Fig. 4: Tunable magnetism in gZCO.
From: Tunable room-temperature ferromagnetism in Co-doped two-dimensional van der Waals ZnO
a Summary of temperature- and Co-concentration-dependent coercive fields in gZCO obtained by SQUID. With increased Co concentrations, gZCO can be tuned from paramagnetic (PM) to ferromagnetic (FM), and to less-ordered states. b–e M-H curves of Zn0.952Co0.048O/rGO (b), Zn0.927Co0.073O/rGO (c), Zn0.879Co0.121O/rGO (d), and Zn0.873Co0.127O/rGO (e), on the basis of SQUID measurements. From (b) to (d), the ferromagnetism becomes stronger. Optimal ferromagnetism has been realized when x = 0.121, with a pronounced coercive field 800 Oe at 2 K and 690 Oe at 350 K. When x = 0.127, a less-ordered magnetic state occurs, as evidenced by the shrunk coercive fields (e) and the suppressed magnetic moments at cryogenic temperatures (Supplementary Fig. S7b). Meanwhile, a higher magnetic field can be used to stabilize long-range order (Supplementary Fig. S7c). The less-ordered state can be explained by an interesting competition between ferromagnetic impurity-band-exchange interaction and antiferromagnetic superexchange interaction.
