Emergence of a high T_c magnetic phase in a time-elapsed vdW magnet

Long-range magnetic order in van der Waals (vdW) materials, exfoliated in few atomic layers, can be tuned via application of electric/magnetic field, interface engineering or even by chemical substitution/doping. Usually, active surface oxidation due to the exposure in the ambient condition causes degradation of 2D magnetic flakes which, in turn, affects the electronic/spintronic device performance in nanoscale. Counterintuitively, our current study reveals that exposure to the air at ambient atmosphere results in advent of a stable secondary ferromagnetic phase in the form of Cr₂Te₃ (T_C2 ~ 160 K) in the parent vdW magnetic semiconductor Cr₂Ge₂Te₆ (T_C1 ~ 69 K) [1]. As a result, the magnetic anisotropy energy (MAE) gets enhanced in the hybrid system by an order compared to the pristine Cr₂Ge₂Te₆, increasing the stability of the ferromagnetic ground state with time. The coexistence of the two ferromagnetic phases is confirmed through systematic investigation of crystal structure along with detailed dc/ac magnetic susceptibility, specific heat, Raman spectroscopy and magneto-transport measurements. In contrast to rather common poor environmental stability of the vdW magnets, our results open possibilities of finding air-stable novel materials having multiple magnetic phases [2].