Enhanced magnetism and time-stable remanence at the interface of hematite and carbon nanotubes

The interface of two dissimilar materials is well known for surprises in condensed matter, and provides avenues for rich physics as well as seeds for future technological advancements. We present some exciting magnetization (M) and remanence (μ) results, which conclusively arise at the interface of two highly functional materials, namely the graphitic shells of a carbon nanotube (CNT) and α-Fe₂O₃, a Dzyaloshinskii-Moriya interaction driven weak ferromagnet (WFM) and piezomagnet (PzM). We show that the encapsulation inside a CNT leads to a significant enhancement in M and correspondingly in μ, a time-stable part of the remanence, exclusive to the WFM phase. Up to 70% of in-field magnetization is retained in the form of μ at room temperature. The lattice parameter of the CNT around the Morin transition of the encapsulate exhibits a clear anomaly, confirming the novel interface effects. Control experiments on bare α-Fe₂O₃ nanowires bring into the fore that the weak ferromagnets such as α-Fe₂O₃ are not as weak, as far as their remanence and its stability with time is concerned, and encapsulation inside a CNT leads to a substantial enhancement in these functionalities.