Complex oxide heterostructures as multiferroic tunnel junctions

Entirely complex oxide ferromagnetic / ferroelectric / ferromagnetic tunnel junctions were created via Pulsed Laser Deposition (PLD) and patterned into three dimensional tunnel junction structures via photolithography. The system under investigation comprised multiferroic (001) orientated Bismuth Ferrite (BFO) as the tunnel barrier with (001) orientated Lanthanum Strontium Manganate (LSMO) as the magnetic electrodes. The deposited heterostructures were found to be epitaxial, phase pure and atomically smooth, confirmed via X – ray analysis, transmission electron microscopy and atomic force microscope techniques. The magnetic properties of the electrodes (LSMO) were probed by Ferro Magnetic Resonance (FMR) experiments to reveal a thickness dependence to the remnant magnetisation, as well a dependence on the thickness of BFO deposited over the electrode. The tunneling magnetoresistance of the photolithographically patterned junctions was successfully modified via the application of low electric field pulses to the junctions. The experimental results demonstrate a four state memory element, which is attributed to ionic displacements associated with the polarisation reversal in the ferroelectric barrier affecting the complex band structure at ferromagnetic / ferroelectric interfaces, thereby modulating the tunneling magnetoresistance. The experimental results were found to be in agreement with the theoretically predicted magneto electric interface effect and may find applications in novel multi state memory devices