Crystal growth and theorical calculations of titanomagnetite and titanohematite series

In geological studies, the titanomagnetite series (Fe_3-xTi_xO₄) and the titanohematite series (Fe_2-yTi_yO₃) are widely used for paleomagnetic identification, as variations in Ti content significantly affect their magnetic properties, thereby controlling the preservation of paleomagnetic signals. In this study, titanomagnetite and titanohematite series with different Ti contents were synthesized via a hydrothermal method to investigate their crystal growth mechanisms under varying Ti contents. Iron hydroxide precursors formed first and, upon heating, transformed into corundum or inverse spinel structures with Ti incorporated into the lattice. XRD results indicate that the precursor is an amorphous phase, and that the synthesized titanohematite samples consist of pure-phase titanohematite. XPS analysis shows that the relative ratio of Ti and Fe in titanohematite correspond to approximately y = 0.2, which the SEM–EDS analysis confirms the incorporation of Ti into the samples. SQUID measurements further demonstrate that low-Ti-content titanohematite exhibits antiferromagnetic behavior.

In addition, density functional theory (DFT) calculations were performed to optimize the structures and to evaluate the magnetic moments and band gaps of titanomagnetite and titanohematite series with different Ti contents. For the former series at x = 1, GGA calculations reveal that the inverse spinel structure is preserved, but with antiferromagnetic ordering while noting that the band gap was underestimated. When x = 0.5, Ti atoms partially occupy tetrahedral sites, leading to pronounced effects on the structural stability and magnetic properties. For the latter series, GGA+U calculations show that no significant structural changes are observed with increasing Ti concentration. However, a net magnetic moment emerges at y = 0.5, demonstrating that Ti incorporation beyond a critical proportion alters the cation distribution, consequently affecting the total magnetic moment.

Integrating hydrothermal synthesis parameters, crystal growth mechanisms, structural characteristics, and magnetic properties of both titanomagnetite and titanohematite series, this study provides new insights into the interpretation of paleomagnetic behavior and also offers a theoretical basis for potential applications in photocatalytic materials.