One-pot synthesis of Mn3O4-decorated GaN nanowires for drastic changes in magnetic and gas-sensing properties

•Novel composite nanowires have been synthesized with Mn3O4 structures being coated on the surface of the GaN nanowires.•The addition of Mn3O4 shell nanostructures significantly enhanced the gas-sensing sensitivity.•The addition of Mn3O4 shell turned the n-type sensing characteristic of the pure GaN nanowires into the p-type one.•The presence of Mn3O4 provided an acceptable ferromagnetic ability.

Composite nanowires consisting of GaN and Mn3O4 were prepared via a one-step method, wherein a mixture of GaN and Mn powders was thermally heated under flowing ammonia gas at 900 °C. Scanning electron microscopy indicated that the nanowire diameter increased with increasing growth temperature. The growth mechanism of composite nanowires at 900 °C is mainly related to a vapor–solid or base-growth process, whereas the 700 °C-grown product corresponded to pure GaN nanowires synthesized by means of a tip-growth vapor–liquid–solid process. With pure GaN nanowires exhibiting weak ferromagnetism at 5 K, the ferromagnetic behavior was significantly enhanced by employing the GaN/Mn3O4 composite nanowires. We suggest that the Mn3O4 shell plays a role in enhancing the ferromagnetic behavior of composite nanowires. Room-temperature sensing of H2 gas revealed that the addition of Mn3O4 shell turned the n-type sensing characteristic of the pure GaN nanowires into the p-type one. The conversion is related to the p-type nature of the Mn3O4 phase, which provides the continuous path of hole currents. The significant enhancement of sensing behavior by employing the GaN/Mn3O4 composite nanowires is due to not only the relatively small volume of the Mn3O4 structures but also the presence of p-type Mn3O4/n-type GaN heterojunctions.

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