MOKE spectra and ultrahigh density data storage perspective of FePt nanomagnet arrays

Superlattices of self-assembled, monodisperse FePt nanomagnet arrays have been studied using magneto-optical (MOKE) spectroscopy in the photon energy range 0.8-5.3 eV. The nano-magnets are chemically synthesized and subsequently deposited on SiO₂ substrates for structural, magnetic and optical characterization. Large room temperature coercivities up to 9000 Oe are obtained after annealing to temperatures up to 580°C. They are attributed to the transformation from the chemically disordered fcc phase to the chemically ordered L1₀ fct phase of FePt. The chemical ordering process is accompanied by changes in the electronic structure of the materials, which leads to characteristic MOKE spectral changes. In particular, the occurrence of a strong MOKE peak at 2 eV photon energy is observed. Polar and transverse (out-of-plane and in-plane) Kerr hysteresis studies indicate 3D random distribution of the magnetic easy axes in these superlattices. These nanomagnet assemblies with the control on magnet spacing and spatial order are prospective candidates for future ultrahigh density magnetic recording media with potential areal densities beyond Tbit/in².