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We present a study of the local magnetic properties of iron/iron oxide granular nanostructures by x-ray magnetic circular dichroism ͑XMCD͒. Metallic iron ͑␣-Fe͒ nanoparticles, with average sizes ranging from 5 to 13 nm, are embedded in a nanocrystalline oxide matrix composed of both magnetite ͑Fe 3 O 4 ͒ and maghemite ͑␥-Fe 2 O 3 ͒. These granular samples were synthesized by cold compacting core-shell nanoparticles, in which a 2 -3 nm-thick oxide layer surrounds the iron particles, synthesized by inert gas condensation. By exploiting the chemical selectivity and site sensitivity of XMCD, we were able to separate the magnetic contributions of the metallic core and of the two oxide phases present in the matrix and to study their behavior as a function of iron particle size and applied magnetic induction field. We detected the presence of a significant spin canting, predominantly affecting the octahedral sites of Fe in the oxide phase, and studied its dependence on the degree of structural disorder and applied magnetic induction field.

The surface electronic and magnetic properties of epitaxial La 2/3 Sr 1/3 MnO 3 / SrTiO 3 ͑001͒ films with extended bulk metallicity above the Curie temperature have been investigated. By angle-resolved photoemission we show that the surface electronic structure presents the e g dispersing band, responsible for the halfmetallicity, crossing the Fermi level and leading to a sharp Fermi edge. Quasiparticle excitations, reflecting the coherent polaronic ferromagnetic and metallic ground state, are clearly visible at the Fermi level and 16 K, while they disappear at room temperature, where a Fermi edge is still clearly visible. X-ray magnetic circular dichroism shows a robust subsurface magnetization up to T C , while spin-polarization Mott spectroscopy indicates a rapid suppression of the surface magnetization which disappears around room temperature. These results clearly demonstrate that a robust surface metallic electronic structure does not necessarily ensure the concomitant stabilization of long-range magnetic order.

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Despite its half-metallic character, La2∕3Sr1∕3MnO3 is currently not considered a good candidate for real spin electronic devices due to the dramatic deterioration of its spin polarization at room temperature. Using pulsed-laser deposition, we have grown thin films of La2∕3Sr1∕3MnO3, which display good room-temperature magnetic properties accompanied by a sizable increase of the temperature at which the metal-insulator transition takes place with respect to the Curie temperature. The persistence of the metallic character well above the Curie temperature indicates minor modifications of the electronic structure near the Fermi level, which is responsible for the half-metallicity. These films are good candidates for increasing the operating temperature of devices based on La2∕3Sr1∕3MnO3.

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