Integration of Multiferroic BiFeO $_3$ Thin Films into Heterostructures for Spintronics

The revival of multiferroics is motivated by their exciting physics and their ability to bring novel functionalities to a number of technological fields such as spintronics. The lack of room temperature ferroelectric ferromagnets is a problem and has driven most of the attention thus far to BiFeO$_3$, a ferroelectric weak-ferromagnet with both transition temperatures superior to 300K. In this paper, we report on the properties of BiFeO$_3$ heterostructures and focus on two types of approaches towards BiFeO $_3$-based spintronics devices. One uses BiFeO$_3$ as an exchange bias layer in spin-valve structures in which the magnetic configuration is potentially switchable by an electric field, via the magnetoelectric coupling existing in BiFeO$_3$. The other consists in integrating BiFeO$_3$ ultrathin films as tunnel barriers in magnetic tunnel junctions with the objective of exploiting their ferroelectric character along with their specific symmetry filtering properties. General perspectives for multiferroics in spintronics are given.