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Multiferroic Materials

Multiferroic Materials

Multiferroic materials constitute a class of multifunctional materials presenting in the same time coupled properties in terms of ferromagnetic-ferroelectric and ferroelastic order. On a fundamental scale, the nature of the interactions and in particular the magnetoelastic coupling mechanism is not fully understood despite the amount of experiments. On a technological level, this class of material is interesting in the field of information storage or for microelectromechanical systems development. Among multiferroic materials, BiFeO3 is one is one of the few which presents in the same time both ferroelectric and magnetic order above 300K. However despite this unique property, BiFeO3 also presents a magnetic helicoïdal structure of Fe3+ magnetic moments, this magnetic structure leads to weak magnetoelectric coupling. A drastic increase of magnetoelectric coupling can be obtained through the breakdown of helicoïdal spirale and the formation of an antiferromagnetic linear structure of type G leading to a non-zero mean magnetization.

Multiples ways can be followed to breakdown this helicoidal structure among them:

  1. Reducing the size of the material dimension to a value lower than the cycloid period (~64 nm). This can be obtained by a polyol method for synthetizing BiFeO3 nanoparticles.
  2. Substituting Bi3+ and Fe3+ by Ti4+ and Zr4+ using a ceramic synthesis in order to partially break helicoïdal structure of Fe3+ magnetic moments


MEB picture of BiFeO3 particles obtained with polyol processModification of helicoïdal magnetic order and apparition of ferromagnetic order

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