Cation Substitution and magnetic properties of cubic spinel ferrite nanoparticles

CATION SUBSTITUTION PROPERTIES OF CUBIC

NANOPARTICLES

DEPARTMENT OF PHYSICS

INDIAN INSTITUTE OF TECHNOLOGY DELHI

CATION SUBSTITUTION AND MAGNETIC PROPERTIES OF CUBIC SPINEL FERRITE

NANOPARTICLES

SUNEETHA T

DEPARTMENT OF PHYSICS

INDIAN INSTITUTE OF TECHNOLOGY DELHI May 2017

AND MAGNETIC

SPINEL FERRITE

@ Indian Institute of Technology Delhi (IITD), New Delhi, 2017.

CATION SUBSTITUTION PROPERTIES OF CUBIC

NANOPARTICLES

Department of Physics

in fulfillment of the requirement

INDIAN INSTITUTE OF TECHNOLOGY DELHI

CATION SUBSTITUTION AND MAGNETIC PROPERTIES OF CUBIC SPINEL FERRITE

NANOPARTICLES

by

SUNEETHA T

Department of Physics

Submitted

in fulfillment of the requirements of the degree of Doctor of Philosophy to the

INDIAN INSTITUTE OF TECHNOLOGY DELHI MAY 2017

AND MAGNETIC SPINEL FERRITE

Doctor of Philosophy

Dedicated to My Husband

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CERTIFICATE

This is to certify that the thesis entitled

“

CATION SUBSTITUTION AND MAGNETIC PROPERTIES OF CUBIC SPINEL FERRITE NANOPARTICLES

”

being submitted by Ms. Suneetha T to the Department of Physics, Indian Institute of Technology Delhi, for the award of the degree of

‘Doctor of

Philosophy’

is a record of bonafide research work carried out by her. She has worked under our guidance and supervision and has fulfilled the requirements for the submission of the thesis, which in our opinion has reached the requisite standard.

The results contained in this thesis have not been submitted, in part or full, to any other University or Institute for the award of any degree or diploma.

Dr. Anurag Sharma Dr. Subhash C. Kashyap

Professor Former Professor

Department of Physics Department of Physics

Indian Institute of Technology Delhi Indian Institute of Technology Delhi

Hauz Khas, New Delhi-110016 Hauz Khas, New Delhi-110016

INDIA INDIA

Date: Date

ii

ACKNOWLEDGMENTS

First, I would like to thank to Almighty God for providing me the opportunity and strength to accomplish the present work.

It is an honor for me to express deep sense of profound gratitude and indebtedness towards my thesis advisor Professor S. C. Kashyap for his invaluable assistance, constant encouragement, generous advice, continuous support and inspiring guidance throughout my research work. His profound knowledge and idealistic approach have always been a constant source of inspiration to me. His guidance and support throughout this process has significantly shown effect on my life, both personally and professionally. His words have always inspired me and taken me to higher level of thinking.

I would like to express my thankfulness and gratefulness to my former joint supervisor Professor H. C. Gupta and present joint supervisor Professor Anurag Sharma for their support, cooperation and providing me all the help, whenever I needed. I am thankful to the Head, Department of Physics for providing the facilities in the Department/Institute. I am also grateful to all other professors of the department for their continuous support and guidance.

I am extremely grateful to Professor Sujeet Chaudhary for his timely help and fruitful discussions during my work.

I am very thankful to Professor S. K. Sharma of Hawaii Institute of Geophysics and Planetology, University of Hawaii (UH), Honolulu, for Raman spectroscopy characterization.

The help received from Indian Institute of Technology Bombay through SAIF facility for EPR (FMR) measurement and INUP facility for XPS investigation is gratefully acknowledged. The support from UGC-DAE CSR, Indore for Mössbauer measurements is also thankfully acknowledged.

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I would like to thank my colleague Manju Sharma and also take this opportunity to thank all my friends and well wishers especially Anitha, Swarna, Sridevi, Divya, Archana, Srinivas Ch, Satish K, Jeevan, Bhargav Ram, Bhargava Reddy for their continuous support.

Finally, I would express my gratitude to my parents and parents-in-law whose support and constant encouragement helped me throughout this program. Lastly, thanks to my dear husband for his continuous support and understanding, underpins my persistence to achieve higher academic goal and made the completion of this thesis possible. I express love to my son for his cooperation and being a source of motivation. This thesis could not have been completed without their unconditional support.

This work is financially supported by Indian Institute of Technology Delhi, New Delhi - 110016, India.

Suneetha Thota

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ABSTRACT

Manganese-zinc ferrite with certain substituents is known to have great application potential.

Structural, magnetic and electrical properties of these spinel ferrites depend upon their stoichiometry and cationic distribution among tetrahedral (A) and octahedral [B] interstitial sites in the O^2- anions sublattice. Very few studies are available on the comprehensive estimation of cation-distribution in Ni/Cu substituted Mn-Zn ferrite nanoparticles.

In the present work three series of MnxZn1-xFe2O4 (where x = 0.00, 0.35, 0.50, 0.65) and of Ni/Cu substituted Mn0.5Zn0.5Fe2O4 nanoparticleshave beensynthesized by citrate-gel method at low temperature (400 °C). All the samples have been analyzed for their structure, microstructure, distribution of cations in a unit cell and magnetic properties. Finally an attempt has been made to understand the cation distribution and magnetic property relationship. We report the structural, vibration, hyperfine and electronic-structure parameters

of single phase mixed spinel nanoparticles of

( ( )) . . ( ) where M = Ni, Cu and x = 0.05 -

0.45 with an aim to determine cation-distribution i.e. in these samples. All the relevant parameters are estimated by employing micro-Raman, Mössbauer, X-ray photoelectron spectroscopy, electron microscopy and X-ray diffraction method.

X-ray diffraction study reveals that Mn-Zn-Ni/Cu ferrite nanoparticles exhibit a single cubic mixed spinel phase. The Raman spectroscopy has established occupation of tetrahedral interstitial sites by certain cations, and Mössbauer spectra have shown that the cations (especially Fe) occupy both, tetrahedral and octahedral interstitial sites in the samples. The photoelectron spectra revealed valence state of the cations present at both the interstitial sites.

