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FESEM images of (a) uncoated ZnO NWs (UZO), (b) ZnO/Al2O3 (AZO), and (c) annealed (A-AZO) core-shell structured NWs. The scale bars are 300 nm. (d) and (e) Corresponding XRD patterns.
(a) M-H loops of UZO, AZO, and A-AZO NWs measured at 5 and 300 K. (b) Raw M-H data measured on the annealed core-shell nanowire sample A-AZO without subtracting the diamagnetic substrate contribution. The diamagnetic signal of a bare Si substrate is also shown. (c) M-H loops of a control sample of ZnAl2O4 nanocrystals. (d) RT M-H data of as-grown NWs (UZO) and three ZnO/Al2O3 core-shell samples (AZO) with various Al2O3 thickness: 5, 15, and 30 nm. (e) ZFC and FC temperature-dependent magnetization curves of A-AZO and AZO measured in the temperature range of 5–380 K. (f) M-T curve of the A-AZO sample in the extended temperature range of 5–780 K.
TEM images of individual NWs of (a) the as-grown sample (UZO), (b) after Al2O3 coating (AZO), and (c) the annealed Al2O3/ZnO core-shell nanowire sample (A-AZO). Insets show the corresponding SAED patterns and HRTEM images. The dashed line in the HRTEM image in (b) marks the Al2O3/ZnO interface. The thin solid line highlights the boundary of the rough ZnO nanowire core after reacting with the Al2O3 shell. (d) Close-up HRTEM image of an A-AZO NW, showing regions of stacking faults (S.F.) and distorted structures (D.S.) as well as the ZnAl2O4 phase at the interface area.
(a) Schematic illustration of the epitaxial interface between ZnO and ZnAl2O4 with their atomic crystal structures. (b) Illustration of the concept of producing magnetism in core-shell structured NWs of ZnO core wrapped by ZnAl2O4/Al2O3 shell. It is noted that the individual components exhibit mainly diamagnetism, but ferromagnetism emerges in nanostructures with engineered “spinterfaces.”
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