Effects of proton irradiation and ageing on the superconducting properties of single crystalline and polycrystalline MgB2

TL;DR

This study investigates how proton irradiation and aging affect the superconducting properties of MgB2, revealing enhanced pinning and increased upper critical field after irradiation and aging, with some trade-offs in transition temperature.

Contribution

It provides new insights into the effects of proton irradiation and long-term aging on MgB2's superconducting properties, including critical current density and upper critical field.

Findings

Irradiation induces a peak in critical current density near Hc2.

Aging enhances the peak effect and doubles Hc2, with a slight T_c reduction.

Polycrystalline MgB2 shows temporary improvements that revert after two years.

Abstract

We present magnetisation data on crystalline and polycrystalline MgB2 before and after irradiation with ~1MeV protons. In the virgin crystal the critical current density is below our noise floor of 103A/cm2 over most of the field range. However, after irradiation a peak occurs in the current density as a function of applied magnetic field as the upper critical field Hc2 is approached. After subsequent ageing over a time period of three months, the peak effect is greatly enhanced, exhibiting much stronger pinning over a wide field range, and the upper critical field is approximately doubled, accompanied by a 2K reduction in transition temperature. Similar studies were made on polycrystalline fragments, where irradiation leads to an increased irreversibility field (Jc is enhanced at high fields but decreased at low fields) and a suppression in transition temperature. However, after two years of ageing both parameters returned towards those of the virgin sample.