On the pinning force in high density MgB₂ samples.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Understanding flux pinning mechanisms is crucial for optimizing superconducting materials like MgB₂.
• High-density sintered MgB₂ samples exhibit complex behaviors in their field dependence of pinning forces.
• Standard scaling procedures often fail to accurately describe the observed pinning force profiles in these materials.

Purpose of the Study:

• To analyze the field dependence of pinning forces in various high-density sintered MgB₂ samples.
• To investigate the applicability of the Dew-Hughes scaling law using a percolation model.
• To identify factors governing the transition between dissipative and non-dissipative current transport in high magnetic fields.

Main Methods:

• Experimental analysis of field dependence of pinning force in pure, doped, and partially oriented MgB₂ samples.
• Application of a percolation model incorporating a connecting factor for grain superconductivity.
• Comparison of experimental data with Dew-Hughes scaling law predictions.

Main Results:

• The percolation model, with a grain connectivity factor, successfully explains most features of the critical force field dependence.
• The connecting function, influenced by superconducting anisotropy, dictates the boundary between dissipative and non-dissipative transport.
• Experimental data reveals the connecting function's dependence on sample-specific properties (stoichiometry, defects, homogeneity) and its characteristic peaked shape.

Conclusions:

• The Dew-Hughes scaling law is applicable to grain boundary pinning in MgB₂ when considering grain connectivity via a percolation model.
• Superconducting anisotropy and sample-specific microstructural properties significantly influence current transport behavior in magnetic fields.
• The connecting function provides a unified framework for understanding dissipation in diverse MgB₂ samples.