Magnetization-induced chirality in second harmonic generation response of U-shaped permalloy nanostructures

Magnetization-induced circular dichroism (CD) in optical second harmonic generation (SHG) is observed in planar symmetrical arrays of U-shaped permalloy nanostructures. We demonstrate that extrinsic chirality of an array leads to the CD effect that strongly depends on the azimuthal orientation of the sample. In the absence of magnetization, the value of the SHG CD effect averaged over $2\pi$ azimuthal angle is zero, while up to 6% averaged SHG CD appears as the dc magnetic field is applied along the symmetry axis of the structure. Importantly the averaged SHG CD effect changes its sign under the reversal of the magnetic field, which corresponds to the appearance of magnetization driven true chirality in an array of symmetric magnetic nanostructures.

Figure 1

(a) SEM image of the sample under study; (b) scheme of the SHG experiment.

Figure 2

Azimuthal dependencies of the circular dichroism of the $s$ (right panel) and $p$ (left panel) polarized SHG measured in the absence of the dc magnetic field, angle of incidence is $\theta ={20}^{\circ }$. The orientation of the U-shaped nanoelement for the azimuthal position $\psi =0^{\circ }$ is shown schematically in the inset. Solid line is the result of the approximation for the m-symmetric structure.

Figure 3

Azimuthal dependencies of the circular dichroism of the $s$ (right panel) and $p$ (left panel) polarized SHG with applied magnetic field in the right (red dots) and left (blue dots) directions, angle of incidence $\theta ={20}^{\circ }$.