implantation is done in RL, is expected to cause a shift in the peak position and possibly a merger of the two peaks as observed in XRD measurements as the lattice spacing in Ru is larger than that in Co (Figure 4-20a). Similarly, in addition to the shift in the Co peak position in XRD, the shift in the Ru peak towards lower 2θ values can be explained based on the intermixing at the Ru/Ta 114 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation interface (Figure 4-20b). The intermixing at the Ru/Ta interface will lead to an increase in the lattice constant of Ru due to a bigger lattice spacing in Ta compared to Ru. RL, 1011 ions/cm2 Co Ta Ru Atomic Percentage (%) C Co Pt RL, 1016 ions/cm2 Co Ru Co Ta Pt Sputter Depth (nm) Figure 4-21 XPS depth profiles of samples implanted with argon in RL with the doses of 10 11 and 1016 ions/cm2. It should be noted that during ion implantation two phenomena occurs simultaneously. In one case, lattice atoms migrate to the surface of the material due to displacement and collision in the lattice structure. This leads to swelling of the surface. In another case, due to high current or high exposure dose/fluence, the surface atoms are sputter etched during implantation. Here, based on XPS depth 115 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation profile it was seen that high dose implantation lead to sputter etching of the top carbon overcoat. Moreover, no change in RMS roughness was seen based on AFM measurements showing no need for extra planarization step. SUL, 1011 ions/cm2 C Ta Co Ta Atomic Percentage (%) Ru Si Co Ru O Pt SUL, 1016 ions/cm2 Co Si Ru Co Ta O Pt Ru Sputter Depth (nm) Figure 4-22 XPS depth profiles of samples implanted with argon in SUL with the doses of 1011 and 1016 ions/cm2. 4.4.4 Microstructural Properties To investigate the microstructural changes in the recording layer after high-dose implantation, cross-section HRTEM were done on samples implanted with argon at low (1011 ions/cm2) and high (1016 ions/cm2) doses. Figure 4-23 did not show amorphization of the recording layer as a result of high-dose implantation as FFT images (Figure 4-23f) of the recording layer still indicated the presence of the 116 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation crystalline texture. From Figure 4-23 (d, e), the presence of tiny bubbles was visible as a result of argon gas build-up. Also, it can be seen that samples which were implanted with low doses (Figure 4-23b) showed very sharp interfaces (shown by red line) of all the layers but at high doses (Figure 4-23 e), no sharp interfaces were visible between ruthenium and the recording layer. This indicated interlayer diffusion between ruthenium and the recording layer and supports the XPS observations. Planview TEM were also conducted to detect any increase in grain size as XRD, XPS and TEM indicated a lot of structural changes and interlayer diffusions. There was a slight increase in grain size observed at high doses as shown in Figure 4-24c. Figure 4-23 Cross-section TEM of samples implanted with argon in RL with the doses of 1011 and 1016 ions/cm2. 117 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation (a) (a)As-deposited As-deposited 10 nm 10 nm 6.05 1.2 nm 7.8 1.4 nm 10 2.5 nm 11 (b) (b)10 1011ions/cm ions/cm2 10 nm 10 nm 16 (c) (c)10 1016ions/cm ions/cm2 10 nm 10 nm Figure 4-24 Plan-view TEM on as-deposited samples and samples implanted with argon at 1011 and 1016 ions/cm2 doses. Even though only one grain cluster has been outlined, it can be seen that other grains are also coalescing to form a bigger cluster. The increase in grain size as seen in Figure 4-24 seems to be due to coalescing of a number of grains together. This 118 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation could be due to the straggling of ions laterally leading to movement of magnetic lattice atoms and hence coalescing of grain. This also supports the increase in exchange interaction observed in MFM studies. 4.4.5 SRIM Calculations and Lateral Straggle In order to understand the changes in magnetic and structural properties as a result of ion implantation, nuclear and electronic stopping powers have been calculated for boron and argon with energy based on SRIM-2008 simulation in the CoCrPt-SiO2 (RL) target. Figure 4-25 shows the stopping mechanism for argon implantation at various energies. Argon, being a heavier ion than boron, induced more defects in the recording layer due to the dominant nuclear stopping mechanism, causing a greater drop in coercivity. Figure 4-25 SRIM-2008 simulation of nuclear and electronic stopping powers of argon in recording media target with respect to implantation energy. 