Raman spectroscopy

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Table of contents

Abstract
Résumé
Riassunto
1 Introduction
1.1 Generalities about magnetoelectric multiferroics
1.2 Magnetically induced ferroelectricity
1.2.1 Classification of multiferroics
1.2.2 Phenomenological theory
1.2.3 Microscopic theories
1.3 (AMn3)Mn4O12 quadruple perovskites
1.3.1 Open questions and strategy for the Thesis
2 Experimental methods
2.1 High-pressure/high-temperature syntheses
2.2 Diffraction techniques
2.3 Thermodynamics measurements
2.3.1 Transport properties
2.3.2 Magnetization
2.3.3 Heat capacity
2.4 Spectroscopy techniques
2.4.1 Difference between Infrared and Raman spectroscopy
2.4.2 Sample preparation for spectroscopy
2.4.3 Fourier Transform InfraRed (FTIR) Spectrometer
2.4.4 Triple-stage Raman spectrometer
2.5 Ferroelectric characterizations
2.5.1 Pyroelectric currents
2.5.2 Dielectric constant
3 Multiferroic properties of (LaMn3)Mn4O12
3.1 Introduction
3.2 Article I: Large ferroelectricity induced by collinear magnetism in the quadruple perovskite (LaMn3)Mn4O12
Fig. 3.1 Cell-parameters vs temperature
Fig. 3.2 Pyrocurrents vs Temperature
Fig. 3.3 Remnant polarization vs T
Fig. 3.4 Magnetoelectric coupling measurements
4 Raman and IR spectroscopy study of the spin-lattice coupling in (LaMn3)Mn4O12
4.1 Introduction
4.2 Article II: Evidence of strong magnetoelastic coupling driving magnetic ferroelectricity
Fig 4.1 Infrared spectra
Fig 4.2 Raman spectrum
Fig 4.3 Infrared frequencies vs temperature
Fig 4.4 Raman frequencies vs temperature
Fig 4.5 Dielectric constant vs frequency
Fig 4.6 Specific heat vs magnetic field
5 Effect of the chemical pressure (La3+/Y3+ substitution)
5.1 Introduction
5.2 Article III: Effect of chemical pressure induced by the La3+/Y3+ substitution on the magnetic ordering of (AMn3)Mn4O12 quadruple perovskites
5.3 Supplementary information on article III
6 Multiferroic properties of the new quadruple perovskite (YMn3)
6.1 Motivations
6.2 Article IV: Evidence of centrosymmetry breaking in the magnetic ferroelectric (YMn3)Mn4O12
Fig. 6.1 Pyroelectric currents vs temperature
Fig. 6.2 Remnant polarization vs temperature
Fig. 6.3 Remnant polarization vs poling electric field
Fig. 6.4 Capacitance vs temperature
Fig. 6.5 Electrical resistivity vs temperature
Fig. 6.6 Single-crystal diffraction patterns
Fig. 6.7 Scheme of the super-cell
Conclusions and perspectives
Bibliography