On the Paramagnetic Impurity Concentration of Silicate Glasses from Low-Temperature Physics

TL;DR

This paper refines the measurement of paramagnetic impurity concentrations in silicate glasses by accounting for tunneling currents caused by structural inhomogeneities, improving accuracy over previous methods.

Contribution

It introduces a method to include tunneling current effects in SQUID magnetization measurements, aligning impurity concentration estimates with heat capacity data.

Findings

Including tunneling effects improves impurity concentration estimates.

Neglecting tunneling currents leads to overestimation of impurities.

Supports the structural inhomogeneity theory of magnetic effects in glasses.

Abstract

The concentration of paramagnetic trace impurities in glasses can be determined via precise SQUID measurements of the sample's magnetization in a magnetic field. However the existence of quasi-ordered structural inhomogeneities in the disordered solid causes correlated tunneling currents that can contribute to the magnetization, surprisingly, also at the higher temperatures. We show that taking into account such tunneling systems gives rise to a good agreement between the concentrations extracted from SQUID magnetization and those extracted from low-temperature heat capacity measurements. Without suitable inclusion of such magnetization contribution from the tunneling currents we find that the concentration of paramagnetic impurities gets considerably over-estimated. This analysis represents a further positive test for the structural inhomogeneity theory of the magnetic effects in the cold glasses.