Heat capacity signature of frustrated trimerons in magnetite

S Sahling,C Marin,J E Lorenzo,G Remenyi,V A Osipov,V L Katkov

doi:10.1038/s41598-020-67955-x

Abstract

Recently it has been proposed that the long-range electronic order formed by trimerons in magnetite should be frustrated due to the great degeneracy of arrangements linking trimerons. This result has important consequences as charge ordering from the condensed minority band electrons leads to a complex 3D antiferro orbital order pattern. Further more, the corner sharing tetrahedra structure of spinel B-sites supports frustration for antiferromagnetic alignments. Therefore frustration due to competing interactions will itself induce disorder and very likely frustration in the spin orientations. Here we present very low temperature specific heat data that show two deviations to the magnons and phonons contributions, that we analyze in terms of Schottky-type anomalies. The first one is associated with the thermal activation across both ferroelastic twin and ferromagnetic anti-phase domains. The second Schottky-type anomaly displays an inverse (1/H) field dependence which is a direct indication of the disordered glassy network with macroscopically degenerated singular ground states.

Highlights

It has been proposed that the long-range electronic order formed by trimerons in magnetite should be frustrated due to the great degeneracy of arrangements linking trimerons
The charge ordering (CO) developing below TV turns out to be more complex than initially thought and further studies have concluded that the actual CO is in the form of “trimerons”[6], with charge disproportionation amounting to 0.2 electrons among the B-sites
In addition three points were measured by the relaxation time method (RTM) at 0.084, 0.109 and 0.159 K showing that the results of the pulse method and the RTM are identical (See Supplementary Information)

Summary

Introduction

It has been proposed that the long-range electronic order formed by trimerons in magnetite should be frustrated due to the great degeneracy of arrangements linking trimerons. Recent electron holography and Lorentz microscopy e xperiments[8,9] have revealed a very complex network of interactions between the magnetic domains and the ferroelastic twin domains below TV , confirming previous results on a strong influence on the low temperature properties of magnetite. Magnetic after e ffect[3,10], ac-magnetic s usceptibility[11,12,13], and dielectric p ermitivity[14,15] experiments have shown the occurrence of glassy-like states below about 50 K All these susceptibilities exhibit strong frequency dependencies obeying Arrhenius activation laws, albeit of different attempt frequencies and activation energies. Specific heat experiments have reported a broad deviation to the Debye law with a maximum in the CP/T3 plot at 35 K

Methods

Results

Conclusion