Toward Nonvolatile Spin–Orbit Devices: Deposition of Ferroelectric Hafnia on Monolayer Graphene/Co/HM Stacks

Abstract

While technologically challenging, the integration of ferroelectric thin films with graphene spintronics potentially allows the realization of highly efficient, electrically tunable, nonvolatile memories through control of the interfacial spin−orbit driven interaction occurring at graphene/Co interfaces deposited on heavy metal supports. Here, the integration of ferroelectric Hf 0.5 Zr 0.5 O 2 on graphene/Co/heavy metal epitaxial stacks is investigated via the implementation of several nucleation methods in atomic layer deposition. By employing in situ Al 2 O 3 as a nucleation layer sandwiched between Hf 0.5 Zr 0.5 O 2 and graphene, the Hf 0.5 Zr 0.5 O 2 demonstrates a remanent polarization (2Pr) of 19.2 μC/cm 2 . Using an ex situ, naturally oxidized sputtered Ta layer for nucleation, we could control 2Pr via the interlayer thickness, reaching maximum values of 28 μC/cm 2 with low coercive fields. Magnetic hysteresis measurements taken before and after atomic layer deposition show strong perpendicular magnetic anisotropy, with minimal deviations in the magnetization reversal pathways due to the Hf 0.5 Zr 0.5 O 2 deposition process, thus pointing to a good preservation of the magnetic stack including single-layer graphene. X-ray diffraction measurements further confirm that the highquality interfaces demonstrated in the stack remain unperturbed by the ferroelectric deposition and anneal. The proposed graphenebased ferroelectric/magnetic structures offer the strong advantages of ferroelectricity and ferromagnetism at room temperature, enabling the development of novel magneto-electric and nonvolatile in-memory spin−orbit logic architectures with low power switching.

Robust multiferroicity and magnetic modulation of the ferroelectric imprint field in heterostructures comprising epitaxial Hf0.5Zr0.5O2 and Co

“…This annealing results in a degradation of the interface between the ferroelectric oxide and the highly reactive ferromagnetic metal grown on top of it. Lancaster et al 32 reported state-of-the-art ferroelectric properties in Hf 0.5 Zr 0.5 O 2 adjacent to a graphene/Co/heavy metal stack. Large polarization values were only obtained while using an interface oxide layer, likely at the expenses of the magnetoelectric coupling.…”