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.
Highlights
With the relentless minimization of integrated circuit size to nanoscale, there are two major issues for the current prevailing is reduced in low-dimensions
The first measured Curie temperature of 2D ferromagnetism (FM) in CrI3 is ≈45 K[17] and ≈10 K in Cr2Ge2Te6.[18] data writing in MRAMs is much more energy-consuming than in FeRAMs, since FE switching
Note that for an isolated single-molecule magnet (N = 0), its magnetism with a spin switching barrier of K (≈meV) cannot survive even at ultralow temperature of a few Kelvin, whereas for a single-molecule FE, K can still be more than hundreds of meV
Summary
With the relentless minimization of integrated circuit size to nanoscale, there are two major issues for the current prevailing is reduced in low-dimensions. Note that for an isolated single-molecule magnet (N = 0), its magnetism with a spin switching barrier of K (≈meV) cannot survive even at ultralow temperature of a few Kelvin, whereas for a single-molecule FE, K can still be more than hundreds of meV For the latter case, even the adjacent dipole– dipole interaction is negligible, the sizable energy barrier would allow FE to survive at ambient conditions. The external stimuli involved in these molecular switches are through inelastic electron injection directly into the molecules from the tip of scanning probe microscopy at the liquid nitrogen temperature This approach is necessary to overcome the large switching barrier (e.g., >2 eV for ClAlPc),[27] but is not so efficient and energysaving for data reading/writing with RAMs. Alternatively, we attempted to build single molecular FE/ multiferroic RAMs that can work at ambient condition. When coupled with 2D materials like bilayer MoS2 or CrI3, the magnetization spin distribution or direction can be switched upon FE switching, thereby offering efficient electric writing + magnetic reading simultaneously
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