Muon-spin relaxation and heat capacity measurements on the magnetoelectric and multiferroic pyroxenes LiFeSi2O6 and NaFeSi2O6

TL;DR

This study compares the magnetic properties of two pyroxene compounds, LiFeSi2O6 and NaFeSi2O6, using muon-spin relaxation and heat capacity measurements, revealing distinct magnetic structures despite structural similarities.

Contribution

It provides new insights into the differing magnetic ordering and complexity of magnetic structures in LiFeSi2O6 and NaFeSi2O6 through combined experimental techniques.

Findings

LiFeSi2O6 shows a single muon precession frequency and a single heat capacity peak at TN.

NaFeSi2O6 exhibits complex magnetic behavior with rapid depolarization and multiple phases.

Magnetic entropy mainly arises from correlations in Fe3+ chains.

Abstract

The results of muon-spin relaxation and heat capacity measurements on two pyroxene compounds LiFeSi2O6 and NaFeSi2O6 demonstrate that despite their underlying structural similarity the magnetic ordering is considerably different. In LiFeSi2O6 a single muon precession frequency is observed below TN, consistent with a single peak at TN in the heat capacity and a commensurate magnetic structure. In applied magnetic fields the heat capacity peak splits in two. In contrast, for natural NaFeSi2O6, where multiferroicity has been observed in zero-magnetic-field, a rapid Gaussian depolarization is observed showing that the magnetic structure is more complex. Synthetic NaFeSi2O6 shows a single muon precession frequency but with a far larger damping rate than in the lithium compound. Heat capacity measurements reproduce the phase diagrams previously derived from other techniques and demonstrate that the magnetic entropy is mostly associated with the build up of correlations in the quasi-one-dimensional Fe3+ chains.