ELECTRICAL, DIELECTRIC AND MAGNETOCALORIC PROPERTIES OF SELECTED A- and B-SITE SUBSTITUTED MANGANITES SUJIT KUMAR BARIK NATIONAL UNIVERSITY OF SINGAPORE 2011 ELECTRICAL, DIELECTRIC AND MAGNETOCALORIC PROPERTIES OF SELECTED A- and B-SITE SUBSTITUTED MANGANITES SUJIT KUMAR BARIK (M. Tech., Indian Institute of Technology, Kharagpur, India) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN SCIENCE DEPARTMENT OF PHYSICS NATIONAL UNIVERSITY OF SINGAPORE 2011 Dedicated To My Beloved Family ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS It is a great privilege to express my deep sense of gratitude to my supervisor Asst. Prof. R. Mahendiran for his extensive guidance, valuable suggestions, thought provoking ideas, continuous encouragement and support in last five years. I also learned to overcome frustration, unshaken by failure from him, which will help me in different ways of my research carrier. I am also highly grateful to my co-supervisor Dr. S. N. Piramanagayam for encouraging and inspiring me in all these years. I would like to express my sincere thank to Prof. B.V.R Chowdari for allowing me to use his laboratory for sample preparation. I am thankful to Dr. M. V. V. Reddy for helping me to analyze the XRD data by Reitveld refinement. My heartly thank to my colleages, Mr. V. Suresh Kumar, Mr. Vinayak B. Naik, Mrs. Aparnadevi, Dr. C. Krishnamoorti, Mr. Mark, Mr. Alwyn Rebello, Dr. Rucha Desai, Dr. Raj sankar, Mr. Tan choon, Mr. Zhu bin and Mr. Mahesh Repaka for useful discussions during the years. The financial supports from Research scholarship, NUSNNI (National University of Singapore Nanoscience and Nanotechnology Initiative) and Dr. R. Mahendiran are greatly acknowledged. I would also like to thank the academic and administrative staffs of the Department of Physics, NUS for their help in last five years. A word of thank to earlier flatmates and my friends, Mr. Vishal Sharma, Dr. Yogesh Kumar Sharma, Dr. Raju Gupta and Mr. Mohan Singh Dhoni for keeping fruitful and enjoyable environment at home during my stay with them. I also thank to my close friends in NUS comprising Mr. V. Suresh Kumar, Mr. V. B. Naik, Mr. Bibin Thomas Anto, Mr. Venkatesh and Mr. Saran Kumar to make the days enjoyable. I am also thankful to Mr. Prasanta Sahani, Mr. Sashi Bhusan Rout, Mr. Satyananda Kar, Mr. Satyananda Barik, Mr. Rajeeb kumar Jena, Mr. Narahari Mahanta, Mr. Bijay Kumar Das, Mr. Satyanarayan Bhuyan, Mr. Manish Singh and other friends for their help and support. I place my deep sense of indebtedness to my Father (Mr. Jitendra Kumar Barik), Mother (Mrs. Janaki Barik), Grandmother (Late Pagili Barik), Father-in-law (Dr. Dasarathi Behera), Mother- in-law (Mrs Golap Manjari Behera), Brothers (Dr. Subrat Kumar Barik and Mr. Ratikanta Barik), Sisters (Mrs. Saroj Bala Barik, Mrs. i ACKNOWLEDGEMENTS Bandana Mahakud and Mrs. Sujata Biswal), Brother-in-laws (Mr. Dibakar Barik, Mr. Manoranjan Mahakud, Dr. Ramesh Biswal and Mr. Kharabela Behera), sister in laws (Mrs. Tanaya Barik and Mrs. Rebati Barik) and nephews (Sonu, Sanjib, Guddu, Tutu, Prachi, Payal), who have inspired, encouraged and supported me to reach this stage. Without their support, I could have not reached this stage. I specially thank to my wife (Mrs Lopamudra Barik) and my loving daughter (Ms Vaishnavi Barik) for their moral support and constant source of encouragement during my research work. At last but not least, I thank to all my well wishers, my friends and my relatives (whose names are not mentioned) for their unconditional help and support. ii TABLE OF CONTENTS TABLE OF CONTENTS  ACKNOWLEDGEMENTS---------------------------------------------------------------i  TABLE OF CONTENTS----------------------------------------------------------------iii  SUMMARY--------------------------------------------------------------------------------vii  LIST OF PUBLICATIONS--------------------------------------------------------------x  LIST OF TABLES-----------------------------------------------------------------------xii  LIST OF FIGURES---------------------------------------------------------------------xiii  LIST OF SYMBOLS-------------------------------------------------------------------xxii 1. Introduction 1.1 Manganites-------------------------------------------------------------------------------2 1.1.1 Crystallographic structure -----------------------------------------------------2 1.1.2 Average ionic radii at the A-site ---------------------------------------------4 1.1.3 Size Variance (  A2 ) at the A-site----------------------------------------------4 1.2 Important physical properties in manganite-----------------------------------------6 1.2.1 Orbital Ordering ----------------------------------------------------------------6 1.2.2 Electronic features in hole doped manganites------------------------------9 1.2.3 Magnetoresistance in hole doped manganite (La1-xSrxMnO3)-----------10 1.2.4 Charge Ordering --------------------------------------------------------------13 1.2.5 Phase separation---------------------------------------------------------------16 1.3 Magnetoimpedance--------------------------------------------------------------------18 1.3.1 Introduction--------------------------------------------------------------------18 1.3.2 Phenomenology of GMI------------------------------------------------------20 1.4 Dielectric properties-------------------------------------------------------------------29 1.5 Magnetocaloric properties------------------------------------------------------------36 1.6 Scope and Objective of the present work-------------------------------------------40 1.7 Organization of the thesis-------------------------------------------------------------40 2. Experimental Techniques iii TABLE OF CONTENTS 2.1 Introduction-----------------------------------------------------------------------------42 2.2 Synthesis of materials-----------------------------------------------------------------42 2.3 Sample Characterization Techniques-----------------------------------------------43 2.3.1 X-Ray Diffraction-------------------------------------------------------------43 2.3.2 Dc magnetization measurements-------------------------------------------44 2.3.3 Calorimetric measurements-------------------------------------------------46 2.3.4 Dc magnetotransport measurements----------------------------------------47 2.3.5 Magnetoimpedance measurements-----------------------------------------47 2.3.6 Dielectric measurements-----------------------------------------------------50 3. Electrical, dielectric and magnetocaloric properties of La0.7-xBixSr0.3MnO3 3.1 Introduction-----------------------------------------------------------------------------52 3.2 Experimental Details------------------------------------------------------------------56 3.3 Results and Discussions---------------------------------------------------------------57 3.3.1 Structural Characterization---------------------------------------------------57 3.3.2 DC magnetic properties and Phase diagram-------------------------------59 3.3.3 Dc electrical and magnetotransport properties---------------------------69 3.3.4 Calorimetric properties ------------------------------------------------------75 3.3.5 Discussions of dc electrical and magnetic properties--------------------77 3.3.6 Magnetocaloric Properties of x ≤ 0.4---------------------------------------81 3.3.7 AC Magnetoimpedance properties of x = 0.1 and 0.2--------------------90 3.3.7.1 Results--------------------------------------------------------------------92 3.3.7.2 Discussions--------------------------------------------------------------99 3.3.8 Dielectric properties of x ≥ 0.3 --------------------------------------------102 3.3.8.1 Results-------------------------------------------------------------------102 3.3.8.2 Discussions-------------------------------------------------------------109 3.4 Conclusions---------------------------------------------------------------------------115 4. Electrical, dielectric and magnetocaloric properties of La0.7Sr0.3Mn1-xFexO3 4.1 Introduction---------------------------------------------------------------------------118 4.2 Experimental Details-----------------------------------------------------------------120 4.3 Results and Discussions-------------------------------------------------------------121 iv TABLE OF CONTENTS 4.3.1 Structural Characterization-------------------------------------------------121 4.3.2 Dc magnetic properties-----------------------------------------------------123 4.3.3 Dc electrical resistivity and magnetotransport properties--------------127 4.3.4 Magnetocaloric properties of x ≤ 0.2--------------------------------------129 4.3.5 Magnetoimpedance properties of x ≤ 0.15-------------------------------130 4.3.6 Dielectric properties of x ≥ 0.3---------------------------------------------155 4.3.6.1 