The best estimate of cation distribution in pristine and Ni/Cu substituted Mn-Zn ferrites has finally been made by reiteratively calculating the intensity ratios of various pairs of X-ray

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diffraction peaks (by using the cationic concentrations estimated by spectroscopic techniques) and matching with the observed intensity ratios of the same pair.

Rietveld-refined X-ray diffraction data has shown that the lattice parameter of Mn_xZn_1-xFe₂O₄ as well as of Ni/Cu substituted Mn_0.5Zn_0.5Fe₂O₄ nanoparticles varies in accordance with Vegard's law. Crystallite size of Mn_xZn_1-xFe₂O₄ nanoparticles decreases and strain increases with Mn content. However, Ni and Cu substitution for Mn in Mn0.5-xMxZ0.5F2O4 hasresulted in an improved crystallite size and crystalline order. The crystallite size of the synthesized nanoparticles lies in a narrow range of 7-13 nm. Scanning electron micrographs revealed the nanoparticles to be nearly spherical in shape with their average particle size lying below 25 nm for all the samples. HRTEM also supported the data of FESEM. The observed variation in structure parameters including mean ionic radii, tetrahedral and octahedral bond lengths, tetrahedral edge, shared and unshared octahedral edges and oxygen parameter has been explained on the basis of ionic radii of the substituent cations. This has also been employed to explain the variation in the observed Raman peaks.

Manganese substituted ZnFe2O4 (MnxZn1-xFe2O4 where x = 0.35, 0.50, 0.65) and Ni/Cu substituted Mn0.5Zn0.5Fe2O4 nanoparticles were superparamagnetic from room temperature down to blocking temperature (below which these were ferromagnetic). Thermo-magnetic (M-T) measurements have shown that the blocking temperature of MnxZn1-xFe2O4 enhances to a maximum of 150 K when x = 0.5. The Ni²⁺ substitution has enhanced the blocking temperature to 215 K and Cu²⁺ substitution for Mn cations in Mn_0.5Zn_0.5Fe₂O₄ to 300 K. The improvement in magnetization also followed similar trend, and exhibited a maximum value of magnetization (43 emu/g) for Mn_0.05Ni_0.45Zn_0.5Fe₂O₄ nanoparticles. Substantial enhancement in room temperature magnetization of substituted Mn-Zn ferrite nanoparticles is attributed to both, the modified cation-occupancy of the specific interstitial sites and increased ferrimagnetic fraction. Magneto-crystalline anisotropy of the nanoparticles, as

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estimated by Mössbauer and thermo-magnetic measurements, has decreased with increase in Ni/Cu substitution. The line widths (∆Hpp) of absorption peak and g- values are estimated from the FMR measurement made at 9.1 GHz. The Ni/Cu substitution in Mn-Zn ferrite has influenced the resonance properties and resulted in smaller line-widths (300-600) and higher g-values (2.02-2.21) most likely due to stronger exchange interaction and dipolar interaction The optimized substitution of nickel/copper for manganese in tetra-cationic Mn-Zn ferrite has improved their static and dynamic magnetic properties. These nanoparticles are expected to have great application potential for devices operating in high frequency region.

सार

कुछप्रकारकेपदार्थोंकेसार्थमैंगनीज-जस्ताफेराइटकोकाफीआवेदनक्षमताहै।इनस्स्पनलफेराइटकेस्रक्चरल, चुुंबकीयऔरइलेस्क्रकलगुणोंकोउनकेस्टेइइचीमेरीऔरटेराहेड्रल (ए) औरऑक्टेडियलकेबीच cationic ववतरण परननर्भरकरताहै [बी] O2- anions sublattice मेंअुंतरालीयसाइटें।नी / सीयूप्रनतस्र्थावपतएमएन-जेएनफेराइट नैनोकणोंमेंसेशन-ववतरणकेव्यापकअनुमानपरबहुतकुछअध्ययनउपलब्धहैं।

वतभमानकाममेंतीनप्रकारकी MnxZn1-xFe2O4 (जहाुंएक्स = 0.00, 0.35, 0.50, 0.65) औरनी / सीयू

प्रनतस्र्थावपतएमएन0.5 ज़्ने 0.5 फे 2 ओ 4 नैनोकणोंकमतापमान (400 डिग्रीसेस्ससयस) परसाइरेट-जेलववधध द्वारासुंश्लेवितककयागयाहै।।एकइकाईसेलऔरचुुंबकीयगुणोंमेंउनकेसुंरचना, माइक्रोस्रक्चर, सीमेंट्सके

ववतरणकेललएसर्ीनमूनेकाववश्लेिणककयागयाहै।आखिरकारकाशनववतरणऔरचुुंबकीयसम्पस्ततसुंबुंधको

समझनेकेललएएकप्रयासककयागयाहै।हमएकचरणलमधितस्स्पनलनैनोकणोंकेसुंरचनातमक, कुंपन, हाइपरफाइनऔरइलेक्रॉननकसुंरचनामानकोंकीररपोटभ〖(Zn〗 _δ 〖Mn〗 _γ 〖Fe〗 _ (1- (γ + δ))) [M_x

〖Zn〗 _ ( 0.5-δ) 〖एमएन〗 _ (0.5-γ-x) 〖फे〗 _ (1+ (γ + δ)) O_ (4) जहाुंएम = नी, क्यूऔरएक्स = 0.05 - 0.45 ननधाभररतकरनेकेउद्देश्यसेइननमूनोंमेंसेशन-ववतरणयानी δ और γ।सूक्ष्म-रमन, मॉसबॉयर, एक्स-रे

फोटोइलेक्रॉनस्पेक्रोस्कोपी, इलेक्रॉनमाइक्रोस्कोपीऔरएक्स-रेवववतभनववधधकाउपयोगकरकेसर्ीप्रासुंधगक मापदुंिोंकाअनुमानलगायागयाहै।

एक्स-रेवववतभनअध्ययनसेपताचलताहैककएमएन-जेएन-नी / क्यूफेराइटनैनोकैस्क्टक्सएकएकलघनलमधित मस्स्तष्कचरणकाप्रदशभनकरतेहैं।रमनस्पेक्रोस्कोपीनेकुछसुंधधयोंद्वाराटेराहेड्रलअुंतरालीयस्र्थलोंकाकब्जा

