title: Evolution of the magnetic structure with chemical composition in spinel iron oxide nanoparticles.
abstract: Magnetic properties of iron oxide nanoparticles with spinel structure are strictly related to a complex interplay between cationic distribution and the presence of a non-collinear spin structure (spin canting). With the aim to gain better insight into the effect of the magnetic structure on magnetic properties, in this paper we investigated a family of small crystalline ferrite nanoparticles of the formula CoxNi1-xFe2O4 (0 ≤x≤ 1) having equal size (≈4.5 nm) and spherical-like shape. The field dependence of magnetization at low temperatures indicated a clear increase of magnetocrystalline anisotropy and saturation magnetization (higher than the bulk value for CoFe2O4: ∼130 A m(2) kg(-1)) with the increase of cobalt content. The magnetic structure of nanoparticles has been investigated by Mössbauer spectroscopy under an intense magnetic field (8 T) at a low temperature (10 K). The magnetic properties have been explained in terms of an evolution of the magnetic structure with the increase of cobalt content. In addition a direct correlation between cationic distribution and spin canting has been proposed, explaining the presence of a noncollinear spin structure in terms of superexchange interaction energy produced by the average cationic distribution and vacancies in the spinel structure.
authors.affiliation: Dipartimento di Fisica, Università di Cagliari, S.P. Monserrato-Sestu km 0.700, 09042, Monserrato, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Muscas
authors.forename: N
authors.initials: N
authors.lastname: Yaacoub
authors.forename: G
authors.initials: G
authors.lastname: Concas
authors.forename: F
authors.initials: F
authors.lastname: Sayed
authors.forename: R
authors.initials: R
authors.lastname: Sayed Hassan
authors.forename: J M
authors.initials: JM
authors.lastname: Greneche
authors.forename: C
authors.initials: C
authors.lastname: Cannas
authors.forename: A
authors.initials: A
authors.lastname: Musinu
authors.forename: V
authors.initials: V
authors.lastname: Foglietti
authors.forename: S
authors.initials: S
authors.lastname: Casciardi
authors.forename: C
authors.initials: C
authors.lastname: Sangregorio
authors.forename: D
authors.initials: D
authors.lastname: Peddis