Dipolar interactions in arrays of nickel nanowires studied by ferromagnetic resonance

Using a planar microstrip transmission line, the dipolar interactions in electrodeposited Ni nanowires arrays are characterized as a function of the membrane porosity (4% to 38%) and the wire diameter (56 to 250 nm). The dipolar interactions between the wires can be modeled in a mean-field approach as an effective uniaxial anisotropy field oriented perpendicular to the wire axis and proportional to the membrane porosity. The dipolar interaction field opposes the self-demagnetization field of an isolated single wire which keeps the magnetization parallel to the wire axis. An increase in the porosity therefore induces a switching of the effective anisotropy easy axis from parallel to perpendicular to the wire axis above a critical porosity of 35-38% independent of the wire diameter.