Incorporation of cobalt ions into magnetoelectric gallium ferrite epitaxial films: tuning of conductivity and magnetization

Abstract

Thin films of Ga 0.6 Fe 1.4 O 3 show ferrimagnetism with a transition temperature at around 360 K but suffer from large charge conduction. Substituting Fe 2+ with non-magnetic Mg 2+ ions reduces the charge conduction but also lowers the magnetic transition temperature. Doping Ga 0.6 Fe 1.4 O 3 thin films with magnetic Co 2+ ions leads to a similar reduction in the charge conduction, which is significant by two orders of magnitude, and, on the other hand, does not lead to any modification of the ferrimagnetic transition. The remnant magnetization of the leakage currents free Co-doped Ga 0.6 Fe 1.4 O 3 thin films is of 53 emu cm À3 at 300 K. These films, therefore, are promising materials with potential uses in magnetoelectric and multiferroic devices.

Effect of annealing atmosphere on leakage and dielectric characteristics of multiferroic gallium ferrite

“…However, in polycrystalline bulk and thin film forms, GFO suffers from high electrical leakage which needs to be improved for any prospect of its realization in practical applications. There have been a few studies on improving the leakage characteristics of GFO by atomic substitution such as Mg, Co and Zn, by modifying the defect chemistry . Among these, Mg‐doping of GaFeO 3 thin films has been shown to result in an improved leakage behavior, albeit no ferroelectric loops were reported .…”

Control of electrical leakage in magneto‐electric gallium ferrite via aliovalent substitution

“…Similar observations were made for Mg 2+ ‐doped GFO thin films where minimum leakage current density was found at a Mg concentration of 2.8%, attributed to the tuning of charge carriers from n ‐type to p ‐type as well as to variation in the density of charge carriers . The substitution of Co 2+ ions also allowed reduction in conductivity in case of GFO thin films by suppressing the direct hopping between Fe 2+ /Fe 3+ ions . A fitting of data on log scale yielded the slope for conduction considering the relation J ∝ V α .…”

“…25 The substitution of Co 2+ ions also allowed reduction in conductivity in case of GFO thin films by suppressing the direct hopping between Fe 2+ /Fe 3+ ions. 9 A fitting of data on log scale yielded the slope for conduction considering the relation J ∝ V α . Here, α equal to 1 depicts an Ohmic conduction and α > 1…”

“…However, it is an antiferromagnet and hence exhibits negligible remnant magnetization. Also, it exhibits very small coupling between the electrical and magnetic order parameters curtailing its potential for magnetoelectric devices . BiMnO 3 (BMO) is another interesting material exhibiting both ferroelectric and ferromagnetic ordering but has very low ferroelectric transition temperature of ~105 K which is a major impediment in realizing any practical devices …”

“…Similar strategies have also been adopted for GFO, albeit to a very limited extent. Researchers have attempted the site engineering concept, for example, doping at A(Ga)– and B(Fe)–sites in GFO . For example, a decreased propensity of hopping between Fe 2+ and Fe 3+ sites upon Mg 2+ doping on Ga‐site in GFO thin films was a primary cause behind reduced electrical leakage in Mg‐doped films .…”