119 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation When argon implantation was done at low energy viz 37 keV (in RL), the nuclear stopping mechanism was highly dominant. With increasing energy, the electronic stopping increased and became comparable. Furthermore, from the damage profiles (Figure 4-26), it can be seen that argon produces about five times more damage compared to boron in the recording layer. The reduction in coercivity from 1900 Oe to 350 Oe in the case of argon implantation in RL at high dose can be explained by the defect formation due to the dominant nuclear stopping mechanism. Heavier ions induce more defects in the recording layer compared to lighter ions due to the dominant nuclear stopping mechanism, thus resulting in an increase in the ballistic mixing and leading to a sharper fall in coercivity for boron compared to argon. The fall in coercivity was more significant for argon implantation in RL when implantation was done in RL (low energy, 37 keV) compared to SUL (high energy, 150 keV). This can be explained based on the damage profile obtained from the argon implantation into RL and SUL (Figure 4-26). It was found that more vacancies and interstitials, and hence more defects, were created in RL when implantation was carried out in RL compared to SUL. Figure 4-27 compares the changes in coercivity of samples implanted with doses of 1016 ions/cm2 of boron and argon ions. From XRD, XPS, TEM and SRIM as discussed in the previous sections, changes in coercivity upon implantation in RL and SUL were understandable. From Figure 4-27, it can be seen that the change in coercivity was more pronounced for boron than that for argon with regard to implantation in SUL. 120 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation Glass substrate Tantalum SUL2 Ruthenium SUL1 Tantalum Ruthenium Recording Layer (ATOMS/ cm3) / (ATOMS/ cm2) Carbon (a) RL 0A Target Depth Glass substrate Tantalum SUL2 Ruthenium SUL1 Tantalum Ruthenium Recording Layer Carbon (b) SUL 900A Figure 4-26 Damage profiles obtained from TRIM calculation for argon implantation into RL and SUL. A change in the hysteresis loop, even though the implantation was carried out in the SUL, is indicative of structural changes such as the lateral migration of atoms taking place in the recording layer. The more pronounced changes caused by boron implantation can be explained based on the contribution of electronic stopping power. Having been implanted at high energy and being a lighter ion, boron contributes significantly to the defect formation due to electronic stopping. Since the maximum of electronic stopping was close to the surface, hence more damage was caused in the recording layer by boron compared to argon, thus accounting for the larger changes caused by boron. 121 Hc (Oe) Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation Figure 4-27 Coercivity versus ions species at 1016 ions/cm2 when implantation is done in the RL and SUL. Figure 4-28 shows the lateral range and straggle calculated using lateral distribution as previously done for boron as a function of energies of implantation of argon ions. Here, it was observed that the lateral range and straggle increased from 6.8 and 9.2 nm to 28.7 and 36 nm, respectively when the implantation energy was changed from 37 keV to 150 keV. This showed that the higher the energy, the higher would be the lateral straggle – similar to what has been previously seen in the case of Lateral range and straggle (nm) boron implantation (Figure 4-14b). Energy (keV) Figure 4-28 The lateral range and straggle plotted as a function of energy of implantation of argon ion. 122 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation An intriguing observation was seen when the lateral range and straggle data were extracted for implantation of boron and argon in RL as shown in Figure 4-29. It was observed that the lateral range and straggle decreased as the implanted species changed from boron to argon, most likely due to large mass difference. This meant that if the mass of ion species was increased, the lateral straggle would be reduced even further. This warranted further investigation on the effect of the mass of ion species to reduce the lateral straggle even further, which will be discussed in detail in Lateral range and straggle (nm) the next chapter (Chapter 5). Figure 4-29 The lateral range and straggle plotted as a function of ion species implanted. 4.5 Summary The granular CoCrPt–SiO2 perpendicular recording media implanted with boron and argon ions at various doses at different depths (corresponding to various energies) were investigated. Lower dose implantation did not produce any significant changes in the coercivity, irrespective of the implanted layer for both ions. However, a significant reduction in coercivity at a higher dose of 1016 ions/cm2 was observed, irrespective of the type of implanted species. The reduction in coercivity was more significant when the ions were implanted into the recording layer compared to the 123 Chapter Ion Implantation in Magnetic Media: Effect of Depth of Implantation case of implantation into the soft underlayer. This was explained based on damages obtained due to stopping mechanisms. Damage was not the only reason for change in coercivity. A high radiation-induced mixing was observed as evidenced by the XPS and TEM obtained from the samples. With implantation of different species either in the recording layer or in the soft underlayer, the domain size always increased. The lateral straggle declined as the energy of implantation was reduced. Furthermore, it was noticed that heavier mass argon abated the lateral straggle more than boron. 