Effect of columnar defects on the pinning properties of NdFeAsO0.85 conglomerate particles

TL;DR

This study investigates how ion-induced columnar defects in NdFeAsO0.85 superconductors influence their magnetic pinning properties, showing temperature and field-dependent anisotropic effects that enhance critical current density.

Contribution

It demonstrates the creation of columnar defects via ion irradiation and analyzes their impact on vortex pinning and magnetic properties in NdFeAsO0.85.

Findings

Columnar defects are produced by 2 GeV Ta ion irradiation.

Pinning enhancement is anisotropic and temperature-dependent.

Columnar defects effectively suppress creep rate at certain conditions.

Abstract

Oxypnictide superconductor NdFeAsO0.85 sample was irradiated with 2 GeV Ta ions at a fluence of 5x10^10 ions/cm2. High resolution transmission electron microscopy study revealed that the irradiation produced columnar-like defects. The effect of these defects on the irreversible magnetisation in polycrystalline randomly oriented fragments was studied as a function of field angle and field sweep rate. We find that the critical current density is enhanced at fields below the matching field (~1 Tesla) but only marginally. The pinning enhancement is anisotropic and maximum along the defect direction at high temperatures but the pinning then becomes more isotropic at low temperatures. The creep rate is suppressed at high temperatures and at fields below the matching field, indicating the columnar defects are efficient pinning sites at these H and T conditions.