Unveiling superferromagnetic polar state in inhomogeneous nanoisland FeNi films featuring anomalously strong planar diamagnetic response near percolation transition

Magnetic properties of inhomogeneous nanoisland FeNi films were studied by SQUID magnetometry. In the superferromagnetic phase the magnetization response exhibited remarkable anisotropy, with anomalously large polar magnetization in the applied magnetic filed, which decreases approaching the film percolation transition. The in-plane response showed ferromagnetic saturation behavior, competing with diamagnetic-like response, which became pronounced at large magnetic fields. We found anomalously strong diamagnetic-like response near the film percolation transition, where the effective volume susceptibility can be estimated as chi^{cgs}_V = 0.026 pm 0.006. The observed behavior is discussed in terms of the non-superconducting diamagnetic state related to the inhomogeneous distribution of the toroidal moment density.