स्र्थावपतककयाहै, औरमॉसबॉयरस्पेक्रानेयहददिायाहैककनमूनोंमेंछुंदों (ववशेिरूपसे Fe), टेराहेड्रलऔर अक्शाइड्रलदोनोंतरहकीसाइटेंहैं।फोटोइलेक्रॉनस्पेक्रानेइुंटरस्स्टलशअलसाइटदोनोंपरमौजूददटप्पखणयोंके

अस्स्ततवअवस्र्थाकािुलासाककया।प्राचीनऔरनी / सीयूप्रनतस्र्थापनएमएन-जेएनफेराइटमेंसीशनववतरणका

सबसेअच्छाअनुमानअुंततःएक्स-रेवववतभनचोदटयों (स्पेसस्कोवपकतकनीकोंद्वाराअनुमाननत cationic साुंद्रता

काउपयोगकरके) औरलमलानकेववलर्न्नजोडेकीतीव्रताअनुपातकीपुनरावृस्ततगणनाद्वाराककयागयाहै।उसी

जोडीकेमनायागयातीव्रताअनुपात

ररएटवेसि-पररष्कृतएक्स-रेवववतभनिेटानेददिायाहैकक MnxZn1-xFe2O4 केसार्थसार्थनी / सीयूप्रनतस्र्थावपत Mn0.5Zn0.5Fe2O4 नैनोकणोंकेजालीपैरामीटरवेगािभकेकानूनकेअनुसारअलग-अलगहोतेहैं। MnxZn1- xFe2O4 नैनोकणोंकेकक्रस्टलीइटआकारएमएनसामग्रीकेसार्थघटजातीहैऔरतनावबढाताहै।हालाुंकक, Mn0.5-xMxZ0.5F2O4 मेंएमएकेललएनीऔरक्यूप्रनतस्र्थापनकेपररणामस्वरूपएकबेहतरकक्रस्टलीयआकार औरकक्रस्टलीयऑिभरहुआहै।सुंश्लेवितनैनोकणोंकाकक्रस्टलाइटआकार 7-13 एनएमकीएकसुंकीणभसीमामेंहै।

स्कैननुंगइलेक्रॉनमाइक्रोग्राफनेनैनोकणोंकोलगर्गसर्ीनमूनेकेललए 25 एनएमनीचेआतेहुएउनकेऔसत कणआकारकेआकारकेलगर्गगोलाकारहोनेकािुलासाककया।एचआरटीईएमनेएफईएसईएमकेआुंकडोंको

र्ीसमर्थभनददयाऔसतआयननकत्रिज्या, टेराहेड्रलऔरऑक्टैड्रलबाुंिकीलुंबाई, टेराहेिलककनारे, साझाऔरत्रबना

बाुंधाहुआऑक्र्थेडियलककनारोंऔरऑक्सीजनपैरामीटरसदहतसुंरचनामानकोंमेंमनायागयाववववधताको

अवयवोंके ionic radii केआधारपरसमझायागयाहै।मनायारमनचोदटयोंमेंलर्न्नताकोसमझानेकेललएयहर्ी

ननयोस्जतककयागयाहै।

मैग्नीजकेप्रनतस्र्थापन ZnFe2O4 (MnxZn1-xFe2O4 जहाुं x = 0.35, 0.50, 0.65) औरनी / सीयूप्रनतस्र्थावपत एमएन 0.5 ज़्ने 0.5 एफ 2 ओ 4 नैनोकणोंकमरेकेतापमानसेअवरुद्धतापमान (नीचेजोलोमधचककतसार्थे) केललए सुपरपेरामैग्नेदटकर्थे।र्थमो-चुुंबकीय (एम-टी) मापोंनेददिायाहैकक MnxZn1-xFe2O4 काअवरोधनतापमान अधधकतम 150 कश्मीरकोबढाताहैजब x = 0.5। Ni2 + प्रनतस्र्थापननेअवरोधकतापमानको 215 क्यूऔरकू 2 + Mn0.5Zn0.5Fe2O4-300 केमेंएमएनकेललएप्रनतस्र्थापनमेंबढायाहै।चुुंबकतवमेंसुधारनेर्ीइसीप्रकारकी

प्रवृस्ततकापालनककया, औरअधधकतमचुुंबकतव (43 ईएमयू / जी) काप्रदशभनककया Mn0.05Ni0.45Zn0.5Fe2O4 नैनोकणों।प्रनतस्र्थावपतएमएन-जेएनफेराइटनैनोकणोंकेकमरेकेतापमानचुुंबकतवमेंपयाभप्तवृवद्ध, दोनोंकेललए स्जम्मेदारहै, ववलशष्टमध्यवतीसाइटोंकीसुंशोधधतकदटऑन-अधधग्रहणऔरफेररमैग्नेदटकअुंशबढेहैं।मॉसबॉयर औरर्थमाभमो-चुुंबकीयमापकेअनुमानकेअनुसार, नैनोकणोंकीमैग्नेटो-कक्रस्टलीयअननसोरॉपीनी / सीयू

प्रनतस्र्थापनमेंवृवद्धकेसार्थघटगईहै। 9.2 गीगाहट्भजपरबनाएगएएफएमआरमापसेअनुमाननतचोटीऔरजी- मानकीरेिाचौडाई (Δ एचपीपी) काअनुमानहै।एमएन-जेएनफेराइटमेंनी / सीयूप्रनतस्र्थापननेप्रनतध्वननगुणों

कोप्रर्ाववतककयाहैऔरपररणामस्वरूपछोटेलाइन-चौडाई (300-600) औरउच्चतरजी-मान (2.02-2.21) केकारण मजबूतववननमयबातचीतऔरद्ववध्रुवीबातचीत

टेरा-सेटेननकएमएन-जेएनफेराइटमेंमैंगनीजकेललएननकल / ताुंबेकेअनुकूललतप्रनतस्र्थापननेअपनेस्स्र्थरऔर गनतशीलचुुंबकीयगुणोंमेंसुधारककयाहै।इननैनोकणोंकेउच्चआवृस्ततक्षेिमेंसकक्रयउपकरणोंकेललएशानदार आवेदनक्षमताहोनेकीसुंर्ावनाहै।

