Anomalous organic magnetoresistance from competing carrier-spin-dependent interactions with localized electronic and nuclear spins

TL;DR

This paper uncovers a new low-field magnetoresistance regime in organic semiconductors caused by the interplay of localized nuclear and electronic spins, revealing doping-dependent effects on magnetoresistance.

Contribution

It introduces a theoretical model explaining how carrier spin dynamics influence magnetoresistance in organic semiconductors with localized spins.

Findings

Magnetoresistance is suppressed by doping initially.

A doping regime exists where magnetoresistance remains unaffected.

High doping fully suppresses magnetoresistance.

Abstract

We describe a new regime for low-field magnetoresistance in organic semiconductors, in which the spin-relaxing effects of localized nuclear spins and electronic spins interfere. The regime is studied by the controlled addition of localized electronic spins to a material that exhibits substantial room-temperature magnetoresistance ($\sim 20$\%). Although initially the magnetoresistance is suppressed by the doping, at intermediate doping there is a regime where the magnetoresistance is insensitive to the doping level. For much greater doping concentrations the magnetoresistance is fully suppressed. The behavior is described within a theoretical model describing the effect of carrier spin dynamics on the current.