Chiral mesostructured hematite with temperature-independent magnetism due to spin confinement

Hematite (α-Fe₂O₃) is known to undergo conversion from weak ferromagnetic to antiferromagnetic as the temperature decreases below the Morin temperature (T_M = 250 K) due to spin moment rotation occurring during the Morin transition (MT). Herein, we endowed hematite with mesostructured chirality to maintain weak ferromagnetism without MT. Chiral mesostructured hematite (CMH) nanoparticles were prepared by a hydrothermal method with glutamic acid (Glu) as the symmetry-breaking agent. The triangular bipyramidal CMH nanoparticles were composed of helically cleaved nanoflakes with twisted crystal lattice. Field-cooled (FC) magnetization measurements showed that the magnetic moments of CMH were stabilized without MT within the temperature range of 10–300 K. Hysteresis loop measurements confirmed the weak ferromagnetism of CMH. The enhanced Dzyaloshinskii–Moriya interaction (DMI) was speculated to be responsible for the temperature-independent weak ferromagnetism, in which the spin configuration would be confined with canted antiferromagnetic coupling due to the mesostructured chirality of CMH.