Toward flexible memory application: high-performance phase-change magnetic material Fe:GeTe films realized via quasi-van der Waals epitaxy

Phase-change materials (PCMs) have been widely investigated in terms of their application in non-volatile memory technology. However, flexible PCM films have been inadequately reported thus far owing to the thermal instability of most of the used flexible polymer substrates. In this study, we present a promising technology for flexible data storage: a direct fabrication of an epitaxial phase-change magnetic material (PCMM) Fe-doped GeTe (Fe:GeTe) film layer on a flexible mica substrate via quasi-van der Waals epitaxy (Q-vdWE). The flexible Fe:GeTe film on a mica substrate not only shows high epitaxial quality and stable ferromagnetism but also exhibits a basically preserved value of saturation magnetic moment (mu(s)) before, during, and after repeated bending. Detailed investigation of the phase change process induced by heat treatment and laser irradiation was performed on the Fe:GeTe films grown on mica, barium fluoride (BaF2), and silicon (Si) substrates. All the investigated Fe:GeTe films on any of the three substrates exhibit a fast reversible phase-change feature and different electrical and magnetic properties upon undergoing transitions between their crystalline and amorphous states. In contrast to those on rigid BaF2 and Si substrates prepared via conventional growth using strict structure matching, the epitaxial Fe:GeTe film integrated on a mica substrate shows remarkable mechanical durability, good signal repetition, and superior cycling endurance, which is considered to be correlated with Q-vdWE growth. The demonstration of an epitaxial PCMM film integrated on a mica substrate based on Q-vdWE paves a route to future flexible memory electronics.