The epsilon phase of Fe$_2$O$_3$ (ε-Fe$_2$O$_3$) presents captivating properties and it is receiving extraordinary attention due to its great application potentials. It stands out for its huge coercive field (up to 2 T at room temperature), millimeter-wave ferromagnetic resonance, remarkable non-linear magneto-optical effect, magneto-electric coupling , and room temperature ferroelectricity . It has been much less studied than other iron (III) oxides because its formation requires special conditions .
ε-Fe$_2$O$_3$ presents a complex noncentrosymmetric structure (Pna2$_1$) with three distinct octahedral and one tetrahedral environments for Fe sites. We present a neutron-based investigation on the rich magnetic phase diagram and properties of geometrically frustrated ε-Fe$_2$O$_3$ nanoparticles. The nature of the incommensurate magnetic order, attributed by some authors to a spiral ground state , was investigated in zero and applied magnetic fields, and reinterpreted in the light of the models confronted to neutron data . The study illustrates the interplay between the huge magnetic anisotropy, frustration and the stabilization of the super-hard ferrimagnetic phase in the 150-500 K interval.
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