λ-MnO2, a new frustrated antiferromagnet with the defect spinel structure (abstract)

MnO2 exists in a number of crystalline modifications. λ-MnO2, prepared by electrochemical delithiation of the spine Li2Mn2O4, has Mn4+, S=3/2, occupying the octahedral (16c) sites in Fd3m. The magnetic sublattice consists of a pyrochlore-type array of corner-shared tetrahedra and is thus a candidate for frustrated antiferromagnetism. The dc susceptibility data indicate, for very low applied fields of 45 G, a sharp maximum at 32 K but this is …