Reversible electrical switching of spin polarization in multiferroic tunnel junctions

Abstract

Spin-polarized transport in ferromagnetic tunnel junctions, characterized by tunnel magnetoresistance, has already been proven to have great potential for application in the field of spintronics and in magnetic random access memories. Until recently, in such a junction the insulating barrier played only a passive role, namely to facilitate electron tunnelling between the ferromagnetic electrodes. However, new possibilities emerged when ferroelectric materials were used for the insulating barrier, as these possess a permanent dielectric polarization switchable between two stable states. Adding to the two different magnetization alignments of the electrode, four non-volatile states are therefore possible in such multiferroic tunnel junctions. Here, we show that owing to the coupling between magnetization and ferroelectric polarization at the interface between the electrode and barrier of a multiferroic tunnel junction, the spin polarization of the tunnelling electrons can be reversibly and remanently inverted by switching the ferroelectric polarization of the barrier. Selecting the spin direction of the tunnelling electrons by short electric pulses in the nanosecond range rather than by an applied magnetic field enables new possibilities for spin control in spintronic devices.

Ferroelectric control of spin-transfer torque in multiferroic tunnel junctions

“…The TER associated with ferroelectric polarization switching has been observed experimentally in BaTiO 3 -and PbTiO 3 -based FTJs in which either La 2/3 Sr 1/3 MnO 3 or SrRuO 3 is used as one of the electrodes while the other side of the ferroelectric thin film is in contact with the tip of an atomic force microscope [24][25][26] . The predicted simultaneous TMR and TER effects 23 have also been demonstrated experimentally in La 2/3 Sr 1/3 MnO 3 /BaTiO 3 /Fe (or Co) MFTJs [27][28][29][30][31][32][33][34] . Although the majority of the work deals with low bias, the existence of TER at finite bias has been predicted based on calculations using a semiclassical approximation 19 and first-principles 35 in FTJs, and model tight-binding calculations in MFTJs 36 .…”

Electric-field switching of perpendicularly magnetized multilayers

“…Various studies have been published on electric-field-controlled magnetic effects in recent years, including magnetic domain wall propagation, 1-8 magnetic phase transitions, [9][10][11][12] spin polarization, 13,14 magnetic anisotropy [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and exchange bias. [33][34][35][36][37] Electric-field control of perpendicular magnetic anisotropy (PMA) would open up new prospects for the realization of high-density magnetic memory and logic technologies operating at low energy consumption levels.…”

Giant electrode effect on tunnelling electroresistance in ferroelectric tunnel junctions

“…Moreover, the functioning of solid-state memories based on FTJs has been demonstrated 3,32 and the memristive behaviour with resistance variations exceeding two orders of magnitude was observed for FTJs with the BaTiO 3 (BTO) barrier 32,33 . At the same time, multiferroic tunnel junctions, combining ferromagnetic electrodes with a ferroelectric barrier, were found to display four resistance states 21,24 and the ability to electrically switch the spin polarization 34 . These properties are promising for high-density memory and spintronic applications of such junctions.…”