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Electric Field Control of Exchange Bias in Multiferroic Based Field Effect Devices

Materials Science Seminar
Stephen Wu, University of California, Berkeley
March 27, 2013 11:00AM to 12:00PM
Building 223, Room S105
The electric field control of ferromagnetism has been a long sought after effect, due to the large number of potential applications in electronic/magnetic devices. One possible way to achieve this is by controlling exchange bias, the shift of a magnetic hysteresis curve along the applied field axis due to interface interactions between coupled antiferromagnetic and ferromagnetic materials. By using multiferroic BiFeO3 (BFO), an antiferromagnet (AFM) and ferroelectric (FE) with coupled AFM/FE order parameters, coupled to ferromagnetic (FM) La0.7Sr0.3MnO3 (LSMO), a system can be created where FE order is switched in BFO, which induces a change in AFM order in BFO, which induces a change in exchange bias in LSMO. This system is realized through an electric field effect device with BFO as the dielectric and LSMO as the conducting channel.

These devices are studied through magnetotransport measurements to characterize the magnetic properties of the LSMO channel with respect to BFO FE polarization. Through these measurements it can be shown that, for the first time, exchange bias is being directly controlled through the application of electric field without temperature cycling or any electric or magnetic field cooling/biasing. This effect is reversible and comes concurrently with a change in channel resistance (sometimes over 300%), magnetic coercivity, and magnetic Curie temperature. A model for device behavior is proposed based on these results and the current understanding of exchange bias. Here, coupled AFM/FE order in BFO along with the modulation of interfacial exchange interactions due to ionic displacement of Fe3+ in BFO relative to Mn3+/4+ in LSMO allow for the control of exchange bias in this system.