Effect of Magnetic Field on the Growth of CoFe2O4 and NiFe2O4 Films

Abstract

Growing ferrite films of nanometers scale thickness requires several hours of time and involves utilization of sophisticated instrumentation. Generally, the films so fabricated require a substrate to grow on, and are incapable to stand freely without substrate support. Here, we report a technique to grow large-area, freestanding, transferrable ferrite (Cobalt and Nickel ferrite) films with a thickness ranging from ~ 67 to 591 nm, grown in about 20 minutes. The method, as a unique step, includes magnetic field assisted growth of the films to alter their properties. Nickel ferrite (NiFe2O4) films of tunable geometries are formed on the solution surface. The variation in the magnetic field strength applied during the formation process, give rise to the evolution of different structures on the surface of the films such as nanoparticles, nanopillars, and nanorods for the magnetic field strength of 1.25 Tesla, 1.50 Tesla, and 1.75 Tesla, respectively. Resultant different morphologies and the oriented growth of crystallites also affected the other properties of the films. The crystallite size varies from 23 to 27 nm with increasing the magnetic field strength from 1.25 to 1.75 T, and the optical band gap is found to decrease from ~ 4.0 eV to 3.45 eV with increase in strength of magnetic field. The magnetic parameters saturation (Ms) (11.45 to 106.25 emu/cm3), coercivity (Hc) (20.74 to 1032.95 Oe), and retentivity (Mr) (0.871 to 34.23 emu/cm3) also found to increase with the increasing magnetic field strength. The effect of temperature and magnetic field on the properties of the NiFe2O4 films were studied for which films in absence (unheated and heated) and in presence (unheated and heated) of the magnetic field were formed. Heating of the films resulted in the increased crystallite size from 7.3 to 22.3 nm in the film formed without magnetic field, and from 18.9 to 24.9 nm in the film formed under the influence of magnetic field. Applied magnetic field caused an increase in lattice constant and interplanar spacing, whil