Results-------------------------------------------------------------------155 4.3.6.2 Discussions-------------------------------------------------------------161 4.4 Conclusions---------------------------------------------------------------------------165 5. Electrical and magnetocaloric properties of La0.5Ca0.5Mn1-xNixO3 (x ≤ 0.08) 5.1 Introduction---------------------------------------------------------------------------167 5.2 Experimental Details ----------------------------------------------------------------168 5.3 Results and Discussions-------------------------------------------------------------168 5.3.1 Structural Characterization ------------------------------------------------168 5.3.2 Dc electrical, magnetic and magnetotransport properties--------------170 5.3.3 Magnetocaloric properties--------------------------------------------------175 5.3.4 Magnetoimpedance properties of x = 0.04-------------------------------181 5.4 Conclusions---------------------------------------------------------------------------188 6. Conclusions and Future work 6.1 Conclusions---------------------------------------------------------------------------190 6.1.1. Bi doping at the A-site in La0.7-xBixSr0.3MnO3--------------------------190 6.1.1.1. Crystal structure, dc electrical and magnetic properties---------190 6.1.1.2. Magnetocaloric properties-------------------------------------------191 6.1.1.3. Magnetoimpedance properties--------------------------------------192 6.1.1.4. Dielectric properties--------------------------------------------------193 6.1.2. Fe doping at the B-site in La0.7Sr0.3Mn1-xFexO3-------------------------194 6.1.2.1. Dc electrical, magnetic and magnetocaloric properties----------194 6.1.2.2. Magnetoimpedance properties--------------------------------------195 v TABLE OF CONTENTS 6.1.2.3. Dielectric properties--------------------------------------------------195 6.1.3. Ni doping at the B-site in La0.5Ca0.5Mn1-xNixO3------------------------196 6.1.3.1. Dc electrical, magnetic and magnetocaloric properties----------196 6.1.3.2. Magnetoimpedance properties of x = 0.04-------------------------196 6. Future works--------------------------------------------------------------------------197 Bibliography----------------------------------------------------------------------------------199 vi SUMMARY SUMMARY Mn-based perovskite oxides (manganites) have been studied extensively for the past fifteen years due to the colossal dc magnetoresistance behavior exhibited by them and their strong correlation between charge, spin and lattice degrees of freedom. In this thesis, I have investigated electrical, magnetotransport (dc and ac), dielectric and magnetocaloric properties in selected A- and B-site substituted manganites having the general formula ABO3, where A=RE1-xAEx (RE=La3+, Pr3+, Nd3+and AE=Sr2+, Ca2+) and B = Mn. The investigated systems are: La0.7-xBixSr0.3MnO3 (A-site doped), La0.7Sr0.3Mn1-xFexO3 (B-site doped) and La0.5Ca0.5Mn1-xNixO3 (B-site doped). La0.7-xBixSr0.3MnO3 (A-site doped): The Bi doping in La0.7Sr0.3MnO3 transforms the low temperature ground state from a ferromagnet metal (x = 0) to a charge-ordered antiferromagnetic insulator for x ≥ 0.35. While the paramagnetic-ferromagnetic transition is second-order in x ≤ 0.25, it changes into first-order for x = 0.3, which is at the bicritical point. Magnetic phase diagram has been obtained. The compound x = 0.3 shows unusual electrical, magnetic and magnetotransport properties, which includes hysteresis in magnetization as a function of temperature, field-induced metamagnetic transition in the paramagnetic state, field-induced insulator to metal transition at low temperature, cluster glass state below 100 K, CMR state below 100 K, and enormously large residual resistivity (~ 104) at 20 K. 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Mahendiran, ―Magnetic and < /b> calorimetric studies of < /b> magnetocaloric < /b> effect in La0.7th xPrxCa0.3MnO3‖ oral presentation at 56 Annual Conference on Magnetism & Magnetic Materials, USA (Nov 2011)  S K Barik and < /b> R Mahendiran, ―Large ac magnetoresistance and < /b> magnetoreactance of < /b> La0.6Bi0.1Sr0.3MnO3 in low dc bias magnetic field (H ≤ 1 kOe)‖, oral presentation at IEEE International Magnetics Conference, Taipei,... USA (2010)  S K Barik, and < /b> R Mahendiran, ―Effect of < /b> Bi doping on magnetoresistance in La0.7-xBixSr0.3MnO3‖, oral presentation at ICMAT, Singapore (June 2009)  S