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 (2008). Exchange bias and interface structure in the Ni/NiO nanogranular system. JOURNAL OF PHYSICS. D, APPLIED PHYSICS, 41, 134008-134008-7 [10.1088/0022-3727/41/13/134008].
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
