CONTENTS Page No. Preface Chapter 1. Introduction 1.1. Evolution of Modem Magnetic Materials .................... .. '" ............... 01 1.2. Applications of magnetism ..................................... 04 1.3. Magnetic Composites... ............................... ........... 06 1.4. Ferrites ........................................................... '"...... 07 1.5. Magnetic Nanocomposites ....................................... 08 1.6. Rubber Ferrite Composites............... ....................... 09 Composites ...................................... 1.7. Present Study ....................................................... 10 Chapter 2. Theory and Materials 2.1. Different kinds of Magnetic ordering ........................ 13 2.1.1 Diamagnetism ................................................ 14 2.1.2 Paramagnetism ................................................ 15 2.1.3 Ferromagnetism Ferrornagnetism ............................................. 15 2.1.4 Antiferromagnetism........................................ 16 2.1.5 FerriInagnetism .............................................. 16 2.2. Important theories of Magnetism...... ...................... 16 2.2.1 Langevin theory of paramagnetism..................... paramagnetism .................... , 16 2.2.2 Weiss Molecular Field theory............................. 18 2.2.3 Exchange Interaction ........................................ 19 2.2.4 Neel's Two sublattice theorem ............................ 20 2.3. Superparamagnetism............................................ 23 2.4. Spinel ferrites. ferrites... . . . .... . . . . . . . . . . . . . ... . . . . . .. . . . . . . . . . . . . . . . . . . . . . . ... . .. 27 2.5. Electrical properties of spinel ferrites ........................ 29 2.6. Materials ............................................................ 30 2.6.1 Magnetic iron oxide .......................................... 30 2.6.2 Nickel Zinc ferri tes ............. . . . . . . . .. .. ......... .. . . . ........ .. ........... . . . ........ .. .. .. ...... .. .... 30 ferrites 2.6.3 Ion exchange resins ........................................... ............... .. ............... ........... 31 2.6.4 Natural Rubber Matrix ....................................... 32 Chapter 3. Experimental Techniques 3.1. Different schemes of preparation of magnetic nanocornposites "..................... nanocomposites ....... .. .................. 35 3.2. Preparation of nanocomposites by ion exchage method .............................. 36 method.............................. 3.3. Differential Scanning Calorimetry ............................ ..... ......... ... ........ . .. 37 3.4. Vibrating sample magnetometry.. .. . .. .... .. . ........... .. ...... ...... magnetometry................. .... 38 3.5. Iron Content Estimation ......................................... .. .. ...... " .... .. ...... ..... ............ 40 ....................... 3.6. Mossbauer Spectroscopy................. Spectroscopy ................................... ..... 40 3.7. ESR Spectroscopy. . . . ..... .. . ...... ....................................... . . . . . . .. .. .. . . . . .. . . . . . . ... . . . . . . .... 43 Spectroscopy .... '" 45 3.8. Preparation of ceramic nickel zinc ferrite samples .... ....... 3.9. Structural Evaluation of Ceramic NZF...................... 46 3.10. Incorporation of NhNh.xZn xZn xFe204 in natural rubber matrix...................... matrix ...................... 47 3.11. Cure Characteristics ............................................. ......... .................................... 49 3.12. Evaluation of hardness of the prepared RFCs ............. 50 3.13. Evaluation of Mechanical properties ........................ .............. .... ... ... 50 measurements.... .. ............... .. . .. .. ........ ... .. .. . ... . .. .. . ..... 51 3.14. Dielectric measurements ...... .............. measurements........... . ... .. . . .. .. .... 54 3.15. AC conductivity measurements .... ............................. Chapter 4. Effect of cycling on the magnetisation of magnetic nanocomposites and decomposition studies on the composites 4.1. Introduction ............................................... ......................................................... ... ....... 56 conditions............ ..... 57 4.2. Optimisation of the preparation conditions ... ... .... ..... ......................................................... 4.3. XRD studies ................................................. ........ 60 .................................................. .... ....... 65 4.4. Magnetic Studies ....................................... estimation... .. ..................................... 4.5. Fe Content estimation ............................... .. ......... 67 4.6. Moss Mossbauer studies ........................................ bauer studies" ....................... , ....... " .... .."........ ..... 67 ....................................................... 4.7. Conclusion ............................ .. ...... ..... .... .. ... .. .. ...,. 69 Chapter 5. Low Temperature studies on magnetic nanocomposites 5.1. Introduction........................................................... 70 5.2. Low temperature magnetisation studies..... ................ . .. 73 studies.... .................... 5.3. Mossbauer Studies ................................................ 74 5.4. ESR studies on the nanocomposites samples ............... 83 5.5. 5.5. Conclusion .......................................................... ...................... ..... ............................... 86 Chapter 6. Magnetic and Processability Studies on RFCs 6.1. Introduction ........................................................ 88 6.2. Structural Evaluation ............................................. 89 6.3. Cure Characteristics ......................................... ,..... 95 ............................................... 6.4. Magnetic Measurements ........................................ 98 6.4.1 Ceramic samples...................... samples ......... " ... .. . . . . . . ....................... . .. . .. . . ... .. . . . . . . . . . . 98 6.4.2 Composite samples .......................................... 100 6.4.3 Tailoring of magnetic properties ......................... 103 6.5. Conclusion ......................................................... 107 Chapter 7. Dielectric and Mechanical properties of RFCs 7.1. Introduction ......................................................... 109 7.2. Dielectric Measurements ......................................... ................................. ........ 110 7.2.1 Ceramic samples.......................... ............... .... 110 samples................................... .... ...... 7.2.2 Dielectric properties of Blank Natural rubber......... rubber.. ....... 117 7.2.3 Dielectric properties of RFCs ............. ................. '" ......... ..... 118 RFCs............. 7.3. Mechanical Properties ............................................ 125 7.4. Hardness Measurements ......................................... 127 7.5. Conclusion ........................................................... ..... ...................................................... 128 7.5. Chapter 8. AC conductivity studies on RFCs ......................................................... 8.1. Introduction .......... ..... ...... .. ............. ..................... 129 conductivity................. .. .... 130 8.2. Frequency dependence of AC conductivity........... 8.2.1 Ceramic samples ............................................. 130 8.2.2 Blank Natural rubber ....................................... 132 8.2.3 Composite samples .......................................... 133 ..................................... 8.3. Compositional dependence ......... ............................ 134 8.3.1 Ceramic Samples ............................................. 134 8.3.2 Composite samples .......................................... 135 8.4. Loading dependence ............................................. 136 8.5. Temperature dependence ....................................... 137 8.5.1 Ceramic Samples ............................................. 137 8.5.2 Blank Natural rubber ....................................... 139 8.5.3 Composite samples ................ , ......................... 139 .......................................... 8.6. Activation energy for conduction ............................. 141 8.7. Conclusion .......................................................... 142 Chapter 9. Summary and Conclusion ........ .................. 143 .... ...................... References Annexure I. Studies on the influence of dopants on the properties of maghemite (M.Phi! Dissertation work) Annexure n. 11. List of publications/communicated papers
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