Abstract
Hard L10-ordered FePd ultra-thin films were epitaxially grown by means of a molecular beam epitaxy system on MgO-(100) monocrystalline substrates. Because of the very low thickness of the films, small amounts of superparamagnetic L10-FePd particles were also formed on the surface. The magnetic properties of the films are typical of highly coercive systems showing a strong perpendicular anisotropy. These hard films were used for the development of soft/hard exchange-spring magnets, by depositing different thickness of iron. Fe reacts with the surface FePd small particles giving rise to a Fe(Pd) compound with a broad distribution of particle sizes. The resulting systems are bi-layers constituted by a soft Fe(Pd) and a hard L10-FePd layer intercalated by a very thin region of small particles. For soft/hard thickness ratio nominally equal to 1 the magnetic behaviour is typical of a single-phase hard magnet. By increasing the nominal thickness ratio up to 3, the behaviour becomes typical of an exchange-coupled magnet with hysteresis loops characterized by two critical fields.
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