Magnetoresistance of nanogranular Ni/NiO controlled by exchange anisotropy

• Published in: Journal of magnetism and magnetic materials Vol. 339; pp. 94 - 99
• Main Authors: Del Bianco, L., Spizzo, F., Tamisari, M., Allia, P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.2013; Elsevier
• Subjects: Anisotropy; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Exchange anisotropy; Exchange bias effect; Giant magnetoresistance; Magnetic properties and materials; Magnetic properties of nanostructures; Magnetization; Magnetoresistance; Magnetoresistivity; Magnetotransport phenomena, materials for magnetotransport; Nanocrystals; Nanogranular material; Nanostructure; Nickel; Physics; Reduction; Nanogranular material; Giant magnetoresistance; Exchange anisotropy; Exchange bias effect; Metallic conduction; Magnetization; Nanocomposites; Remanent magnetization; Anisotropy; Nickel; Exchange interactions; Nanocrystal; Nickel oxide
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2013.03.012

A link between exchange anisotropy and magnetoresistance has been found to occur in a Ni/NiO sample consisting of Ni nanocrystallites (mean size ∼13nm, Ni content ∼33vol%) dispersed in a NiO matrix. This material shows metallic-type electric conduction and isotropic spin-dependent magnetoresistance as well as exchange bias effect. The latter is the outcome of an exchange anisotropy arising from the contact interaction between the Ni phase and the NiO matrix. Combined analysis of magnetization M(H) and magnetoresistance MR(H) loops measured in the 5–250K temperature range after zero-field-cooling (ZFC) and after field-cooling (FC) from 300K reveals that the magnetoresistance is influenced by exchange anisotropy, which is triggered by the FC process and can be modified in strength by varying the temperature. Compared to the ZFC case, the exchange anisotropy produces a horizontal shift of the FC MR(H) loop along with a reduction of the MR response associated to the reorientation of the Ni moments. A strict connection between magnetoresistance and remanent magnetization of FC loops on one side and the exchange field on the other, ruled by exchange anisotropy, is indicated. •Nanogranular Ni/NiO with giant magnetoresistance (MR) and exchange bias effect.•Exchange anisotropy produces a shift of the field-cooled MR(H) loop and reduces MR.•MR, remanence of field-cooled loops and exchange field are three correlated quantities.•It is possible to control MR of nanogranular systems through the exchange anisotropy.