The exchange bias (EB) effect has been studied in Ni/NiO nanogranular samples obtained by annealing in H2, at different temperatures (200 £ Tann £ 300 °C), NiO powder previously ball-milled for 20 hours. Typically, the samples consist of Ni nanoparticles (mean size of 10-18 nm) embedded in a nanocrystalline NiO matrix. With increasing Tann, the Ni fraction varies from 4 % up to 69 %. The exchange field depends on the Ni amount, being maximum (~ 600 Oe), at T = 5 K, in the sample with 15 % Ni. In all the samples, the EB effect vanishes at T = 200 K. The structural features of the samples have been investigated by X-ray diffraction, electron microscopy and extended X-ray absorption fine structure and the low-temperature magneto-thermal behaviour has been thoroughly analyzed. The results show the existence of a structurally and magnetically disordered NiO component, which plays the key role in the EB mechanism.

Exchange bias and interface structure in the Ni/NiO nanogranular system

DEL BIANCO, LUCIA;BOSCHERINI, FEDERICO;
2008

Abstract

The exchange bias (EB) effect has been studied in Ni/NiO nanogranular samples obtained by annealing in H2, at different temperatures (200 £ Tann £ 300 °C), NiO powder previously ball-milled for 20 hours. Typically, the samples consist of Ni nanoparticles (mean size of 10-18 nm) embedded in a nanocrystalline NiO matrix. With increasing Tann, the Ni fraction varies from 4 % up to 69 %. The exchange field depends on the Ni amount, being maximum (~ 600 Oe), at T = 5 K, in the sample with 15 % Ni. In all the samples, the EB effect vanishes at T = 200 K. The structural features of the samples have been investigated by X-ray diffraction, electron microscopy and extended X-ray absorption fine structure and the low-temperature magneto-thermal behaviour has been thoroughly analyzed. The results show the existence of a structurally and magnetically disordered NiO component, which plays the key role in the EB mechanism.
L. Del Bianco; F. Boscherini; M. Tamisari; F. Spizzo; M. Vittori Antisari; E. Piscopiello
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/59690
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