156
H. Khurshid et al.
us finely tune the morphology of hollow MNPs by controlling different reaction
parameters, such as annealing temperature and/or surfactant concentration. We have
also described in detail how iron-oxide-based hollow MNPs can be obtained from
the evolution of an original core/shell nanoparticle, first into a core/void/shell, and
then into a hollow morphology (i.e., Kirkendall effect). The shell in these hollow
MNPs is typically composed of small randomly oriented nanograins that play a
crucial role in the magnetic response of these nanoparticles. The static and dynamic
magnetic properties of hollow MNPs are radically different from those observed in
their solid counterparts. The high number of surface spins present, together with the
nanogranular nature of the shell, gives rise to high magnetic frustration and spin
glass like behaviors. As a result, surface anisotropy is greatly enhanced, leading
often to the appearance of a prominent exchange bias effect. In particular, we have
described how this EB phenomenon depends on the thickness of the shell, by carefully
analyzing the evolution of EB as a function of the morphology, from core/shell to
hollow. We have shown that a minimum shell thickness is crucial in enabling the
presence of additional interfaces (i.e., reversible and irreversible spins) that enhances
the EB effect. These experimental studies have been complemented with Monte
Carlo simulations. Atomistic simulations confirm the presence of strongly disordered
surface layers in the hollow particle morphology, with complex energy landscapes
that underlie both glass-like dynamics and magnetic irreversibility. Finally, potential
applications of the hollow MNPs have been reviewed, especially in the fields of
biomedicine, catalysis, batteries, sensing, and data storage.
With the continuous improvement in synthesis techniques and the development of
novel and facile synthesis routes, it is anticipated that we will attain a better control
over the morphology and other characteristics of hollow MNPs. This will allow us
to overcome several of the main limitations currently associated with these systems,
such as reduced magnetic response, non-uniform hollow structure, instability of
the hollow morphology, limited encapsulation/release efficiency, and reduced EB
effect at room temperature. We foresee that the progressive work on this field will
eventually lead toward multifunctional hollow MNPs with enhanced properties and
novel applications.
References
1. K. Cheng, S. Peng, C. Xu, S. Sun, J. Am. Chem. Soc. 131, 10637 (2009)
2. K. Cheng, N.A. Frey, S. Sun, S. Peng, K. Cheng, S. Sun, Chem. Soc. Rev. 38, 2532 (2009)
3. G.A.O. Jinhao, G.U. Hongwei, X.U. Bing, Acc. Chem. Res. 42, 1097 (2009)
4. A.H. Lu, E.L. Salabas, F. Schüth, Angew. Chemie. Int. Ed. 46, 1222 (2007)
5. D. Weller, A. Moser, IEEE Trans. Magn. 35, 4423 (1999)
6. R.D. Desautels, E. Skoropata, Y.-Y. Chen, H. Ouyang, J.W. Freeland, J. van Lierop, Appl. Phys.
Lett. 99, 262501 (2011)
7. M. Knobel, W.C. Nunes, L.M. Socolovsky, E. De Biasi, J.M. Vargas, J.C. Denardin, (n.d.)
8. B.D. Terris, T. Thomson, J. Phys. D. Appl. Phys. 38, R199 (2005)
9. T. Neuberger, B. Schöpf, H. Hofmann, M. Hofmann, B. Von Rechenberg, in J. Magn. Magn.
Mater. (2005), pp. 483–496
H. Khurshid et al.
us finely tune the morphology of hollow MNPs by controlling different reaction
parameters, such as annealing temperature and/or surfactant concentration. We have
also described in detail how iron-oxide-based hollow MNPs can be obtained from
the evolution of an original core/shell nanoparticle, first into a core/void/shell, and
then into a hollow morphology (i.e., Kirkendall effect). The shell in these hollow
MNPs is typically composed of small randomly oriented nanograins that play a
crucial role in the magnetic response of these nanoparticles. The static and dynamic
magnetic properties of hollow MNPs are radically different from those observed in
their solid counterparts. The high number of surface spins present, together with the
nanogranular nature of the shell, gives rise to high magnetic frustration and spin
glass like behaviors. As a result, surface anisotropy is greatly enhanced, leading
often to the appearance of a prominent exchange bias effect. In particular, we have
described how this EB phenomenon depends on the thickness of the shell, by carefully
analyzing the evolution of EB as a function of the morphology, from core/shell to
hollow. We have shown that a minimum shell thickness is crucial in enabling the
presence of additional interfaces (i.e., reversible and irreversible spins) that enhances
the EB effect. These experimental studies have been complemented with Monte
Carlo simulations. Atomistic simulations confirm the presence of strongly disordered
surface layers in the hollow particle morphology, with complex energy landscapes
that underlie both glass-like dynamics and magnetic irreversibility. Finally, potential
applications of the hollow MNPs have been reviewed, especially in the fields of
biomedicine, catalysis, batteries, sensing, and data storage.
With the continuous improvement in synthesis techniques and the development of
novel and facile synthesis routes, it is anticipated that we will attain a better control
over the morphology and other characteristics of hollow MNPs. This will allow us
to overcome several of the main limitations currently associated with these systems,
such as reduced magnetic response, non-uniform hollow structure, instability of
the hollow morphology, limited encapsulation/release efficiency, and reduced EB
effect at room temperature. We foresee that the progressive work on this field will
eventually lead toward multifunctional hollow MNPs with enhanced properties and
novel applications.
References
1. K. Cheng, S. Peng, C. Xu, S. Sun, J. Am. Chem. Soc. 131, 10637 (2009)
2. K. Cheng, N.A. Frey, S. Sun, S. Peng, K. Cheng, S. Sun, Chem. Soc. Rev. 38, 2532 (2009)
3. G.A.O. Jinhao, G.U. Hongwei, X.U. Bing, Acc. Chem. Res. 42, 1097 (2009)
4. A.H. Lu, E.L. Salabas, F. Schüth, Angew. Chemie. Int. Ed. 46, 1222 (2007)
5. D. Weller, A. Moser, IEEE Trans. Magn. 35, 4423 (1999)
6. R.D. Desautels, E. Skoropata, Y.-Y. Chen, H. Ouyang, J.W. Freeland, J. van Lierop, Appl. Phys.
Lett. 99, 262501 (2011)
7. M. Knobel, W.C. Nunes, L.M. Socolovsky, E. De Biasi, J.M. Vargas, J.C. Denardin, (n.d.)
8. B.D. Terris, T. Thomson, J. Phys. D. Appl. Phys. 38, R199 (2005)
9. T. Neuberger, B. Schöpf, H. Hofmann, M. Hofmann, B. Von Rechenberg, in J. Magn. Magn.
Mater. (2005), pp. 483–496