124 [...]... doses of 10 11 and 10 16 ions/cm2 11 3 Figure 4- 21 XPS depth profiles of samples implanted with argon in RL with the doses of 10 11 and 10 16 ions/cm2 11 5 Figure 4-22 XPS depth profiles of samples implanted with argon in SUL with the doses of 10 11 and 10 16 ions/cm2 11 6 Figure 4-23 Cross-section TEM of samples implanted with argon in RL with the doses of 10 11 and 10 16 ions/cm2... boron in SUL with the doses of 10 11 and 10 16 ions/cm2 10 0 Figure 4 -11 Cross-section TEM of samples implanted with boron in RL with the doses of 10 11 and 10 16 ions/cm2 10 2 Figure 4 -12 SRIM-2008 simulation of nuclear and electronic stopping powers of boron in recording media target with respect to implantation energy 10 3 Figure 4 -13 Damage profiles obtained from TRIM calculation... and 10 16 ions/cm2 11 0 Figure 4 -18 MFM on AC demagnetized as-deposited (unimplanted) sample and samples implanted with argon in SUL with the doses of 10 11 and 10 16 ions/cm2 11 1 Figure 4 -19 In-plane loops of the granular media implanted with argon ions in the SUL at both the doses, 10 11 and 10 16 ions/cm2, respectively 11 2 Figure 4-20 XRD θ-2θ scans of samples implanted with argon in RL and SUL with... Carbon overcoat keV Kilo electron volt HRTEM High resolution TEM XXVIII List of Equations List of Equations Equation 2 1 Equation for the magnetic field produced by an infinitesimal length of current-carrying wire at a distance, r 11 Equation 2 2 Equation defining magnetization, M 11 Equation 2 3 Equation defining magnetic induction, B 11 Equation 2 4 Equation for exchange energy between two spins 11 ... 11 7 Figure 4-24 Plan-view TEM on as-deposited samples and samples implanted with argon at 10 11 and 10 16 ions/cm2 doses 11 8 Figure 4-25 SRIM-2008 simulation of nuclear and electronic stopping powers of argon in recording media target with respect to implantation energy 11 9 Figure 4-26 Damage profiles obtained from TRIM calculation for argon implantation into RL and SUL 12 1... 10 7 XIV List of Figures Figure 4 -16 Kerr loops of samples implanted with argon in (a) RL (corresponding to energy of implantation, 37 keV) and (b) SUL (corresponding to energy of implantation, 15 0 keV) with the doses of 10 11 and 10 16 ions/cm2 10 8 Figure 4 -17 MFM on AC demagnetized as-deposited (unimplanted) sample and samples implanted with argon in RL with the doses of 10 11 and 10 16 ions/cm2... 69 Equation 3 10 Scherrer Formula for Crystallite measurement from Rocking curve 70 Equation 3 11 Photoelectric equation 71 Equation 3 12 Rayleigh criterion in electron microscope 74 Equation 3 13 Total energy of a cluster which is a functional of 77 size XXIX List of Equations electron density ρ(r) Equation 3 14 Electron density expressed via one-electron wave function Φi(r) 78 Equation 3 15 Kohn-Sham... MFM on AC demagnetized as-deposited (unimplanted) sample and samples implanted with boron in RL with the doses of 10 11 and 10 16 ions/cm2 93 Figure 4-5 MFM on AC demagnetized as-deposited (unimplanted) sample and samples implanted with boron in SUL with the doses of 10 11 and 10 16 ions/cm2 94 Figure 4-6 In-plane loops of the granular media implanted with boron ions in the SUL at both the doses of 10 11. .. 14 0 Figure 5 -12 Hu plotted as a function of fluence for all the implanted species – 4He+, 12 C+, 14 N+, 40Ar+, 59Co+ and 12 1Sb+ 14 1 Figure 5 -13 XRD θ-2θ scan plotted as a function of fluence for all the implanted species – 4He+, 12 C+, 14 N+, 40Ar+, 59Co+ and 12 1Sb+ 14 2 Figure 5 -14 The lateral range and straggle as a function of ion species 14 4 Figure 5 -15 Correlation between... doses from 10 15 to 10 16 ions/cm2 18 7 Figure 8 -1 Steps in fabricating graded patterned media by means of ion implantation 19 4 XVIII List of Publications, Patents and Conferences List of Publications, Patents and Conferences Publications in Peer-reviewed journals 1 S Kundu, N Gaur, M S M Saifullah, H Yang and C S Bhatia, ‘Spacer-less, decoupled granular L10 FePt magnetic media using . 10 11 and 10 16 ions/cm 2 . 11 1 Figure 4 -19 In-plane loops of the granular media implanted with argon ions in the SUL at both the doses, 10 11 and 10 16 ions/cm 2 , respectively. 11 2. argon in RL and SUL with the doses of 10 11 and 10 16 ions/cm 2 . 11 3 Figure 4- 21 XPS depth profiles of samples implanted with argon in RL with the doses of 10 11 and 10 16 ions/cm 2 . 11 5. with argon in SUL with the doses of 10 11 and 10 16 ions/cm 2 . 11 6 Figure 4-23 Cross-section TEM of samples implanted with argon in RL with the doses of 10 11 and 10 16 ions/cm 2 . 11 7 Figure