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TABLE OF CONTENTS

CONTENTS

^{P. No}

CERTIFICATE i

ACKNOWLEDGEMENTS ii

ABSTRACT iv

CONTENTS vii

LIST OF FIGURES x

LIST OF TABLES xv

Chapter 1: Introduction and Scope of Research Work

1.1Spinel Ferrites 1

1.2 Crystal Structure and Structural Parameters 5

1.3 Magnetic Behavior of Ferrites 8

1.3.1 Static Magnetic Properties 8

1.3.2 Superparamagnetism and Blocking Temperature 11

1.3.3 Dynamic Magnetization Properties (Ferromagnetic Resonance) 14 1.4 Magnetic Properties of Tetracationic Ferrites: Present Status 17

1.5 Objectives of the Research Work 20

1.6 Methodology and Thesis Plan 21

Chapter 2: Preparation and Measurement Techniques

2.1 Introduction 24

2.2 Sample Preparation by Sol-gel Method 25

2.3 Characterization Techniques 26

2.3.1 X-ray Diffraction (XRD) 26

2.3.1.1 Lattice Parameter and Crystallite Size 26

2.3.1.2 Intensity of Diffraction Lines and Cation Distribution 27 2.3.2 Field Emission Scanning Electron Microscopy (FESEM) 30

2.3.3 Transmission Electron Microscopy (TEM) 31

2.3.4 Raman Spectroscopy 33

2.3.5 Mössbauer Spectroscopy 36

2.3.6 X-ray Photoelectron Spectroscopy (XPS) 40

2.3.7 Static Magnetization Measurements 43

2.3.7.1 Physical Property Measurement System (PPMS) 43

viii

2.3.7.2 Vibrational Sample Magnetometry (VSM) 44

2.3.8 Dynamic Magnetization Measurement (Ferromagnetic Resonance) 46

Chapter 3: Structural and Microstructure Analysis

3.1 Introduction 49

3.2 Results and Discussion 49

3.2.1 Structural Analysis by X-ray Diffraction Method 49 3.2.1.1 Manganese Substituted ZnFe₂O₄ Nanoparticles 49 3.2.1.2 Nickel Substituted Mn_0.5Zn_0.5Fe₂O₄ Nanoparticles 52 3.2.1.3 Copper Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles 55

3.2.2 Micro-structural Analysis 57

3.2.2.1 Manganese Substituted ZnFe2O4 Nanoparticles 57 3.2.2.2 Nickel Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles 58 3.2.2.3 Copper Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles 60

3.3 Conclusions 61

Chapter 4: Cation Distribution and Structural Parameters

4.1 Introduction 62

4.2 Results and Discussion 63

4.2.1 Spectroscopic and X-ray Diffraction Data of Nickel Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles

64

4.2.1.1 Raman Spectra 64

4.2.1.2 Mössbauer Analysis 69

4.2.1.3 X-ray Photoelectron Spectroscopy 74

4.2.1.4 X-ray Diffraction Data 81

4.2.2 Cation Distribution and Structural Parameters of Nickel Substituted Mn_0.5Zn_0.5Fe₂O₄ Nanoparticles

82

4.2.2.1 Cation Distribution 82

4.2.2.2 Structural Parameters 84

4.2.3 Spectroscopic and X-ray Diffraction Data of Copper Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles

86

4.2.3.1 Raman Spectra 86

4.2.3.2 Mössbauer Analysis 88

4.2.3.3 X-ray Photoelectron Spectroscopy 89

4.2.3.4 X-ray Diffraction Data 93

ix

4.2.4 Cation Distribution and Structural Parameters of Copper Substituted Mn_0.5Zn_0.5Fe₂O₄ Nanoparticles

95

4.2.4.1 Cation Distribution 95

4.2.4.2 Structural Parameters 96

4.3 Conclusions 98

Chapter 5: Static Magnetic Properties

5.1 Introduction 101

5.2 Results and Discussion 101

5.2.1 Magnetic Study of Manganese Substituted ZnFe2O4 Nanoparticles 101 5.2.1.1 Isothermal Magnetization Investigation 101

5.2.1.2 Thermo-Magnetic Investigation 104

5.2.2 Magnetic Study of Nickel Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles 107 5.2.2.1 Isothermal Magnetization Investigation 107

5.2.2.2 Thermo-Magnetic Investigations 110

5.2.3Magnetic Study of Copper Substituted Mn_0.5Zn_0.5Fe₂O₄ Nanoparticles 113 5.2.3.1 Isothermal Magnetization Investigation 113

5.2.3.2 Thermo-Magnetic Investigations 116

5.3 Conclusions 118

Chapter 6: Dynamic Magnetic Properties

6.1 Introduction 120

6.2 Results and Discussion 120

6.2.1 Manganese Substituted ZnFe₂O₄ Nanoparticles 120 6.2.2 Nickel Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles 122 6.2.3 Copper Substituted Mn0.5Zn0.5Fe2O4 Nanoparticles 124

