Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles

Disorder among surface spins is a dominant factor in the magnetic response of magnetic nanoparticle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8 ± 0.5 nm outer diameter and enhanced surface-to-volume rat...

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Bibliographic Details
Published in:Scientific reports 2015-10, Vol.5 (1), p.15054, Article 15054
Main Authors: Khurshid, Hafsa, Lampen-Kelley, Paula, Iglesias, Òscar, Alonso, Javier, Phan, Manh-Huong, Sun, Cheng-Jun, Saboungi, Marie-Louise, Srikanth, Hariharan
Format: Article
Language:English
Subjects:
639/766/119
639/766/119/997
Exchange bias
Hollow nanoparticles
Humanities and Social Sciences
Monte Carlo method
multidisciplinary
Mètode de Montecarlo
Nanoparticles
Nanopartícules
Physics
PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Science
Spin glass
Spin glasses
Surface spins
Vidres de spin
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Summary:Disorder among surface spins is a dominant factor in the magnetic response of magnetic nanoparticle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8 ± 0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K and become frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins. Monte Carlo simulations of a hollow particle corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures.
ISSN:2045-2322
2045-2322
DOI:10.1038/srep15054