Investigation of magnetic anisotropy of (Ge,Mn) nanocolumns

Thin films of Ge 1 − x Mn x containing Mn-rich nanostructures, so called nanocolumns, are grown by molecular-beam-epitaxy at low growth temperature ( T g ) on Ge(001) substrate. Depending on the growth temperature, these nanocolumns can be either crystalline or amorphous. A quantitative study of magnetic anisotropy of these nanocolumns is performed by superconducting quantum interference device and electron paramagnetic resonance. We present a correlation between the structural morphology (diamond lattice) and the magnetic properties in these nanocolumns. Crystalline (Ge,Mn) nanocolumns ( T g = 100 ° C ) exhibit fourth-order magnetic anisotropy due to the coupling between their magnetization and the cubic lattice whereas amorphous columns ( T g = 150 ° C ) only exhibit second-order shape anisotropy.