Magnetization and magnetoresistance of Ni/nanoporous-GaN composites.

Multifunctional semiconductors widen the application scope of existing semiconductor devices. Here we report on the ferromagnetic/semiconductor coupling obtained through nickel and porous-GaN composites. We realised nickel-infiltrated and nickel-coated porous-GaN structures, and examined the subsequent magnetic and magnetotransport properties. We found that the magnetization of the porous-GaN/Ni composites strongly depended on the amount of deposited nickel and evolves from relatively isotropic and remanent (up to 90% remanent-to-saturation magnetization) response to an anisotropic response characteristic of thin-films. The magnetoresistance of nickel sputter-coated porous-GaN structures was measured at 300 and 200 K. The temperature dependant measurements suggested that transport in the GaN layers is dominating the current. Nonetheless, depending on sample pore size, the magnetoresistance displayed high (12-fold) out-of-plane/in-plane anisotropy, and significant hysteresis. These results are uncharacteristic of GaN transport and point towards magneto-piezo-resistive coupling between the nickel and the porous GaN. These results encourage deeper investigation of magnetic nanostructure property tuning and of magnetic property coupling to GaN and similar materials.