Giant Tunneling Magnetoresistance, Glassiness, and the Energy Landscape at Nanoscale Cluster Coexistence

TL;DR

This paper investigates the microscopic origins of giant tunneling magnetoresistance in a disordered 2D electron system with coexisting ferromagnetic metallic and antiferromagnetic insulating clusters, revealing complex magnetic behaviors and a novel phase coexistence glass.

Contribution

It provides the first microscopic analysis of magnetotransport and glassy behavior in nanoscale phase coexistence, highlighting the effects of magnetic anisotropy and mapping the phase diagram.

Findings

Giant tunneling magnetoresistance arises from nanoscale phase coexistence.

Presence of a phase coexistence glass with distinct magnetic response.

Identification of a phase diagram with a new glassy magnetic state.

Abstract

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 $T_{irr}$, 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.