Electrical Switching of Magnetization in the Artificial Multiferroic CoFeB/BaTiO₃

Abstract

Electronic, magnetic, chemical, and mechanical phenomena occurring in metal/oxide heterostructures have recently received great attention in view of their exploitation in novel solid state devices. In particular, artificial multiferroics, i.e., layered or composite systems made of a ferromagnetic and ferroelectric phase, hold potential for achieving the electric control of the magnetization in spintronic devices. In this paper, a novel artificial multiferroic displaying perpendicular magnetic anisotropy is reported: the CoFeB/BaTiO3 bilayer. At room temperature, the CoFeB magnetic coercive field displays a hysteretic behavior, as a function of the voltage across the BaTiO3 layer, with a 60% variation for complete reversal of the ferroelectric BaTiO3 polarization. This is exploited to achieve the electric switching of the magnetization of individual CoFeB electrodes under a uniform magnetic bias field. Upon the local BaTiO3 polarization reversal, the CoFeB electrode jumps from an initial metastable state into the opposite stable magnetization state, with a characteristic switching time determined by magnetic viscosity. The magnetically assisted bipolar electric switching of the magnetization is demonstrated, via voltage pulses compatible with complementary metal‐oxide semiconductor (CMOS) electronics, under uniform bias fields as low as 10 Oe.

Magneto-ionic effect in CoFeB thin films with in-plane and perpendicular-to-plane magnetic anisotropy

“…As a matter of fact, a reduced M S value was reported for CoFeB/Ta films grown in contact with other oxides. 13 We have estimated the effective anisotropy constant in the virgin state of the samples using the formula…”

“…Noteworthy, in case of CFB-Ta, we were not able to drive the magnetic anisotropy out of the plane by ex-situ annealing, by contrast to what happens, e.g., in Ta/CoFeB/MgO or Ta/CoFeB/BaTiO 3 . 13,22 The difference in magnetic anisotropy between CoFeB grown on top of Pt and Ta may be attributed to the different hybridization at the interface and spin-orbit interaction of the two materials. 25 Other effects, such as strain or asymmetries in interfacial bonding, could also play a role.…”

“…7 Recently, electric field effects on magnetic properties were demonstrated in all-solid-state devices, exploiting mechanisms such as interfacial hybridization induced by a change in electronic d orbital population, magneto-electric coupling in multiferroics and accumulation of charges induced by ferroelectric polarization in artificial multiferroics. [8][9][10][11][12][13] On a parallel line, ion migration has been widely exploited in non-magnetic devices, e.g., made by an oxide layer sandwiched by two metallic layers, suitable for resistive switching technology. 14,15 The magneto-ionic effect, i.e., the electric control of magnetic properties mediated by ion migration, 16,17 is a physical phenomenon connecting these two fields.…”

Cautions to predicate multiferroic by atomic force microscopy

“…To get more detailed information on atomic magnetic moments and local magnetic domains, X-ray magnetic circular dichroism (XMCD) and X-ray magnetic linear dichroism (XMLD) techniques [14][15][16] are usually used individually or combined with photoemission electron microscopy (PEEM) to provide a credible evidence. [17][18][19] Scanning Kerr Microscopy (SKM) based on magneto-optical Kerr effect (MOKE) 20,21 has also been utilized to detect electrically induced changes in local magnetic domains.…”

Impact of semiconducting electrodes on the electroresistance of ferroelectric tunnel junctions

“…The ability of ferroelectric materials to maintain a stable state of polarization in the absence of external electric fields has found applications in many fields, such as nonvolatile memories (FeRAMs), 1 reconfigurable transistors (FeFETs), 2 electric control of magnetism, [3][4][5] and spintronics. 6,7 In recent years, the ability to fabricate ultrathin ferroelectric films has enabled the realization of ferroelectric tunnel junctions (FTJs), with the tunnel barrier made of a few nm-thick ferroelectric film.…”