Metal/oxide composite films of Ni80Fe20/NixFe1-xO were prepared by dual ion beam reactive deposition.  The ion beam sputtered metal film is bombarded during growth with an oxygen ion flux from a secondary ion source.  The oxide phase forms by the shallow ion implantation of oxygen followed by supersaturation and precipitation.  The oxide is dispersed in the metal matrix as 10nm diameter crystallites.   Varying the oxygen ion flux can be used to control the oxide volume fraction.  The oxide has the rock salt structure but after vacuum annealing at 500C for 3 hours the spinel ferrite, NiFe2O4 is formed.  The metal/ferrite composites show unusually large anisotropic magnetoresistance (AMR) up to 4.5% at 298K and 14% at 77K as compared to about 1% in the metal/rock salt oxide mixtures.  The largest values are observed when the volume fraction of metal approaches the percolation limit.  The latter observation suggests that the enhanced anisotropic scattering is occurring at the metal/ferrite interface.  The AMR effect is caused by the spin-orbit interaction that gives rise to a field dependent scattering cross-section.  We suggest that in the metal/ferrite nanocomposites, strongly anisotropic scattering is associated with spin polarized oxygen p-orbitals in the ferrite that is exchange coupled to the ferromagnetic metal.  The p-orbitals have a larger scattering cross-section because they have a larger radial extent compared to the d-orbitals.  The oxygen p-orbitals only contribute to the AMR, however, when they are exchange coupled to the ferromagnetic conductor.
  Richard J. Gambino and Ko-Wei Lin Department of Materials Science and Engineering Stony Brook University Metal/oxide composite films of Ni80Fe20/NixFe1-xO were prepared by dual ion beam reactive deposition. The ion beam sputtered metal film is bombarded during growth with an oxygen ion flux from a secondary ion source. The oxide phase forms by the shallow ion implantation of oxygen followed by supersaturation and precipitation. The oxide is dispersed in the metal matrix as 10nm diameter crystallites. Varying the oxygen ion flux can be used to control the oxide volume fraction. The oxide has the rock salt structure but after vacuum annealing at 500C for 3 hours the spinel ferrite, NiFe2O4 is formed. The metal/ferrite composites show unusually large anisotropic magnetoresistance (AMR) up to 4.5% at 298K and 14% at 77K as compared to about 1% in the metal/rock salt oxide mixtures. The largest values are observed when the volume fraction of metal approaches the percolation limit. The latter observation suggests that the enhanced anisotropic scattering is occurring at the metal/ferrite interface. The AMR effect is caused by the spin-orbit interaction that gives rise to a field dependent scattering cross-section. We suggest that in the metal/ferrite nanocomposites, strongly anisotropic scattering is associated with spin polarized oxygen p-orbitals in the ferrite that is exchange coupled to the ferromagnetic metal. The p-orbitals have a larger scattering cross-section because they have a larger radial extent compared to the d-orbitals. The oxygen p-orbitals only contribute to the AMR, however, when they are exchange coupled to the ferromagnetic conductor.

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7/11/2002