Evidence for electromagnetic granularity in polycrystalline Sm1111 iron-pnictides with enhanced phase purity

TL;DR

This study investigates the effects of phase purity and density on the current-carrying capabilities of polycrystalline Sm1111 iron-pnictides, revealing intrinsic granularity similar to cuprates despite improved purity.

Contribution

It demonstrates that even highly pure and dense Sm1111 samples exhibit intrinsic electromagnetic granularity, advancing understanding of their current transport limitations.

Findings

Enhanced phase purity increases intergranular current density.

HIPping reduces Tc and intragranular current density due to fluorine loss.

Samples remain intrinsically granular despite improved purity.

Abstract

We prepared polycrystalline SmFeAsO1-xFx (Sm1111) bulk samples by sintering and hot isostatic pressing (HIP) in order to study the effects of phase purity and relative density on the intergranular current density. Sintered and HIPped Sm1111 samples are denser with fewer impurity phases, such as SmOF and the grain boundary wetting phase, FeAs. We found quite complex magnetization behavior due to variations of both the inter and intragranular current densities. Removing porosity and reducing second phase content enhanced the intergranular current density, but HIPping reduced Tc and the intragranular current density, due to loss of fluorine and reduction of Tc. We believe that the HIPped samples are amongst the purest polycrystalline 1111 samples yet made. However, their intergranular current densities are still small, providing further evidence that polycrystalline pnictides, like polycrystalline cuprates, are intrinsically granular.