Gigantic plasmon resonance effects on magneto-optical activity of molecularly thin ferromagnets near gold surfaces

We report on a new magneto-plasmonic material consisting of 1 nm thick ferromagnetic nanosheets and Au nanoparticles. The magneto-optical (MO) Kerr spectra of Ti0.8Co0.2O2 nanosheets near Au surfaces showed a gigantic MO response (∼106 deg cm−1) in the visible wavelength region (380–600 nm), not present in Ti0.8Co0.2O2 nanosheets on a bare glass substrate. The observed peaks correspond to intrinsic d–d* electronic transitions in Ti0.8Co0.2O2 and are consistent with the near-field enhancement of the MO response resulting from the spectral overlap of the surface-plasmon-resonance (SPR) in the Au surface with the electronic transitions in Ti0.8Co0.2O2. Similar SPR effects were also achieved in ferromagnetic nanosheet/Au with different compositions and with different separation distances (<5 nm). This demonstration of SPR-enhanced magneto-optics in the ferromagnetic/plasmonic nanosystem may enable designing of nanoarchitectures for miniaturized high-performance MO devices and for remote sensing and imaging of magnetic fields.