6.3 Conclusions 126

Chapter 7: Highlights, Major Outcome and Future Directions

7.1 Highlights 128

7.2 Major Outcomes 129

7.3 Scope of Future Work 135

APPENDIX 136

REFERENCES 139

LIST OF PUBLICATIONS 153

BIODATA 154

x

LIST OF FIGURES

Fig. 1.1 Temperature dependence of magnetic properties of a typical ferrimagnetic material (NiO.Fe2O3). The dashed curve in the figure represents corresponding data for metallic iron. 2 Fig. 1.2 Global share of soft magnetic material market segments, 2014 and 2019. ... 5 Fig. 1.3 The geometry of the occupied interstitial (A and B) sites in a spinel structure (showing half of a unit cell)³³. ... 6 Fig. 1.4 A cation at a tetrahedral site (A) is surrounded by 12 nearest cations, and a cation at an octahedral site (B) is surrounded by 6 nearest cations. ... 6 Fig. 1.5 The geometry of oxygen parameter (u) in a cubic spinel structure.³⁷ ... 7 Fig. 1.6 Tetrahedral and octahedral bond lengths (d_AL and d_BL), tetrahedral edge (d_AE) and shared and unshared octahedral edges (dBE and dBEU) in the sub-unit cell of a spinel ferrite ... 8 Fig. 1.7 Magnetic behavior of ferrimagnetic and superparamagnetic materials. ... 9 Fig. 1.8 Effect of substituting Zn cations for Mn, Co, and Ni in MO. Fe2O3 ferrites on saturation magnetization of the resulting ferrites (at 0 K).² ... 9 Fig. 1.9 (a) The possible high spin (HS) or low spin (LS) configuration of a d⁵ cation in an octahedral crystal field. (b)The crystal field splitting, ∆ (tet) and ∆ (oct) of the energy of five d orbitals in tetrahedral and octahedral crystal fields.³⁹ ... 11 Fig. 1.10 Variation of intrinsic coercivity (Hc) as a function of particle diameter (D) ⁴⁴. ... 12 Fig. 1.11 Typical magnetization (M) vs field (H) curves for superparamagnetic nanoparticles at different temperatures. ... 12 Fig. 1.12 Zero field cooled (ZFC) and field cooled warming (FCW) curves of magnetic nanoparticles. ... 13 Fig. 1.13 Precession of a magnetic dipole in the presence of a magnetic field. ... 15 Fig. 1.14 Energy level diagram for an electron with spin ½ in an applied magnetic field ... 15 Fig. 1.15 First derivative of an absorption peak exhibiting resonance field (Hr) and line width (∆H_pp). The inset corresponds to the absorption peak.⁴⁹ ... 16 Fig. 2.1 Flow Chart of sol-gel method for preparing substituted ferrite nanoparticles. ... 25 Fig. 2.2 Graphical representation of diffraction of X-rays from parallel atomic planes in a crystal. ... 26 Fig. 2.3 Williamson Hall plot for estimation of crystallite size (t) and strain (ε) ... 27 Fig. 2.4 Schematic diagram of Bragg Brentano Geometry employed for X-ray diffraction study of a powder specimen. ... 29 Fig. 2.5 Schematic diagram of field emission scanning electron microscope (FESEM). ... 31

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Fig. 2.6 Schematic ray diagram of working principle of a transmission electron microscope

(TEM). ... 32

Fig. 2.7 (a) Energy-level diagram showing the energy states involved in the scattering of radiation and (b) resulting (Raman) spectrum ... 33

Fig. 2.8 Raman active modes in a cubic spinel ferrite. ... 34

Fig. 2.9 (a) A block diagram of a Raman spectrometer and (b) schematic diagram of double- monochromator. ... 35

Fig. 2.10 A schematic diagram of nuclear process of ⁵⁷Co radioactive source in Mössbauer spectrometer. ... 36

Fig. 2.11 Working principle of a Mössbauer spectrometer ... 37

Fig. 2.12 The excited and ground state energy levels of ⁵⁷Fe and Mössbauer peak(s), due to surrounding electric or magnetic fields. (a) simple spectrum showing transmission vs the velocity of source relative to the absorber, (b) isomer shift caused due to different surroundings (c) the quadrupole splitting due to surrounding electric fields, and (d) magnetic splitting of the nuclear energy levels. ... 38

Fig. 2.13 Block diagram of Mössbauer experiment in transmission mode. ... 40

Fig. 2.14 Schematic diagram of an X-ray photoelectron spectrometer ... 42

Fig. 2.15 A schematic diagram of VSM assembly and inner view of the PPMS probe ... 44

Fig. 2.16 Schematic diagram of a vibrating sample magnetometer ... 45

Fig. 2.17 Basic configuration of an FMR spectrometer. The microwave bridge mainly consists of microwave generator, a circulator, and a detector. ... 47

Fig. 3.1 Rietveld refined powder X-ray diffractograms of Mn_xZn_1-xFe₂O₄ (x = 0.00, 0.35, 0.50, 0.65) nanoparticles. The figure includes experimental curves (black dots), calculated patterns (red line) and difference plots i.e. difference between experimental and calculated patterns (blue line). Bragg reflections (hkl) are indicated by vertical lines under each peak. 50 Fig. 3.2 Williamson Hall linear fit plots of X-ray data for MnxZn1-xFe2O4 (x = 0.00, 0.35, 0.50, 0.65) nanoparticles. ... 52

Fig. 3.3 Rietveld refined powder X-ray diffraction patterns of Mn0.5-xNixZn0.5Fe2O4 (x = 0.05, 0.15, 0.25, 0.35, 0.45) nanoparticles. The figure includes experimental curves (black dots), calculated patterns (red line) and difference plots i.e. difference between experimental and calculated patterns (blue line). Bragg reflections (hkl) are indicated by vertical lines. ... 53

Fig. 3.4 Williamson Hall linear fit plots drawn by using Bragg angles for different reflections for Mn_0.5-xNi_xZn_0.5Fe₂O₄ (where x = 0.05 - 0.45) nanoparticles... 54

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Fig. 3.5 Rietveld refined powder X-ray diffractograms of Mn_0.5-xCu_xZn_0.5Fe₂O₄ (where x = 0.05, 0.15, 0.25, and 0.35) nanoparticles. The figure includes experimental pattern (black dots), calculated pattern (red line) and difference curve between the two patterns (smooth green line) for each sample. The observed Bragg reflections (hkl) are indicated by vertical lines under each peak. ... 56 Fig. 3.6 Williamson Hall plots for samples having increased copper content in Mn0.5- xCu_xZn_0.5Fe₂O₄ (x = 0.05, 0.15, 0.25 and 0.35). ... 56 Fig. 3.7 FESEM micrographs for Mn_xZn_1-xFe₂O₄ nanoparticles (where x = 0.00(a), 0.35(b), 0.50(c), and 0.65(d). ... 58 Fig. 3.8 TEM micrographs for Mn0.5Zn0.5Fe2O4 nanoparticles revealing (a) average size of 14 nm, and (b) (311) planes in different crystallites with inter planar spacing of 2.34 Å. ... 58 Fig. 3.9 FESEM micrographs for Mn_0.5-xNi_xZn_0.5Fe₂O₄ (x =0.05, 0.15, 0.25, 0.35, 0.45) nanoparticles. Average particle size increases with Ni concentration in the nanoparticles. ... 59 Fig. 3.10 Transmission electron micrographs of Mn0.5-xNixZn0.5Fe2O4 (x = 0.05 and 0.25) nanoparticles revealing average size of 12 and 18 nm, respectively. The lattice planes in different crystallites are shown in the inset of the micrograph for x = 0.05. ... 59 Fig. 3.11 FESEM micrographs of Mn_0.5-xCu_xZn_0.5Fe₂O₄ (where x = 0.05, 0.15, 0.25 and 0.35) nanoparticles. ... 60 Fig. 4.1 Micro-Raman spectra (black curve which is superposed by the red curve) as function of wavenumber for MnxZn1-xFe2O4 (x = 0.00, 0.35, 0.50, 0.65) nanoparticles at room

