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Scrutinizing the role of size reduction on the exchange bias and dynamic magnetic behavior in NiO nanoparticles

Abstract: NiO nanoparticles (NPs) with a nominal size range of 2–10 nm, synthesized via high-temperature pyrolysis of a nickel nitrate, have been extensively investigated using neutron diffraction and magnetic (ac and dc) measurements. The magnetic behavior of the NPs changes noticeably when their diameter decreases below 4 nm. For NPs larger than or equal to this size, Rietveld analysis of the room temperature neutron diffraction patterns reveals that there is a reduction in the expected magnetic moment per ion with respect to bulk NiO, which is linked to the existence of a magnetically disordered shell at the NP surface. The presence of two peaks in the temperature dependence of both the dc magnetization after zero-field-cooling and the real part of the ac magnetic susceptibility is explained in terms of a core (antiferromagnetic, AFM)/shell (spin glass, SG) morphology. The high-temperature peak (T>50 K) is associated with collective blocking of the uncompensated magnetic moments inside the AFM core. The low-temperature peak (T<10 K) is a signature of a SG-like freezing of the surface Ni2+ spins. In addition, an exchange bias (EB) effect emerges due to the core/shell magnetic coupling. The cooling field and temperature dependences of the EB effect and the coercive field are discussed in terms of the core size and the effective magnetic anisotropy of the NPs. However, NiO NPs of 2 nm in size no longer show AFM order and the Ni2+ magnetic moments freeze into a SG-like state below T - K, with no evidence of EB effect.

 Fuente: Nanotechnology, Vol. 26, Num. 30, Art. Num. 305705 (2015)

Editorial: IOP Publishing

 Año de publicación: 2015

Nº de páginas: 14

Tipo de publicación: Artículo de Revista

 DOI: 10.1088/0957-4484/26/30/305705

ISSN: 0957-4484,1361-6528

 Proyecto español: MAT2011-27573-C04 ; FC-15-GRUPIN14-037

Url de la publicación: https://doi.org/10.1088/0957-4484/26/30/305705

Autoría

RINALDI MONTES, NATALIA MAGDALENA

PEDRO GORRIA KORRES

MARTÍNEZ BLANCO, DAVID

FUERTES ARIAS, ANTONIO BENITO

PUENTE ORENCH, I.

JESUS ANGEL BLANCO RODRIGUEZ