Modeling of magnetic nanoparticles:
We work on the modelling of magnetic nanoparticles in two approaches:
(a) Individual nanoparticles as multispin systems. Our recent results include modelling of magnetic nanoparticles of different shapes and internal structures with Neel surface anisotropy [1,2]. Our approach is based on the Lagrange multiplier technique [1,2] and recently developed constrained Monte Carlo to include temperature fluctuations [3].
We also work on the modelling of core-shell nanoparticles, including the exchange-bias phenomenon. Recently, we have suggested the use of these nanoparticles for «beating the superparamagnetic limit· in magnetic recording within the heat-assisted scheme [4].
(b) Ensemble of nanoparticles. We work on the understanding of magnetostatic and exchange interactions in an e of magnetic nanoparticles. Our approach involves energy barrier calculations in a multi-dimensional space and the kinetic Monte Carlo dynamics [5]. In this line we closely collaborate with experimental groups working on biological applications of magnetic nanoparticles such as NMR [6]
Blocking temperature (normalized to the non-interacting ensemble case) as a function of surface packing densities for maghemite nanoparticles embedded on a capsule with D=200 nm.
References:
[1] R.Yanes, O.Chubykalo-Fesenko, H.Kachkachi D.Garanin,R.Evans and R.W.Chantrell «Effective anisotropies and energy barriers in magnetic nanoparticles with Neel surface anisotropy.», Phys Rev B 76 (2007) 064416.
[2] R. Yanes and O. Chubykalo-Fesenko “Modelling of the influence of the Néel surface anisotropy on the enhancement of the magnetic anisotropy in Co nanoparticle.”, J.Phys. D 42 (2009) 055013.
[3] R.Yanes, O.Chubykalo-Fesenko, R.F.L.Evans and R.W.Chantrell “Temperature dependence of the effective anisotropies in magnetic nanoparticles with Neel surface anisotropy”, J.Phys. D: Appl. Phys. 43 (2010) 0.
[4] R. F.L. Evans, R. Yanes, O.Mryasov, R.W.Chantrell and O.Chubykalo-Fesenko “On beating the superparamagnetic limit with exchange bias”, Europhys. Lett. 88 (2009) 57004.
[5] K.Yu.Guslienko, T.J.Klemmer, X.W.Wu, R.W.Chatnrell, D.Weller and O.Chubykalo «Computational and experimental study of exchange coupling in FePt self-organised magnetic arrays» Physica B 372, (2006) 328-331
[6] A. Abbasi, L.Gutierrez, L. del Mercato, F.Herrantz, O.Chubykalo-Fesenko, S.Ventemillas-Verdaguer, W.Parak, M.P.Morales, J.M.Gonzalez, A.Hernando, P. de la Presa «Magnetic nanocapsules for NMR imaging: effect of magnetic nanoparticle spatial distribution and aggregation», J. Phys. Chem. C 115 (2011) 6257.