K Barik, and < /b> R Mahendiran, ―Giant magnetoimpedance and < /b> magnetocaloric < /b> studies in La0.7Sr0.3Mn1-xFexO3‖, poster presentation at Asianano Conference, Biopolis, Singapore (2008)  L M C Mark, S K Barik, and < /b> R Mahendiran, ―Magnetically modulated... and < /b> R Mahendiran, ―Normal and < /b> Inverse magnetocaloric < /b> effects in La0.5Ca0.5Mn1-xNixO3‖, Solid State Commun 150, 1670 (2010) x LIST OF < /b> PUBLICATIONS  A < /b> Rebello, V B Naik, S K Barik, M C Lam and < /b> R Mahendiran, ―Giant ac electrical response of < /b> La0.7Sr0.3MnO3 in sub-kilogauss magnetic fields‖, Mater Res Soc Symp Proc 1256, N04 (2010)  S.K.Barik, A < /b> Rebello, C L Tan, and < /b> R Mahendiran, ―Giant magnetoimpedance... Taipei, Taiwan (April 2011)  S K Barik and < /b> R Mahendiran, ―Anomalous ac magnetoresistance in La0.5Ca0.5Mn1-xNixO3 (x = 0, 0.04)‖, poster presentation at 55th Annual Conference on Magnetism & Magnetic Materials, USA (Nov 2010)  A < /b> Rebello, V B Naik, S K Barik, L M C Mark, and < /b> R Mahendiran, ―Giant ac electrical response of < /b> La0.7Sr0.3MnO3 in sub- kilogauss magnetic fields‖, oral presentation at MRS Spring... Submitted to Solid State Communication  S K Barik and < /b> R Mahendiran, ―Huge low-field ac magnetoresistance in La0.7Sr0.3Mn0.95Fe0.05O3 realized by the ac impedance method‖, Submitted to Solid State Science (1.5 years ago)  S K Barik and < /b> R Mahendiran, ―Impact of < /b> Fe doping on radiofrequency magnetotransport in La0.7Sr0.3Mn1-xFexO3‖ J Appl Phys (Accepted)  S K Barik, M Aparnadevi, A < /b> Rebello, V B Naik and.< /b> .. R Mahendiran and < /b> B Raveau, ―Magnetic and < /b> calorimetric investigation of < /b> magnetocaloric < /b> effect in Pr0.46Sr0.54MnO3‖, Appl Phys Lett 98, 112506 (2011)  S.K Barik, and < /b> R Mahendiran, ―Effect of < /b> Bi doping on magnetoresistance in La0.7-xBixSr0.3MnO3‖J Nanoscience and < /b> Nanotechnology, 11, 2603 (2011)  S K Barik, C Krishnamoorthi and < /b> R Mahendiran, ―Effect of < /b> Fe substitution on magnetocaloric < /b> effect in La0.7Sr0.3Mn1-xFexO3... Magn and < /b> Magn Mater, 323, 1015 (2011)  C Krishnamoorthi, S K Barik and < /b> R Mahendiran, ―Effect of < /b> Ru-substitution on electrical and < /b> magnetocaloric < /b> properties < /b> of < /b> Nd0.5Ca0.5MnO3‖, Solid State Commun 151, 107 (2011)  S.K Barik, and < /b> R Mahendiran, ―Effect of < /b> Bi doping on magnetic and < /b> magnetocaloric < /b> properties < /b> of < /b> La0.7-xBixSr0.3MnO3 (0 ≤ x ≤ 0.4)‖ J Appl Phys 107, 093906 (2010)  C Krishnamoorthi, S K Barik,... properties < /b> and < /b> to understand the fundamental physics involved This chapter is organized as follows First, we present a < /b> brief overview on perovskite manganese based oxides (manganites) and < /b> its colossal magnetoresistance effect Then we discuss some intriguing features such as charge-orbital ordering, phase separation and < /b> related features in manganites Later, we present a < /b> brief description about the ac... Chapter 1 Introduction This chapter ends with a < /b> brief summary on the organization of < /b> the rest of < /b> the chapters in the thesis 1.1 Manganites 1.1.1 Crystallographic structure Manganese based oxides (manganites) generally belong to perovskite structure with the general formula ABO3, where A< /b> site is occupied by bigger size cations such as rare earth or alkaline earth ions and < /b> B site is occupied by smaller... expressed as, t  rA  rO 2  rB  rO  , (1.1) 2 Chapter 1 Introduction where rA , rB and < /b> rO are the average ionic radii of < /b> A-< /b> site, B- site and < /b> oxygen anion respectively [2,3] (a)< /b> (b) Fig.1.1: Schematic diagram of < /b> the (a)< /b> Cubic perovskite structure, and < /b> (b) MnO6 octahedra When t = 1, the structure belongs to cubic The orthorhombic and < /b> rhombohedral structures are commonly observed in manganites in which . I am also thankful to Mr. Prasanta Sahani, Mr. Sashi Bhusan Rout, Mr. Satyananda Kar, Mr. Satyananda Barik, Mr. Rajeeb kumar Jena, Mr. Narahari Mahanta, Mr. Bijay Kumar Das, Mr. Satyanarayan. Mrs. ACKNOWLEDGEMENTS ii Bandana Mahakud and Mrs. Sujata Biswal), Brother-in-laws (Mr. Dibakar Barik, Mr. Manoranjan Mahakud, Dr. Ramesh Biswal and Mr. Kharabela Behera), sister in laws (Mrs (Late Pagili Barik), Father-in-law (Dr. Dasarathi Behera), Mother- in-law (Mrs Golap Manjari Behera), Brothers (Dr. Subrat Kumar Barik and Mr. Ratikanta Barik), Sisters (Mrs. Saroj Bala Barik,