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Theses

Development and integration of oxide spinel thin films into heterostructures for spintronics

Abstract : Thin spinel oxide films of NiFe2O4 and CoCr2O4 were grown by RF sputtering on different oxide substrates to study the magnetic and electric properties with the aim of integrating them into heterostructures for spintronics devices.
It is found that epitaxial growth allows stabilization of novel spinel NiFe2O4 phases that do not exist in its bulk form with properties, such as an enhancement of the magnetic moment or the ability to tune its electrical properties changing from insulating, as in bulk, to conductive. We argue that the enhanced moment results from a partial cation inversion of the NiFe2O4, in which Ni2+ ions are distributed among the two available sites of the spinel structure. Oxygen vacancies are likely to promote the metallic behavior by inducing mixed-valence Fe2+/3+ states at the octahedral sites.
The conductive NiFe2O4 films were used as ferrimagnetic electrodes in a magnetic tunnel junction. A substantial tunnel magnetoresistance has been measured with values corresponding to a spin polarization of NiFe2O4 of about 40%, essentially constant up to 280K. The insulating NiFe2O4 was successfully implemented as a ferrimagnetic tunnel barrier into a spin filter device and is thus the first spin filter realized with a complex oxide barrier. A filtering effect has been signaled by a tunnel magnetoresistance.
For the CoCr2O4 films grown on MgO(001) and MgAl2O4(001) it was found that this oxide has a definite tendency to display a three-dimensional growth. with well defined, fully faceted, pyramidal objects. We have shown that fully faceted templates can be obtained and perspectives for further applications are discussed.
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https://tel.archives-ouvertes.fr/tel-00011342
Contributor : Ulrike Luders <>
Submitted on : Tuesday, January 10, 2006 - 6:44:27 PM
Last modification on : Friday, January 10, 2020 - 9:08:57 PM
Long-term archiving on: : Saturday, April 3, 2010 - 7:15:16 PM

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  • HAL Id : tel-00011342, version 1

Citation

Ulrike Luders. Development and integration of oxide spinel thin films into heterostructures for spintronics. Condensed Matter [cond-mat]. INSA de Toulouse; Universitat Autónoma de Barcelona, 2005. English. ⟨tel-00011342⟩

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