Nanocrystalline zinc ferrite films studied by magneto-optical spectroscopy

Abstract

Ferrimagnetic Zn-ferrite (ZnFe2O4) films can be grown with the ferromagnetic resonance linewidth of 40 Oe at 9.5 GHz without going through a high temperature processing. This presents interest for applications. The work deals with laser ablated ZnFe2O4 films deposited at O2 pressure of 0.16 mbar onto fused quartz substrates. The films about 120 nm thick are nanocrystalline and their spontaneous magnetization, 4πM s, depends on the nanograin size, which is controlled by the substrate temperature (T s). At T s ≈ 350 °C, where the grain distribution peaks around ∼20–30 nm, the room temperature 4πM s reaches a maximum of ∼2.3 kG. The films were studied by magnetooptical polar Kerr effect (MOKE) spectroscopy at photon energies between 1 and 5 eV. The complementary characteristics were provided by spectral ellipsometry (SE). Both the SE and MOKE spectra confirmed ferrimagnetic ordering. The structural details correspond to those observed in MgFe2O4 and Li0.5Fe2.5O4 spinels. SE experiments confirm the insulator behavior. The films display MOKE amplitudes somewhat reduced with respect to those in Li0.5Fe2.5O4 and MgFe2O4 due to a lower degree of spinel inversion and nanocrystalline structure. The results indicate that the films are free of oxygen vacancies and Fe3+-Fe2+ exchange.