Uncompensated-spins induced weak ferromagnetism in Ca3Mn2O7: Magneto-conductive and dual magneto-capacitive effects

Abstract Temperature dependent magnetization study on single phase orthorhombic Ruddlesden-Popper manganite Ca3Mn2O7 evidences antiferromagnetic (AFM) ordering below 123 K. Field-dependent magnetization M(H) depicts off-centered hysteretic loops below ~110 K—confirming the existence of both weak ferromagnetism (WFM) and exchange bias, whose development upon cooling is examined in detail. WFM is attributed to the formation of uncompensated-spin-clusters within the AFM-matrix, stabilized by the high-anisotropy in the manganite, favoring Dzyaloshinskii-Moriya (D-M) interaction. Temperature dependence of an evaluated average canting angle from the M(H) loops provides a quantitative measure of the WFM-evolution. Dielectric measurements exhibit magneto-conductive effects concurrent to the WFM-onset. Temperature dependence of the low-frequency/dc-limit of Jonscher-fits to the conductivity isotherms confirms the presence of relatively more-conductive clusters, embedded in the insulating-bulk. Nyquist impedance-analysis of complex impedance reveals two relaxations, yielding dual magnetic-field effects; the lumped circuit parameters feature anomalies across the magnetic phase changes.