YIG/AFE and YIG/FE Heterostructures in Full Thin-Film Form

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Backgrounds and Literature Review

The concept of « ferroic » is referred to the properties of ferroelectricity, ferromagnetism, and ferroelasticity in a crystal, as Aizu concluded in 1970.[41] The most distinct feature of « ferroic » is the existence of domain. The order parameters (dipole moment, magnetic moment, etc.) of atoms or ions in adjacent positions of ferroic materials are arranged in the same direction in the local area due to interaction, thereby forming an ordered region, named « domain ». The domains allow the order parameter of ferroic materials to change with the presence of the external field, and leads to hysteresis loops. Later, it was found that ferrotoroidicity also belongs to the family of « ferroic ». [42] The spontaneous polarized or magnetized domains in ferroic materials allow the order parameter to change with the application of the external fields, and ferroic materials would present hysteresis loops and anomalies at the phase transition.

Ferroelectrics and Antiferroelectrics

The study of ferroelectric materials is generally believed to have begun in 1921, when J. Valasek firstly observed the dielectric anomalies in Rochelle salt. [43] Then, ferroelectric materials develop quickly and become essential components in a broad spectrum of applications. The concept of antiferroelectricity was proposed in 1951 to describe a state where chains of ions in the crystal are spontaneously polarized, but with neighboring chains polarized in antiparallel directions.[44] Since then, various antiferroelectrics have been discovered over the past half century, and research on antiferroelectric materials has received increasing attention.
(1) Ferroelectrics
Ferroelectric materials are a family of materials who display spontaneous polarization in a specific range of temperature, and the polarization of FE materials is reversible with an application of the electric field. In FE materials, the adjacent dipoles in one domain share the same polarization orientation, and orientation of the dipoles can be aligned by an external DC electric field. For illustration, Figure 2.2 (a) shows the electric-field dependence of polarization (P–E) of FEs. When the external electric field turns to the opposite direction, new ferroelectric domains of FEs begin to nucleate and grow up, the domain wall moves, and finally, the polarization reverses. When an electric field is applied to ferroelectric materials, a strain accompanying the polarization reversal process would also be generated in ferroelectrics, as given in Fig. 2.2 (b). The electric-field dependence of strain (S-E) loop in a butterfly shape can be attributed to three effects: the converse piezoelectric effect, the switching, and movements of domain walls.

Solid-State Reaction Process

The raw powders were prepared by the conventional solid-state method according to the chemical formula of the ceramics with 0.5 wt.% excess Pb3O4 to compensate Pb volatilization during sintering. The raw powders were weighed according to the compositions by the balance. Then, they were mixed with deionized water and milling ball according to the weight proportion of 1: (1.4 ~1.8) : (0.7 ~1.0). After 10 hours of ball milling, the mixed powders dried in the oven, sieved with mesh and then calcined at 850 ℃ for 2 hours. After calcination, the calcined powder was milled again for 24 hours and dried overnight before mixing with 6 wt.% of polyethylene glycol as a binder. Next, the calcined powders were uniaxially pressed into pieces of the disc with a thickness around 2 ~3 mm and a diameter of 15 mm. To decompose the binder fully, the green pellets were firstly put at 800 ℃ for 2 hours. Then for sintering, the green pellets were covered in a calcined powder of the same composition in a closed alumina crucible to avoid volatilization of Pb and sintered at 1240 ~1320 °C for 2 to 4 hours. Note that the heating and cooling rate used for both calcination and sintering was 2 °C/min.

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Processing Techniques

The sintered pellets were mechanically ground to a final uniform thickness of approximately 0.5 mm. Then the silver electrodes were coated on two sides of the clean ceramic pellets through the screen printing technique, and the silver sintering was conducted at 700 ~750 °C for 15 ~30 minutes. Finally, the ceramic samples were ready for electrical measurements.

