Design of Single‐Molecule Multiferroics for Efficient Ultrahigh‐Density Nonvolatile Memories

Abstract

It is known that an isolated single‐molecule magnet tends to become super‐paramagnetic even at an ultralow temperature of a few Kelvin due to the low spin switching barrier. Herein, single‐molecule ferroelectrics/multiferroics is proposed, as the ultimate size limit of memory, such that every molecule can store 1 bit data. The primary strategy is to identify polar molecules that possess bistable states, moderate switching barriers, and polarizations fixed along the vertical direction for high‐density perpendicular recording. First‐principles computation shows that several selected magnetic metal porphyrin molecules possess buckled structures with switchable vertical polarizations that are robust at ambient conditions. When intercalated within a bilayer of 2D materials such as bilayer MoS2 or CrI3, the magnetization can alter the spin distribution or can be even switched by 180° upon ferroelectric switching, rendering efficient electric writing and magnetic reading. It is found that the upper limit of areal storage density can be enhanced by four orders of magnitude, from the previous super‐paramagnetic limit of ≈40 to ≈106 GB in.−2, on the basis of the design of cross‐point multiferroic tunneling junction array and multiferroic hard drive.

Electric-field-assisted non-volatile magnetic switching in a magnetoelectronic hybrid structure

“…After removing the E- and H-fields, the FL magnetization rotates 180° and stabilizes in the antiparallel state because of the magnetic shape anisotropy as shown in Figure 9 H. Hence, the E-field-induced magnetoelastic anisotropy dominates over the magnetic shape anisotropy (see details in Figure S15 in the supplemental information ) and helps the magnetization overcome the energy barrier to facilitate the 180° reversal of the FL ( Hu et al., 2011 ). Both the aforementioned experimental and simulation results firmly elucidate that the angle-dependent magnetic switching, the TMR modulation and non-volatile and reversible 180° magnetization switching by the E-fields should result from competition among the E-field-induced magnetoelastic anisotropy, the magnetic shape anisotropy, and the unidirectional anisotropy introduced from the external small H-field in the hybrid, facilitating energy-efficient spintronic devices ( Yang et al., 2019 ). The simulated moments of the RL are hardly influenced by due to the strong exchange bias field, which is consistent with the experimental results in Sec.…”

“…Therefore, a minimum magnetic field (switching field) is a prerequisite to realize a 180° magnetic switching. Such a large reduction in switching field is highly beneficial to energy-efficient spintronic devices ( Liu, et al., 2011 ; Yang, et al., 2019 ). The magnetic switching can be achieved by the E-field (∼6 kV/cm) with a relatively small H-field (∼12 Oe) bias, as illustrated in Figure 3 F. Such a tunability can be comparable with that (−75% with a 400 V gate voltage) in the PMN-PT (011)/Ta/Ru/IrMn/CoFe/Ru/CoFeB/MgO/CoFeB/Ta/Ru hybrid device with a lateral electric field configuration ( Zhang et al, 2020 ).…”

“…Therefore, a minimum magnetic field (switching field) is a prerequisite to realize a 180 ll OPEN ACCESS iScience 24, 102734, July 23, 2021 iScience Article magnetic switching. Such a large reduction in switching field is highly beneficial to energy-efficient spintronic devices (Liu, et al, 2011;Yang, et al, 2019). The magnetic switching can be achieved by the E-field ($6 kV/cm) with a relatively small H-field ($12 Oe) bias, as illustrated in Figure 3F.…”

Two dimensional ferroelectrics: Candidate for controllable physical and chemical applications

“…For example, in multiferroic MXene, VS 2 , MoN 2 bilayers 76 and ultrathin CuCrS 2 or CuCrSe 2 , 77 it was found that the magnetizations can be reversed by the FE switching owing to strong magnetoelectric coupling. Furthermore, when metal porphyrin (MP) molecule is intercalated in 2D materials like bilayer MoS 2 or FM CrI 3 , the magnetization, spin distribution or direction of single MP molecules can be switched upon FE reversal 46 …”

Switching metal complexesviaintramolecular electron transfer: connections with solvatochromism

“…The ability to reversibly switch between two or more states, aside from being fascinating from a fundamental chemistry perspective, is an important feature for practical applications in sensing, displays, molecular electronics, and in particular, data storage. [1][2][3][4] While the miniaturization of silicon-based components faces major obstaclessuperparamagnetism, quantum effects, and heat, for example [4][5][6] switchable molecules offer the potential to store data at the molecular scale, or serve as individual electronic or spintronic components in a device. Meanwhile, the vivid color changes that often accompany the transition between states lend these systems the potential for use as molecular scale components in chromic-based sensors and displays.…”