The Born-Oppenheimer approximation

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Table of contents

1 Literature review 
1.1 Introduction – what is all about
1.1.1 Magnetic refrigeration
1.1.2 Thermodynamic Approach of the Magnetocaloric Effect
1.1.2.1 Thermodynamics of Adiabatic Cooling
1.1.2.2 Magnetocaloric Effect and Adiabatic Demagnetization
1.1.2.3 Entropy and its Dependence on the Magnetic Field
1.1.3 Classification and phenomenology of magnetocaloric materials
1.1.3.1 Magnetic transition order
1.1.3.2 Employment of Maxwell relation
1.1.4 Selection Criteria
1.2 Multiferroic materials
1.2.1 Why multiferroics are interesting ?
1.2.2 Classifying Multiferroics
1.3 Type-I multiferroic : Vanadate RVO3
1.3.1 Multiferroic structure
1.3.2 Magnetic configuration
1.3.2.1 Hund rules
1.3.2.2 Super-exchange interactions
1.3.2.3 Goodenough-Kanamory rules
1.3.3 Phase diagram in rare-earth vanadates
1.3.4 Quantum versus Jahn teller orbitals physics
1.4 Type-II multiferroic: Orthorhombic RMn2O5
1.4.1 General structure
1.4.2 Magnetic moments and exchange interactions
1.4.2.1 Magnetic moment
1.4.3 Exchange interactions
1.4.4 Dzyaloshinskii-Moriya interaction
1.5 Outline of the thesis
2 Experimental and theoretical techniques 
2.1 Sample elaboration and characterization
2.1.1 Sample elaboration
2.1.2 Magnetic characterization
2.2 Ab initio calculations
2.2.1 Introduction to ab initio calculations
2.2.2 Quantum many-body systems
2.2.3 The Born-Oppenheimer approximation
2.2.4 Density functional theory
2.2.4.1 The theorems of Hohenberg and Kohn
2.2.4.2 The Kohn-Sham equations
2.2.4.3 The exchange-correlation functional
2.2.5 Solving the equations
2.2.5.1 The pseudopotentiel basis set
2.2.5.2 The LAPW basis set
2.3 Monte Carlo simulation
2.3.1 Theoretical models
2.3.2 Basic of Monte Carlo simulation
2.3.3 Metropolis algorithm
3 Magnetocaloric effect in oxyde thin films 
3.1 Introduction
3.2 Research progress in rare earth perovskite oxide magnetocaloric materials : From micro to nanoscale
3.2.1 ABO3 perovskites
3.3 PrVO3: An inhomogeneous antiferromagnetic material with random field
3.3.1 Bulk and film magnetic properties
3.4 Strain-induced giant magnetocaloric effect in epitaxial PrVO3 thin films
3.4.1 Outline of the experiments
3.4.2 Magnetic characterization
3.4.2.1 PrVO3 (100nm) deposited on 001-oriented SrTiO3 (STOº substrate
3.4.2.2 PrVO3 (41.7nm) deposited on 001-oriented ¹La, Srº¹Al,TaºO3 (LSAT) substrate
3.4.3 Magnetocaloric properties
3.5 Theoretical calculations
3.5.1 Calculations details
3.5.2 Electronic and structural properties
3.5.3 Magnetic properties
4 Magnetocaloric effect in HoMn2O5 single crystals 
4.1 Introduction
4.2 Why RMn2O5
4.3 Common features
4.3.1 Magnetic structure
4.3.2 Magnetocaloric effect in RMn2O5 at low temperature regime
4.4 Study of HoMn2O5 single crystals
4.4.1 Computational details
4.4.2 Electronic properties
4.4.3 Magnetic properties
4.4.3.1 XMCD at the Ho M4,5edge
4.4.3.2 XMCD at the Mn L2,3 edge
4.4.4 Magnetocaloric properties
4.4.5 Summary
5 General conclusions and future challenges 
Résumé en Francais