Magnetic properties of nanoscaled paramelaconite Cu4O3-x (x=0.0 and 0.5)

Pure paramelaconite Cu4O3-x has been prepared in the form of nanoparticles with 56 nm in diameter. This mixed valency oxide crystallizes in a tetragonal lattice with 4 unit formulae and forms a pyrochlore structure which manifests in two stoichiometric forms; Cu4O3 and Cu4O2.5, the latter form having two oxygen vacancies per unit cell. Magnetic lattice consists of Cu spin 1/2, and both stoichiometric forms obey transition to the antiferromagnetic state at T-N=45-55 K. Defect free Cu4O3 is indicated by an inversion symmetry and exhibits both antiferromagnetic and ferromagnetic state, where the latter is supposedly due to the superexchange interaction in Cu-O(1n)-Cu bonds. An additional magnetic transition was observed in Cu4O3 at T=120 K, probably as a result of an incommensurate ordering. Absence of an inversion symmetry in the oxygen defect Cu4O2.5 results in a long range Dzyaloshinsky-Moriya interaction accompanied by the strong superparamagnetism. (C) 2014 Elsevier B.V. All rights reserved