Chapter 1
Single Nanomagnet Behaviour:
Surface and Finite-Size Effects
Òscar Iglesias and Hamid Kachkachi
Abstract In this chapter we discuss some intrinsic features of nano-scaled magnetic systems, such as finite-size, boundary, shape and surface effects. We mainly
review in a succinct manner the main results of previous works. We first present the
basics of theoretical models and computational techniques and their applications to
individual nanomagnets. Results of both simulations and analytic calculations for
specific materials, compositions and shapes are given based on these models.
1.1 Introduction
Nanomagnetism is the magnetism of nano-scaled objects. In general, the magnetic
state of a body is characterized by its macroscopic property that is magnetization,
which is the module of the statistical average of the magnetic moment vector, projected onto the applied field. The module and orientation of the latter are stable with
respect to thermal fluctuations during a certain interval of time that depends on the
underlying material, the size and shape of the magnetic body, as well as external
environment parameters such as temperature and magnetic fields. Depending on the
system’s setup, the magnetic moment may adopt several possible orientations corresponding to the various minima of its energy, which are separated from each other
by energy barriers that depend in turn on various intrinsic physical parameters of the
system as well as on external ones. In bulk systems the energy barriers happen to be
too high for the system to cross them (within the observation time) and to spontaneously switch from one state to another. On the opposite, in nano-scaled systems
these barriers are drastically reduced leading to rather short switching times. Indeed,
when the size of the system reduces from bulk to nanometric scales, the magnetic
Ò. Iglesias (B)
UB and IN2UB, Barcelona, Spain
e-mail: oscariglesias@ub.edu
H. Kachkachi
UPVD and PROMES CNRS UPR8521, Perpignan, France
e-mail: hamid.kachkachi@promes.cnrs.fr
© Springer Nature Switzerland AG 2021
D. Peddis et al. (eds.), New Trends in Nanoparticle Magnetism,
Springer Series in Materials Science 308,
https://doi.org/10.1007/978-3-030-60473-8_1
3
Single Nanomagnet Behaviour:
Surface and Finite-Size Effects
Òscar Iglesias and Hamid Kachkachi
Abstract In this chapter we discuss some intrinsic features of nano-scaled magnetic systems, such as finite-size, boundary, shape and surface effects. We mainly
review in a succinct manner the main results of previous works. We first present the
basics of theoretical models and computational techniques and their applications to
individual nanomagnets. Results of both simulations and analytic calculations for
specific materials, compositions and shapes are given based on these models.
1.1 Introduction
Nanomagnetism is the magnetism of nano-scaled objects. In general, the magnetic
state of a body is characterized by its macroscopic property that is magnetization,
which is the module of the statistical average of the magnetic moment vector, projected onto the applied field. The module and orientation of the latter are stable with
respect to thermal fluctuations during a certain interval of time that depends on the
underlying material, the size and shape of the magnetic body, as well as external
environment parameters such as temperature and magnetic fields. Depending on the
system’s setup, the magnetic moment may adopt several possible orientations corresponding to the various minima of its energy, which are separated from each other
by energy barriers that depend in turn on various intrinsic physical parameters of the
system as well as on external ones. In bulk systems the energy barriers happen to be
too high for the system to cross them (within the observation time) and to spontaneously switch from one state to another. On the opposite, in nano-scaled systems
these barriers are drastically reduced leading to rather short switching times. Indeed,
when the size of the system reduces from bulk to nanometric scales, the magnetic
Ò. Iglesias (B)
UB and IN2UB, Barcelona, Spain
e-mail: oscariglesias@ub.edu
H. Kachkachi
UPVD and PROMES CNRS UPR8521, Perpignan, France
e-mail: hamid.kachkachi@promes.cnrs.fr
© Springer Nature Switzerland AG 2021
D. Peddis et al. (eds.), New Trends in Nanoparticle Magnetism,
Springer Series in Materials Science 308,
https://doi.org/10.1007/978-3-030-60473-8_1
3