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Multiferroic Field Effect Devices

Date : 9/1/2010

SM Wu, SA Cybart, P Yu, MD Rossell, JX Zhang, R Ramesh, RC Dynes
Nature materials 9 (9), 756-761

Electric-field control of magnetization has many potential applications in magnetic memory storage, sensors and spintronics. One approach to obtain this control is through multiferroic materials. Instead of using direct coupling between ferroelectric and ferromagnetic order parameters in a single-phase multiferroic material, which only shows a weak magnetoelectric effect, a unique method using indirect coupling through an intermediate antiferromagnetic order parameter can be used. In this article, we demonstrate electrical control of exchange bias using a field-effect device employing multiferroic (ferroelectric/antiferromagnetic) BiFeO3 as the dielectric and ferromagnetic La0.7Sr0.3MnO3 as the conducting channel; we can reversibly switch between two distinct exchange-bias states by switching the ferroelectric polarization of BiFeO3. This is an important step towards controlling magnetization with electric fields, which may enable a new class of electrically controllable spintronic devices and provide a new basis for producing electrically controllable spin-polarized currents.

Date : 2/4/2013

SM Wu, SA Cybart, D Yi, James M Parker, R Ramesh, RC Dynes
Physical Review Letters 110 (6), 067202

We report the creation of a multiferroic field effect device with a BiFeO3 (BFO) (antiferromagnetic-ferroelectric) gate dielectric and a La0.7Sr0.3MnO3 (LSMO) (ferromagnetic) conducting channel that exhibits direct, bipolar electric control of exchange bias. We show that exchange bias is reversibly switched between two stable states with opposite exchange bias polarities upon ferroelectric poling of the BFO. No field cooling, temperature cycling, or additional applied magnetic or electric field beyond the initial BFO polarization is needed for this bipolar modulation effect. Based on these results and the current understanding of exchange bias, we propose a model to explain the control of exchange bias. In this model the coupled antiferromagnetic-ferroelectric 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 cause bipolar modulation.