Nonzero orbital moment in high coercivity ε-Fe<inf>2</inf>O <inf>3</inf> and low-temperature collapse of the magnetocrystalline anisotropy

The magnetic properties of ε-Fe2O3 nanoparticles are investigated by x-ray magnetic circular dichroism. Sum rules relating the orbital and spin moment in the Fe 3d band to the Fe L2,3 absorption cross sections show that the Fe orbital moment (morb) is considerably high, explaining the origin of the large coercivity of this material at room temperature. Moreover, at T∼110 K, the collapse of the coercivity (H c) and the magnetocrystalline anisotropy coincides with a strong reduction of the spin-orbit coupling evidenced by a drastic drop of m orb. The decrease in morb originates from changes in the electron transfer between Fe and O ions accompanied by significant modifications of some of the Fe-O bond distances. Similarly, the recovery of morb at lower temperatures mimics the behavior of the Fe-O bond lengths. © 2009 The American Physical Society.