Magnetic order in γ-Fe2O3 nanoparticles: a XMCD study

Spin-canting in spinel nanoparticles of maghemite has multiple origins, among which surface effects, finite-size effects or chemical disorder effects. XMCD at the Fe L2,3 edges allows to separate the contributions of the magnetic moments of Fe3+ ions in tetrahedral and octahedral sites of γ-Fe2O3. We investigate three powders of γ-Fe2O3 synthetized via aqueous precipitation: particles of average diameter 2.7, 8 nm and particles of average diameter 8 nm coated with phosphoric acid. The relative contributions of the spins of the Click to view the MathML source and the Click to view the MathML source ions are observed, varying the external magnetic field. Under high magnetic fields, a reduction of the magnetic contribution of the Click to view the MathML source ions occurs for 8 nm phosphate-coated particles by comparison with the uncoated ones. A similar reduction appears at lower magnetic fields for the small 2.7 nm particles