  We studied the magnetic properties of ferromagnetic-semiconductor composites
based on nickel and porous-GaN, motivated by the effort to couple magnetic and
semiconductor functionality. Nickel-infiltrated and nickel-coated (laminated
thin-film) porous GaN structures were fabricated by electrodeposition, and
their magnetic properties were subsequently examined collectively, by vibrating
sample magnetometry and on the nanoscale, by magnetic force microscopy. We
successfully demonstrated the ability to realize nickel infiltrated porous GaN,
where the magnetic properties were dominated by the infiltrated material
without a measurable surface contribution. We found that the structure and
magnetization of electrodeposited porous-GaN/Ni composites depended on GaN
degree of porosity and the amount of deposited nickel. The magnetization
evolves from a nearly isotropic response in the infiltrated structures, to a
shape-anisotropy controlled magnetic thin-film behaviour. Furthermore, both
infiltrated and thin-film nickel electrodeposited on porous GaN were found to
have low (< 0.1%) strain and corresponding low coercivity: < 6.4 and < 2.4 kA/m
for infiltrated and thin-film, correspondingly. The most likely cause for the
lowered strain is increased compliance of the porous GaN compared to bulk.
These results encourage deeper investigation of magnetic nanostructure property
tuning and of magnetic property coupling to GaN and similar materials.
