Ovejero J.G., Cabrera D., Carrey J., Valdivielso T., Salas G., Teran F.J. and 'This work has been partially supported by the European Commission (MULTIFUN, no. 262943), Spanish Ministry of Economy and Competitiveness (MAT2013-47395-C4-3-R), and Madrid Regional Government (NANOFRONTMAG, S2013/MIT-2850). F. J. T acknowledges financial support from the Ram?n y Cajal subprogram (RYC-2011-09617). J. C. and F. J. T. thank the European Cost Action TD1402 (RADIOMAG). J. C. thanks support by the ITMO Cancer during the 'Plan cancer 2009-2013'. Numerical simulations were performed using HPC resources from CALMIP (Grant 2014-P1405). We thank Dr Daniel Ortega for careful reading of the manuscript and Dr Mar?a del Puerto Morales for fruitful discussions and her interest in this work.'