Correlation between magnetism and the Verwey transition in magnetite

Seeking to unravel the enigmatic Verwey transition and its interplay with magnetism, we have conducted comprehensive measurements on the temperature-dependent electrical resistivity and magnetic moment of stoichiometric and doped-magnetite single crystals at temperatures reaching 1000 K. These investigations have allowed us to identify the Curie temperature, $T_C$, and other characteristic temperatures of the electrical resistivity. Remarkably, we have identified correlations between these temperatures and the Verwey temperature, $T_V$, indicating that the electrical transport properties and the mechanism of the Verwey transition are closely related to the magnetic properties.

💡 Research Summary

This work investigates the long‑standing question of how the Verwey metal‑insulator transition (TV) in magnetite (Fe3O4) is linked to its ferrimagnetic Curie transition (TC). The authors measured temperature‑dependent magnetization and electrical resistivity on fifteen single‑crystal specimens, including stoichiometric material and crystals doped with Zn, Mn, Al, or Ti on either the tetrahedral (A) or octahedral (B) sites. Magnetization was recorded from 300 K to 1000 K in a 100 Oe field, allowing precise determination of TC. Resistivity was measured over the same range and four characteristic temperatures were extracted: TM (resistivity minimum around 300–400 K), TI (first high‑temperature inflection), TRMAX (resistivity maximum near 750–780 K) and TRINF (subsequent high‑temperature inflection).

The data show that increasing dopant concentration systematically lowers TV from ~122 K (stoichiometric) down to below 72 K (Ti‑doped) and, simultaneously, reduces TC from ~854 K to ~800 K. The high‑temperature resistivity markers TRMAX and TRINF follow the same trend, decreasing as TV decreases. This correlation holds regardless of dopant type or lattice site, suggesting a universal coupling among electronic, lattice, and magnetic degrees of freedom in magnetite.

The authors interpret the results in terms of magnetic polarons and trimerons that form already at TC. These entities modify the A‑B superexchange (JAB) and B‑B double‑exchange (JBB) interactions, thereby preparing the electronic environment for the Verwey transition. At temperatures above TV, a redistribution of Fe2+ and Fe3+ between A and B sites occurs, reflected in the resistivity maximum (TRMAX) and subsequent inflection (TRINF). The study also discusses pressure effects: hydrostatic pressure lowers TV but raises TC, whereas uniaxial stress can increase TV, highlighting the complex role of lattice strain.

While the correlation between TC, TV, TRMAX, and TRINF is clear, the authors note that TM and TI are more sensitive to the specific dopant and may not serve as intrinsic indicators. They suggest that future work combining neutron scattering, X‑ray spectroscopy, and ultrafast optical probes could directly observe the dynamics of trimeron and polaron formation, providing deeper insight into the intertwined magnetic and electronic transitions.

In summary, extensive high‑temperature magnetization and transport measurements across a broad doping series establish a robust experimental link between the Verwey transition temperature, the Curie temperature, and characteristic high‑temperature resistivity features, underscoring the coupled nature of electronic, structural, and magnetic phenomena in magnetite.