temperature. 65

Fig. 4.2 Micro-Raman spectra (black curves) as a function of wave number for Mn_0.5-

xNi_xZn_0.5Fe₂O₄ (x = 0.05, 0.15, 0.25, 0.35, 0.45) nanoparticles. 67 Fig. 4.3 ⁵⁷ Fe Mössbauer spectrum (black) of Mn0.5Zn0.5Fe2O4 sample recorded at 5 K and at 5 Tesla. The red and green curves correspond to iron cations in tetrahedral (A) and octahedral

(B) coordination respectively 70

Fig. 4.4 ⁵⁷ Fe Mössbauer spectra (concealed black stars) of Mn0.5-xNixZn0.5Fe2O4 where x = 0.05, 0.15, 0.25, 0.35, 0.45 nanoparticles recorded at 5 K and at 5 Tesla. The blue and pink curves (sextets) correspond to iron cations in tetrahedral and octahedral coordination,

respectively. 72

Fig. 4.5 Effect of Ni substitution on a) Isomer shift (IS) b) Hyperfine field (Bhf) c) FWHM and d) Fe concentration (%) obtained from ⁵⁷ Fe Mössbauer spectra of Mn0.5-xNixZn0.5Fe2O4(x

= 0.05, 0.15, 0.25, 0.35, 0.45) samples. The squares and circles represent tetrahedral (A) and

octahedral (B) sites, respectively. 73

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Fig. 4.6 Deconvoluted XPS spectra of Fe 2p for different Ni substitution in (Mn_0.5-

xNi_xZn_0.5Fe₂O₄ x =0.05, 0.15, 0.25, 0.35) nanoparticles. The abbreviations Oct, Tetra and Sat stand for octahedral, tetrahedral and satellite, respectively. 77 Fig. 4.7 The XPS core level spectra of (a) Ni 2p and (b) Mn 2p3/2 in Mn0.5-xNixZn0.5Fe2O4 (x

=0.05, 0.15, 0.25, 0.35) nanoparticles. 78

Fig. 4.8 XPS spectra of Zn 2p3/2 in Mn0.5-xNixZn0.5Fe2O4 (x = 0.05, 0.15, 0.25, 0.35)

nanoparticles. 80

Fig. 4.9 Effect of Ni substitution in the Mn-Zn ferrite nanoparticles on (a) mean ionic radii of tetrahedral (rA) site and octahedral site (rB), (b) tetrahedral (dAL) and octahedral (dBL) bond lengths, (c) tetrahedral edge dAE, shared dBE, and unshared dBEU octahedral edges, and (d)

oxygen parameter ‘u’ 86

Fig. 4.10 Raman spectra (black curves) of Mn_0.5-xCu_xZn_0.5Fe₂O₄ (where x = 0.05, 0.15, 0.25 and 0.35) nanoparticles at room temperature. Red curve, nicely superimposing the black curve, corresponds to summation of the deconvoluted peaks in each case. 87 Fig. 4.11 ⁵⁷ Fe Mössbauer spectrum (curve in black) of Mn0.45Cu0.05Zn0.5Fe2O4sample recorded at 5 K and at 5 Tesla. The curves in blue and orange colors correspond to iron cations in tetrahedral (A) and octahedral (B) co-ordination respectively. 88 Fig. 4.12 Fe 2p core level energy peaks in the XPS spectrum of nanoparticles having different Cu concentration in Mn0.5-xCuxZn0.5Fe2O4 where x = 0.05, 0.15, 0.25 and 0.35. The deconvoluted sub-peaks establish the presence of Fe cations at both A and B interstitial sites.

90 Fig. 4.13 The XPS core level spectra: (a) Cu 2p and (b) Mn 2p c) Zn 2p_3/2 and d) O1s recorded from Mn_0.5-xCu_xZn_0.5Fe₂O₄ (x = 0.05, 0.15, 0.25 and 0.35) nanoparticles. 91 Fig. 4.14 Effect of Cu substitution in the Mn-Zn ferrite nanoparticles on (a) mean ionic radii of tetrahedral (rA) site and octahedral site (rB), (b) tetrahedral (dAL) and octahedral (dBL) bond lengths, (c) tetrahedral edge dAE, and (d) shared dBE, and unshared dBEU octahedral edges. 97 Fig. 5.1 M-H behavior for MnxZn1-xFe2O4 (where x = 0.00, 0.35, 0.50, 0.65) nanoparticles at

room temperature. 102

Fig. 5.2 M-H loops for MnxZn1-xFe2O4 (where x = 0.35, 0.50, 0.65) nanoparticles at 100 K.

