title: Local spin dynamics of iron oxide magnetic nanoparticles dispersed in different solvents with variable size and shape: A1H NMR study.
abstract: Colloidal magnetic nanoparticles (MNPs) based on a nearly monodisperse iron oxide core and capped by oleic acid have been used as model systems for investigating the superparamagnetic spin dynamics by means of magnetometry measurements and nuclear magnetic resonance (1H NMR) relaxometry. The key magnetic properties (saturation magnetization, coercive field, and frequency dependent "blocking" temperature) of MNPs with different core size (3.5 nm, 8.5 nm, and 17.5 nm), shape (spherical and cubic), and dispersant (hexane and water-based formulation) have been determined.1H NMR dispersion profiles obtained by measuring the r1(longitudinal) and r2(transverse) nuclear relaxivities in the frequency range 0.01-60 MHz confirmed that in all samples the physical mechanisms that drive the nuclear relaxation are the Néel reversal at low temperature and the Curie relaxation at high frequency. The magnetization reversal time at room temperature extracted from the fitting of NMR data falls in the typical range of superparamagnetic systems (10-9-10-10s). Furthermore, from the distance of minimum approach we could conclude that water molecules do not arrive in close vicinity of the magnetic core. Our findings contribute to elucidate the local spin dynamics mechanisms in colloidal superparamagnetic nanoparticles which are useful in biomedical application as, e.g., contrast agents for magnetic resonance imaging.
authors.affiliation: Dipartimento di Fisica and INSTM, Università degli Studi di Milano, Milano, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Basini
authors.affiliation: EPR Research Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: T
authors.identifier: 0000000172612119
authors.initials: T
authors.lastname: Orlando
authors.affiliation: Dipartimento di Fisica and INSTM, Università degli Studi di Milano, Milano, Italy.
authors.forename: P
authors.identifier: 0000000323880402
authors.initials: P
authors.lastname: Arosio
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche and INSTM, Università di Cagliari, Monserrato, Italy.
authors.forename: M F
authors.initials: MF
authors.lastname: Casula
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche and INSTM, Università di Cagliari, Monserrato, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Espa
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche and INSTM, Università di Cagliari, Monserrato, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Murgia
authors.affiliation: ICCOM-CNR and INSTM, Sesto Fiorentino, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Sangregorio
authors.affiliation: Dipartimento di Chimica and INSTM, Università degli studi di Firenze, Sesto Fiorentino, Italy.
authors.forename: C
authors.identifier: 0000000337054283
authors.initials: C
authors.lastname: Innocenti
authors.affiliation: Dipartimento di Fisica and INSTM, Università degli Studi di Milano, Milano, Italy.
authors.forename: A
authors.identifier: 0000000216870436
authors.initials: A
authors.lastname: Lascialfari