Tuning of optical bandgap and magnetization of CoFe2O4 thin films

Abstract

Single phase CoFe2O4 thin films are deposited on quartz substrates at 400 °C using ultrasonic assisted chemical vapor deposition, and the tuning of optical bandgap and saturation magnetization of films is demonstrated by varying the post deposition annealing temperature. The optical band gap varies from 1.58 to 1.41 eV and saturation magnetization increases from 4 to 46 emu/g as the post deposition annealing temperature is increased from 500 °C to 700 °C. The observed change in optical bandgap and the magnetic properties is attributed of the shifting of Co2+ from the octahedral to the tetrahedral site with the increase in the annealing temperature. Raman studies of the films support the redistribution of Co2+ among the octahedral and tetrahedral sites in CoFe2O4 films with the increase in the annealing temperature.

Valence Change Bipolar Resistive Switching Accompanied With Magnetization Switching in CoFe2O4 Thin Film

“…The net magnetization of CFO is given as; M S = M B -M A , where M A and M B are net magnetic moments at “A” and “B” sites 50 . The relative change in magnetic moments of site “A” and “B” can alter the net magnetic moment of cobalt ferrite 51 . There can be two possible cases: the oxygen vacancies can reduce the cations present in (i) “A” site or (ii) “B” site.…”

Low field magneto-tunable photocurrent in CoFe2O4 nanostructure films for enhanced photoelectrochemical properties

“…The energy width between e g and t 2 g levels is higher at the octahedral sites (Δ o ) as compared to the tetrahedral sites (Δ t ) and is given as 27,34 ; . As, in CoFe 2 O 4 , Co 2+ ions can reside at the octahedral sites or at the tetrahedral sites and the optical bandgap is strongly dependent upon the relative population of Co 2+ ions at the octahedral and the tetrahedral sites.…”

“…As, in CoFe 2 O 4 , Co 2+ ions can reside at the octahedral sites or at the tetrahedral sites and the optical bandgap is strongly dependent upon the relative population of Co 2+ ions at the octahedral and the tetrahedral sites. It is reported 27 that the shifting of Co 2+ ions from the octahedral sites towards the tetrahedral sites results in the decrease in the optical bandgap of CoFe 2 O 4 . Thus, in the present case, it is expected that under the effect of magnetic field the strain gets produced due to magnetostrictive properties of CoFe 2 O 4 .…”

“…However, due to a large amount of empty interstitial sites, a small fraction of the Co 2+ ions can also occupy the tetrahedral sites 22 . The electrical and optical properties of CoFe 2 O 4 can be tuned depending upon the relative distribution of metal ions (Co 2+ and Fe 3+ ) at the tetrahedral and octahedral sites 26,27 . It can also possess soft magnetic properties at nanoscale due to which low magnetic field will be required to tune the charge transport properties 28–30 .…”

Tailoring the optical bandgap and magnetization of cobalt ferrite thin films through controlled zinc doping

“…6 Among the various ferrites, cobalt ferrite (CFO) is a promising candidate because of its large anisotropy, 7 saturation magnetization, 8 high coercivity 9 and remanence. 10 Cobalt ferrite exist in inverse spinel or partially inverse spinel structure with formula AB 2 O 4 (A= Fe, B= Co, Fe), where Co 2+ occupy the octahedral site and half of the Fe 3+ occupy octahedral site and remaining half of Fe 3+ occupy the tetrahedral site but the distribution of these metal ions depend upon many factors such as strain 11 and temperature 12 etc. The optical properties of cobalt ferrite are due to the d-d transition which has been shown to have a strong temperature dependency because of the spin charge coupling effect.…”