The inset shows coercivity of the samples. 103

Fig. 5.3 Room temperature Mössbauer spectrum of Mn0.5Zn0.5Fe2O4 nanoparticles (a) experimental data and (b) simulated data along with experimental data 104 Fig. 5.4 M-T (FCW-ZFC) curves for Mn_xZn_1-xFe₂O₄ (x = 0.00, 0.35, 0.50, 0.65)

nanoparticles recorded at a field of 20 Oe. 105

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Fig. 5.5 ZFC curves for Mn_xZn_1-xFe₂O₄ (x = 0.00, 0.35, 0.50, 0.65) nanoparticles. 106 Fig. 5.6 M-H behavior of Mn_0.5-xNi_xZn_0.5Fe₂O₄ (x = 0.05, 0.15, 0.25, 0.35, 0.45) nanoparticles. The inset figure shows the coercivity of the samples. 108 Fig. 5.7 Room temperature Mössbauer spectra of (a) Mn0.45Ni0.05Zn0.5Fe2O4 and (b)

Mn0.05Ni0.45Zn0.5Fe2O4.nanoparticles 110

Fig. 5.8 M-T curves of Mn0.5-xNixZn0.5Fe2O4 (x = 0.05, 0.15, 0.25 and 0.35) nanoparticles

recorded at 20 Oe showing blocking temperature. 111

Fig. 5.9 M-H loops of Mn_0.5-xCu_xZn_0.5Fe₂O₄ (where x = 0.05, 0.15, 0.25 and 0.35) nanoparticles at room temperature. The insert shows small values of coercivity of the

samples. 114

Fig. 5.10 Arrott’s plots (M² vs H/M at room temperature) for Mn0.5-xCuxZn0.5Fe2O4 (where x

= 0.05, 0.15, 0.25 and 0.35) nanoparticles. 115

Fig. 5.11 Room temperature Mössbauer spectra of (a) Mn_0.45Cu_0.05Zn_0.5Fe₂O₄ and (b)

Mn0.25Cu0.25Zn0.5Fe2O4. 115

Fig. 5.12 Field cooled and zero field cooled (FCW-ZFC) curves for Mn0.5-xCuxZn0.5Fe2O4

(where x = 0.05, 0.15, 0.25, 0.35) nanoparticles recorded at a field of 50 Oe. 116 Fig. 6.1 (a) First derivative (dI/dH vs H) of resonance signals from Mn_xZn_1-xFe₂O₄(x = 0.00, 0.35, 0.50, 0.65) at microwave frequency of 9.1 GHz. (b) Variation of line- width (∆H_pp) and magnetization (M) with Mn concentration (x) in MnxZn1-xFe2O4nanoparticles. 121 Fig. 6.2 First derivative (dI/dH vs H) of ferromagnetic resonance signals from Mn0.5- xNixZn0.5Fe2O4 (x = 0.05, 0.15, 0.25, 0.35, 0.45) nanoparticles at microwave frequency of 9.1

GHz. 123

Fig. 6.3 First derivative (dI/dH) vs applied field (H) curves derived from the resonance signals from Mn0.5-xCuxZn0.5Fe2O4 nanoparticles where x = 0.05, 0.15, 0.25 and 0.35 recorded

at 9.1 GHz. 125

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LIST OF TABLES

Table 1.1 Magnetic and electrical properties of Mn-Zn and Ni-Zn ferrites ... 3 Table 1.2 Major industrial applications and desired parameters of spinel ferrites ... 4 Table 1.3 Arrangement of metal ions in the unit cell of cubic spinel ferrite. ... 6 Table 1.4 Ion distribution and net moment per molecule of certain ferrites and their solid solution ... 10 Table 1.5 The three series of mixed ferrite nanoparticles, investigated in the present work. 21 Table 2.1 Structure factors of different Bragg planes comprising of different ions in a ferrite ... 28 Table 2.2 Raman active vibration modes and frequencies in a cubic spinel ferrite ... 34 Table 3.1 Refinement parameters of X-ray powder diffraction data.¹¹³ ... 51 Table 3.2 The unit cell and refinement parameters of MnxZn1-xFe2O4 (where x = 0.00, 0.35, 0.50, 0.65) nanoparticles obtained from X- ray powder diffractograms ... 51 Table 3.3 Rietveld refinement parameters, crystallite size (t and D) and lattice parameter (a_exp) of Mn_0.5-xNi_xZn_0.5Fe₂O₄ where x = 0.05, 0.15, 0.25, 0.35, 0.45 nanoparticles. ... 55 Table 3.4 The unit cell and refinement parameters along with crystallite size (aexp in Ǻ, D and t in nm) of Mn0.5-xCuxZn0.5Fe2O4 (where x = 0.05, 0.15, 0.25, 0.35) nanoparticles obtained from X-ray powder diffractograms. ... 57 Table 4.1 Variation in Raman peak positions in wavenumber (cm^-1) with Mn ion concentration in the spectra of Mn_xZn_1-xFe₂O₄(x =0.00, 0.35, 0.5, 0.65) ferrite nanoparticles.

Square brackets are showing the fractional area of the peak. ... 66 Table 4.2 Variation in Raman peak positions with change in Ni ion concentration (x) and cations (Fe and Zn) distribution in Mn0.5-xNixZn0.5Fe2O4 where x =0.05, 0.15, 0.25, 0.35, 0.45 nanoparticles. The fraction of Zn and Fe cations occupying A site has been estimated from the area of the deconvoluted peaks and is given in the bracket against the peak position. ... 68 Table 4.3 Hyperfine parameters, obtained from fitting of high field ⁵⁷Fe Mössbauer spectrum for Mn_0.5Zn_0.5Fe₂O₄ nanoparticles. I.S -Isomer shift, Q.S- Quadrupole Splitting, H_eff - Hyperfine field, A23-area ratio of second and third lines of the sextet. ... 70 Table 4.4 Fe²⁺ and Fe³⁺ 2p3/2 and 2p1/2 core level and satellite binding energies (in eV) in different iron compounds and spinel ferrites ... 76 Table 4.5 Binding energies ((B. E) in eV) of Fe core levels (2p_3/2 and 2p_1/2) and satellite peaks (Sat.) obtained from the XPS data of different Ni substitution samples. The FWHM is indicated in the bracket against each binding energy. ... 78