Table of contents :

Table of Contents
List of Tables
List of Figures
1 Introduction
1.1 Motivation
1.2 Scope of Work
2 Backgrounds and Literature Review
2.1 Theoretical Background
2.1.1 Ferroelectrics and Antiferroelectrics
2.1.2 Magnetism and Magnetic Properties
2.1.3 Magnetoelectric materials
2.2 Literature Review
3 Experimental Techniques
3.1 Ceramic Synthesis
3.1.1 Raw materials
3.1.2 Solid-State Reaction Process
3.1.3 Processing Techniques
3.2 Thin Film Preparation
3.2.1 Magnetron Sputtering
3.2.2 Targets Fabrication
3.2.3 Electrodes Deposition
3.3 Characterization Methods
3.3.1 Microstructural Characterization
3.3.2 Electrical Measurements
3.3.3 Magnetic Properties Characterization
3.3.4 Magnetoelectrical Properties Characterization
4 FE and AFE Ceramic Substrates
4.1 PMN-PZT FE Ceramic Substrates
4.1.1 Introduction
4.1.2 Preparation of PMN-PZT Ceramic Substrates
4.1.3 Results and Discussion
4.1.4 Summary
4.2 PLZST AFE Ceramic Substrates
4.2.1 Introduction
4.2.2 Preparation of PLZST Ceramics
4.2.3 Results and Discussion
4.2.4 Summary
4.3 Conclusions
5 CME Coupling Effect in NMG/AFE Heterostructure
5.1 Introduction
5.2 Preparation of NMG/PLZST/NMG
5.2.1 Film Growth
5.2.2 ME Heterostructure Fabrication
5.3 E-field controlled magnetization switching in NMG/PLZST/NMG Heterostructure
5.4 Conclusions
6 CME Coupling Effect of YIG Films on AFE and FE Ceramics
6.1 Preparation of YIG/AFE and YIG/FE Heterostructures
6.1.1 YIG film Growth
6.1.2 Preparation of YIG/Pt/PLZST/Pt and YIG/Pt/PMN-PZT/Pt ME Heterostructures
6.2 YIG/Pt/PLZST/Pt heterostructure
6.2.1 In-plane CME Effect in YIG/Pt/PLZST/Pt Heterostructure
6.2.2 Out-of-plane CME Effect in YIG/Pt/PLZST/Pt Heterostructure
6.2.3 Summary
6.3 YIG/Pt/PMN-PZT/Pt heterostructure
6.3.1 In-plane CME Effect in YIG/Pt/PMN-PZT/Pt heterostructure
6.3.2 Out-of-plane E-field controlled Magnetism in YIG/Pt/PMN-PZT/Pt heterostructure
6.3.3 Summary
6.4 Conclusions: comparison of FE (AFE)/YIG performances
7 CME Coupling Effect of [(TbCo2)/(FeCo)]20 Films on AFE and FE Ceramics
7.1 Preparation of TCFC/AFE and TCFC/FE Heterostructures
7.2 [(TbCo2)/(FeCo)]20/PLZST/Au Heterostructure
7.2.1 CME Effect along Hard Axis
7.2.2 CME Effect along Easy Axis
7.2.3 CME Effect along OOP Direction
7.2.4 Summary
7.3 [(TbCo2)/(FeCo)]20/PMN-PT/Au heterostructure
7.3.1 CME Effect along Hard Axis
7.3.2 CME Effect along Easy Axis
7.3.3 CME Effect along OOP Direction
7.3.4 Summary
7.4 Conclusions
8 YIG/AFE and YIG/FE Heterostructures in Full Thin-Film Form
8.1 Preparation of YIG/AFE and YIG/FE Heterostructures in Full-Thin-Film Form
8.1.1 LNO film Growth
8.1.2 Preparation of Pt/PZ/LNO/SiO2/Si ME Heterostructures
8.1.3 Preparation of Pt/PZT/LNO/SiO2/Si ME Heterostructures
8.1.4 Preparation of YIG/Pt/PZ (PZT)/LNO/SiO2/Si ME Heterostructures
8.2 Results and Discussions
8.2.1 YIG/Pt/PZ/LNO/SiO2/Si Heterostructure
8.2.2 YIG/Pt/PZT/LNO/SiO2/Si Heterostructure
8.3 Conclusions
9 Summary and Future Work
9.1 Summary
9.2 Future Work


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