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On The Magnetic And Magnetotransport Studies Of Cobaltates And Superconductor/ Ferromagnet Heterostructures

Electronic Theses of Indian Institute of Science

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Title On The Magnetic And Magnetotransport Studies Of Cobaltates And Superconductor/ Ferromagnet Heterostructures
 
Creator Samal, Debakanta
 
Subject Superconductors
Magnetotransport
Cobaltates
Superconductivity
Ferromagnetism
Ferromagnetic Bilayers
Ferromagnetic Trilayers
Thin Films
Magnetoresistance
Magnetism
Spintronics
Magnetoelectronic Materials
Electrodynamics
 
Description The study of the co-existence of singlet superconductivity and ferromagnetism in bulk materials has been a long standing and intriguing problem in condensed matter physics since the superconductivity and ferromagnetism are quantum mechanically antagonistic to each other (i.e. parallel alignment of spins in the ferromagnet and Cooper pairs with oppositely aligned spins in the superconductor).Though it is incompatible to have the coexistence of singlet superconductivity and ferromagnetism in bulk compound, it is highly possible to artificially fabricate superconductor (S)/ferromagnet (F) heterostructures using various thin film deposition techniques and to study the interplay between the two antagonistic quantum phases over their characteristic length scales. The mutual interaction between the two competing order parameters at the interface in hybrid S/F heterostructures give rise to a variety of novel exotic physical phenomena. Moreover, the spin polarized transport and tunneling experiments in S/F heterostructures seem to be very much useful for providing important information on the spin dependent electronic properties of high Tc superconductors below and above the transition temperature. This can help a lot to understand the long debated unusual electronic properties and pairing mechanism of high Tc superconductors. In addition to the rich fundamental aspects buried in the study of S/F heterostructures, one can also use the spin dependent properties of high Tc superconductors in S/F heterostructures to design new spintronics devices from the application point of view.
In this thesis an attempt is made to understand the spin polarized electron transport across S/F heterostructures where the superconductor used is YBa2Cu3O7-δand the ferromagnets are La0.5Sr0.5CoO3, La0.7Sr0.3MnO3, and La0.7Ca0.3MnO3. In addition, the magnetic properties of the La1-x SrxCoO3 system is also investigated in detail.
The thesis is organized in six chapters and a brief summary of each chapter is given below.
Chapter1 gives a brief introduction to the superconductivity, ferromagnetism and the interplay between superconductivity and ferromagnetism at the interface of S/F heterostructures. It also describes various exotic phenomena and the proximity effect that emerges at the S/F interface due to competing interactions. In addition, it also includes a
discussion on various types of indirect magnetic interactions and basic idea about the spin glass ordering in magnetic materials.
Chapter 2 outlines the basic principles of various experimental techniques employed for the work presented in this thesis.
Chapter 3 describes an extensive magnetic and magnetotransport study of the La1-xSrxCoO3 system to understand the manifestation of various magnetic phases associated with it. The first section of this chapter aims at understanding the phase separation scenario in La0.85Sr0.15CoO3. Since the magnetic behavior of La0.85Sr0.15CoO3 is in the border area of spin glass (SG) and ferromagnetic (F) region in the x-T phase diagram; it has been subjected to a controversial debate for the last several years; while some groups show evidence for magnetic phase separation (PS), others show SG behavior. However, the experimental results presented in this thesis clearly demonstrate that the instability towards PS with inhomogeneous states or competing phases in La0.85Sr0.15CoO3 is not inherent or intrinsic to this compound; rather it is a consequence of the heat treatment condition during the preparation method. It is realized that low temperature annealed sample shows PS whereas the high temperature annealed sample shows the characteristics of canonical SG behavior. The second section of this chapter deals with a detailed study about the possible existence of various magnetic phases of La1-xSrxCoO3 in the range 0 ≤x ≤0.5. The dc magnetization study for x ≥0.18 exhibits the characteristic of ferromagnetic like behavior and for x
 
Contributor Anil Kumar, P S
 
Date 2011-06-30T06:41:26Z
2011-06-30T06:41:26Z
2011-06-30
2010-06
 
Type Thesis
 
Identifier http://etd.iisc.ernet.in/handle/2005/1251
http://etd.ncsi.iisc.ernet.in/abstracts/1631/G23843-Abs.pdf
 
Language en_US
 
Relation G23843