Chapter 12Integration of Multiferroic BiFeO3 Thin Filmsinto Modern Microelectronics 1




12.1. Introduction

Multiferroic materials, which simultaneously display ferroelectric and magnetic ordering, have recently attracted a great deal of attention because of the intriguing science behind their magnetoelectric (ME) coupling phenomenon and their exciting application potential in multiple controlled devices [SPA 05, FIE 05, EER 06, RAM 07, GAJ 07]. By the original definition, such materials that possess two, or all three, of the so-called “ferroic” properties — ferroelectricity, ferromagnetism, and ferroelasticity — in the same phase are known as multiferroics [SPA 05, EER 06], and are depicted in Figure 12.1. However, the current trend is to exclude the requirement for ferroelasticity in practice and to broaden the classification of multiferroics by including antiferroic order such as antiferroelectricity and antiferromagnetism [EER 06]. Generally speaking, multiferroics can be classified into two groups on the basis of the microscopic mechanism that determines their properties [KHO 09]. The first group contains those materials in which ferroelectricity and magnetism have different sources and appear independently of each other, though there is some coupling between them. These materials are often good ferroelectrics with quite large spontaneous polarization (of order of magnitude 10–100 μC/cm2), and their critical temperatures of the magnetic and/or ferroelectric transitions ...

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