Electronic Structures of Ge₂Sb₂Te₅/Co₂FeX (X: Al, Si) Interfaces for Phase Change Spintronics

Phase change materials (PCMs), such as Ge₂Sb₂Te₅, are highly attractive in modern electronics and photonics. However, their spintronic applications remain largely unexplored. Here, we propose a tentative modality of phase change spintronic devices based on the ferromagnet/PCM/ferromagnet structure. The electrically tunable properties of a PCM interlayer give rise to new possibilities of manipulating spin transport through phase change, adding new functionalities and modes of operation to the spintronic devices. As the first step toward realizing such phase change spintronic devices, we calculate the electronic structures of the interfaces of c-Ge₂Sb₂Te₅ and half-metallic ferromagnetic Co₂FeX (X: Al, Si). The interfaces are found not to be genuine half-metallic, indicating room for improvement. The band alignments are largely determined by the termination of c-Ge₂Sb₂Te₅. Two types of band alignments are found for c-Ge₂Sb₂Te₅/Co₂FeX interfaces. Considering c-Ge₂Sb₂Te₅ as heavily p-type-doped, interfaces with Te termination are generally suitable such that they offer low contact resistance for hole injection from Co₂FeX to c-Ge₂Sb₂Te₅ in the majority spin channel; at the same time, they naturally form tunneling barriers, alleviating the degradation of spin injection efficiency because of occasional hole injection in the minority spin channel. This work provides important insights into this proposed phase change spintronic framework.