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ETUDE PAR RESONANCE MAGNETIQUE NUCLEAIRE DE L'ORDRE A COURTE DISTANCE DANS LE SYSTEME COBALT/FER :DE L'ALLIAGE MASSIF A LA MULTICOUCHE

Abstract : An NMR spectrum reflects the configuration environment probabilities around the probed nucleus, the technique is thus powerful for detailed analysis of the short range order and has been applied to the cobalt/iron system. Bulk alloys, thin film alloys and multilayers studies are presented in this work. Detailed bulk sample analysis allowed refinement of the short range order knowledge in bulk alloys using Monte Carlo simulations. Thin film alloys study shows that the body cubic centred (bcc) concentration limit is shifted up to 90% cobalt, whereas in bulk alloys, the face cubic centred phase appears above 75%. New ordered structures are also observed. These phases, theoretically predicted, are also visible in metal-spinel composites made at low temperature by soft chemical methods. These ordered phases could be reproduced using Monte Carlo simulations. This particular short range order is connected to the preparation methods and to the low deposition temperature : atoms can find their most favourable position according to surface energies criteria. Multilayers analysis have shown that 20 Å is the limit thickness for metastable bcc cobalt. However, only 6 Å build up continuous pure cobalt planes, 5 Å are clustered in mixed planes and the rest is contained in a rather homogeneous Co75%Fe25% bcc alloy. One main conclusion of this study is that the stabilisation extension of the bcc phase beyond the 75% limit which corresponds in bulk alloys to the appearance of the face cubic centred phase, is realised through the mixture of bcc Co75%Fe25% alloy and pure bcc cobalt. This 75% concentration seems a common limit for the cobalt iron system in the bcc phase.
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Contributor : Jean-Philippe Jay <>
Submitted on : Wednesday, September 24, 2003 - 3:29:41 PM
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Jean-Philippe Jay. ETUDE PAR RESONANCE MAGNETIQUE NUCLEAIRE DE L'ORDRE A COURTE DISTANCE DANS LE SYSTEME COBALT/FER :DE L'ALLIAGE MASSIF A LA MULTICOUCHE. Matière Condensée [cond-mat]. Université Louis Pasteur - Strasbourg I, 1995. Français. ⟨tel-00003414⟩

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