Intrinsic magnetic properties of BixCo2−xMnO4 spinels obtained by short-time etching

Abstract We report the structural and magnetic properties of Co 2 MnO 4 , partially substituted by Bi at the octahedral site. Bismuth enhances ferromagnetism due to a decrease of the Co 2+ –Co 2+ antiferromagnetic interactions and an increase of the Mn 3+ –Mn 4+ exchanges. Spurious phases (magnetic and/or nonmagnetic oxides) can easily form because of the large differences between the ionic radii of Bi 3+ and Co 3+ , hiding or altering the intrinsic physical properties of the main Bi x Co 2− x MnO 4 phase. An easy way to eliminate the secondary phases is using acid reagents. Short-time etching of Bi 0.1 Co 1.9 MnO 4 using nitric acid was successfully used, keeping most of the properties of the initial compound, with no alteration of the crystallographic structure. Final stoichiometry was respected (∼Bi 0.08 Co 1.82 MnO 4 ), meaning that the material after etching definitely contains bismuth elements in its structure and the observed properties are intrinsic to the oxide spinel. Additional experiments were performed as a function of the synthesis conditions, showing that an optimal pH value of 7 allowed the best magnetic response of the non-doped material.