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Table 4.6 Binding energies (in (eV)) of Zn 2p, Mn 2p, and Ni 2p core levels along with a satellite peak (Sat.) obtained from the XPS data of different Ni substitution samples. The estimated FWHM is indicated in the bracket against each binding energy. ... 79 Table 4.7 Cations distribution in tetrahedral (A) and octahedral (B) sites in Mn0.5- xNixZn0.5Fe2O4 nanoparticles (x = 0.05, 0.15, 0.25 and 0.35) as estimated from the XPS studies. ... 80 Table 4.8 Observed and calculated intensity ratio of X-ray diffraction peaks from Mn_0.5-

xNi_xZn_0.5Fe₂O₄ where x = 0.05, 0.15, 0.25, 0.35, 0.45 nanoparticles ... 81 Table 4.9 Cations distribution in tetrahedral (A) and octahedral (B) sites in spinel structure of Mn0.5-xNixZn0.5Fe2O4 where x = 0.05, 0.15, 0.25, 0.35, 0.45 nano-particles estimated finally XRD studies. ... 82 Table 4.10 Cations distribution in tetrahedral (A) and octahedral (B) sites in spinel structure of Mn_0.5-xNi_xZn_0.5Fe₂O₄ where x = 0.05, 0.15, 0.25, 0.35, 0.45 nano-particles estimated from the Raman, Mössbauer, XPS and finally XRD studies. ... 83 Table 4.11 Lattice parameter (aexp, ath) and oxygen parameter (u) of Mn0.5-xNixZn0.5Fe2O4

where x = 0.05, 0.15, 0.25, 0.35, 0.45 nanoparticles. ... 85 Table 4.12 Variation in Raman peak positions with change in Cu ion concentration (x) and cations (Mn, Fe and Zn) distribution in Mn_0.5-xCu_xZn_0.5Fe₂O₄where x= 0.05, 0.15, 0.25 and 0.35 nanoparticles. The fraction of Mn, Zn and Fe ions occupying A site was estimated from the area of the deconvoluted peaks and is given in the bracket against the peak position. ... 88 Table 4.13 Hyperfine parameters, obtained from fitting of high field ⁵⁷Fe Mössbauer spectrum for Mn_0.5Zn_0.5Fe₂O₄ nanoparticles. I.S –Isomer shift, Q.S- Quadrupole Splitting, H_eff -Hyperfine field, A₂₃-area ratio of second and third lines of the sextet... 89 Table 4.14 Binding energies (in eV) of Fe core levels (2p3/2 and 2p1/2) and a satellite (Sat.) peak as obtained from the XPS data of different Cu substitution samples. The peak width (FWHM) is indicated in the bracket against each binding energy. A and B represents A-site and B-site respectively. ... 91 Table 4.15 Binding energies (in eV) of Mn 2p, Zn 2p, O1s and Cu 2p core levels along with a satellite peak (Sat.) as obtained from the XPS data of different Cu substituted samples. The estimated FWHM is indicated in the bracket against each binding energy. A or B represents the sites occupied by the cation. ... 92 Table 4.16 Cations distribution in tetrahedral (A) and octahedral (B) sites in Mn0.5- xCu_xZn_0.5Fe₂O₄ nano-particles (x = 0.05, 0.15, 0.25 and 0.35) as estimated from the XPS studies. ... 93

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Table 4.17 Calculated and observed intensity ratio of diffraction peaks in X-ray diffractograms from Mn_0.5-xCu_xZn_0.5Fe₂O₄ where x = 0.05, 0.15, 0.25 and 0.35 nanoparticles.

Calculated structure factors for various Bragg planes comprising of different ions are also included. ... 94 Table 4.18 Cations distribution in tetrahedral (A) and octahedral (B) sites in spinel structure of Mn0.5-xCuxZn0.5Fe2O4 where x = 0.05, 0.15, 0.25 and 0.35 nano-particles as estimated from the calculated and observed XRD intensity ratios for two pairs of planes. Calculated values of magnetic moments too are included. ... 94 Table 4.19 Cations distribution in tetrahedral (A) and octahedral (B) sites in spinel structure of Mn0.5-xCuxZn0.5Fe2O4 where x = 0.05, 0.15, 0.25, 0.35nano-particles estimated from the Raman, Mössbauer, XPS and finally XRD studies. ... 95 Table 4.20 The structural data of Mn_0.5-xCu_xZn_0.5Fe₂O₄ (where x = 0.05, 0.15, 0.25, 0.35) nanoparticles. ... 97 Table 5.1 Effect of Mn concentration in MnxZn1-xFe2O4 nanoparticles on their magnetization (M), blocking temperature (TB) and magneto crystalline anisotropy (Keff). ... 106 Table 5.2 Magnetization (M in emu/g), coercivity (Hc in Oe), particle size (D in nm), magneto crystalline anisotropy (K_effin erg. cm^-3) and blocking temperature (T_B in K) of Mn_0.5-

xNi_xZn_0.5Fe₂O₄ (x =0.05, 0.15, 0.25, 0.35, 0.45) ferrite nanoparticles. Calculated values of magnetic moments are also included in the table. ... 109 Table 5.3 Hyperfine parameters estimated from the room temperature Mössbauer spectra of pristine and Ni substituted Mn-Zn ferrite nanoparticles ... 110 Table 5.4 Hyperfine parameters obtained from the room temperature Mössbauer spectra of pristine and Cu substituted Mn-Zn ferrite nanoparticles ... 116 Table 5.5 Magnetization (M), blocking temperature (TB) obtained from experimental methods. Calculated values of magnetic moments from cation distribution are also included.

... 117 Table 6.1 Effect of Mn concentration in MnxZn1-xFe2O4 nanoparticles on their magnetization (M) blocking temperature (TB) and FMR parameters i.e. line width (∆Hpp), resonance field (Hr), g-value, gyromagnetic ratio (γ) and spin-spin relaxation time (T2)... 122 Table 6.2 Effect of Ni concentration in Mn0.5-xNixZn0.5Fe2O4 (x = 0.05, 0.15, 0.25, 0.35, 0.45) nanoparticles on their magnetization (M) at 4 T, blocking temperature (TB) and FMR parameters i.e. line width (∆Hpp), resonance field (Hr), g-value, gyro magnetic ratio (γ), spin- spin relaxation time (T₂). ... 123

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Table 6.3 Magnetization (M), blocking temperature (T_B), line-width (∆H_pp), resonance field (H_r), Lande’s g factor, gyromagnetic ratio (γ) and spin-spin relaxation time (T₂) of Mn_0.5-

xCuxZn0.5Fe2O4 nanoparticles where x = 0.05, 0.15, 0.25 and 0.35. ... 126