Multiferroics are materials which exhibit multiple ferroic orderings. The most typical case is ferroelastic and ferroelectric ordering in the same material. Most ferroelectrics also show concurrent or independent ferroelastic ordering. In certain cases, it is hard to assign the primary order parameter. Sometimes ferroelastic and ferroelectric order arise concurrently, in others certain ionic reordering sets in before a polar state is achieved. All ferroelectrics are based on non-centrosymmetric crystal classes.
In the last two decades, the much rarer case of magnetic and ferroelectric ordering in the same material has been addressed. Certain systems display completely independent ordering parameters, others show coupling between magnetic and electric order parameters. In this context, it is technologically highly interesting to know whether room temperature multiferroic states can be achieved in order to form a basis for a magnetoelectric computer memory element.
The presentation will introduce the phenomenology and display a few characteristic cases of the different crystals known. Then it will be outlined, how nuclear solid state techniques can help to improve the understanding of these materials.