Abstracts Book - IMRC 2018

• SF1-O010
SIMULATION AND MODELLING OF GRAIN BOUNDARY
ANISOTROPY IN NANO-POLYCRYSTALLINE MAGNETIC THIN FILMS
Jose Dario Agudelo Giraldo 1,2 , Elisabeth Restrepo Parra 2
1 Universidad Autónoma de Manizales, Caldas, Colombia. 2 Universidad Nacional de Colombia, ,
Colombia.
A complete model for studying the magnetic behavior of polycrystalline thin
films at nano-scale is presented. Grain boundaries are regions characterized by
a high degree of local structural disorder and big values of local anisotropies are
expected. This model includes terms as exchange interaction, dipolar
interaction, external field and various types of anisotropies. The RKKY
approximation was implemented for exchange interaction at different distance,
mainly in grain boundaries according to different reports obtained by mean ab
initio calculations. Anisotropy term includes crystalline, surface and boundary
anisotropies. The temperature dependence of the anisotropy and quantification
of local structural disorder were considered. Particularly, a special attention is
paid to the disorder vector what determines the loss of cubic symmetry in the
crystalline structure. In the case of the dipolar interaction, a similar
implementation of the fast multiple method (FMM) was performed. The
investigation of the effect of the grain boundary anisotropy was addressed by
mean a standard Monte Carlo simulation in the framework of classical
Heisenberg spin model. Results revealed that i) by keeping the same number of
grains, different realizations give rise to different spontaneous magnetizations,
ii) the critical exponent of the magnetization is different that of pure models.
The difference is attributed to the complexity of the lattice structure and
consistent with a distribution of critical temperatures, iii) the way in which the
boundary anisotropy varies with temperature and its strength are determinant
factors for blocking temperatures. The respective hysteretic properties are
presented and discussed.
Keywords: nanogranular thin films, magnetic behavior, Grain boundary anisotropy
Presenting authors email: jdagudelog@unal.edu.co