Magneto-transport and glassiness at nanoscale coexistence

Sanjeev Kumar

Institute for Physics, University of Augsburg

Motivated by experiments on the phase separated manganites, we study a model of competing double-exchange and superexchange in the presence of quenched disorder in two dimensions (2D). Using a new Monte-Carlo scheme we are able to access the spatially inhomogeneous magnetic and electronic state that emerges from the interplay of disorder and interactions. We map out the thermal and field evolution of the spatial structures and the magnetic state, and demonstrate the various metal-insulator crossovers in this model. In addition to cluster formation, we discover signatures of slow relaxation in the coexistence regime and are able to correlate it with the existence of a high density of low energy metastable configurations. On introducing weak uniaxial anisotropy the slow relaxation is converted to clear irreversibility, with the field cooled (FC) response differing distinctly from the zero field cooled (ZFC) response. We contrast the properties of this 'phase coexistence glass' to canonical spin glass and cluster glasses, and compare our results with experiments on the manganites