Giant tunneling magnetoresistance, glassiness, and the energy landscape at nanoscale cluster coexistenceS. Kumar1, C. S. Mohapatra2 and P. Majumdar3
1 Institute for Physics, Theoretical Physics III, Electronic Correlations and Magnetism University of Augsburg - 86135 Augsburg, Germany
2 Department of Physics, I. I. T. Kharagpur - Kharagpur 721 302, India
3 Harish-Chandra Research Institute - Chhatnag Road, Jhusi, Allahabad 211 019, India
received 27 April 2005; accepted in final form 5 July 2005
published online 3 August 2005
We present microscopic results on the giant tunneling magnetoresistance that arises from the nanoscale coexistence of ferromagnetic metallic (FMM) and antiferromagnetic insulating (AFI) clusters in a disordered two-dimensional electron system with competing double exchange and superexchange interactions. Our Monte Carlo study allows us to map out the different field regimes in magnetotransport and correlate it with the evolution of spatial structures. At coexistence, the isotropic O(3) model shows signs of slow relaxation, and has a high density of low-energy metastable states, but no genuine glassiness. However, in the presence of weak magnetic anisotropy, and below a field-dependent irreversibility temperature Tirr, the response on field cooling (FC) differs distinctly from that on zero field cooling (ZFC). We map out the phase diagram of this "phase coexistence glass", highlight how its response differs from that of a standard spin glass, and compare our results with data on the manganites.
72.80.Ng - Disordered solids.
75.47.Gk - Colossal magnetoresistance.
75.50.Lk - Spin glasses and other random magnets.
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