Nanocomposites and nanomaterials 

Magnetostatic fields in multilayer composite films with bimodal granule size distribution
Shipkova I.G., Veretennikova Iu.I., Kholodov H.A.
Department of Physics of Metals and Semiconductors, National Technical University “Kharkiv Polytechnic Institute”. Kyrpychov St., 2, Kharkiv-61002, Ukraine. 
E-mail: ship@kpi.kharkov.ua

    Nanogranular magnetic systems show considerable promise for microwave electronics [1]. In particular, their resonance properties (ferromagnetic resonance fields, resonance linewidth) are of importance for electromagnetic wave absorbers. Since these properties are conditioned by inner magnetic fields, the problem of inner fields definition has been of interest of physicist-theorists as well as of developers of high-frequency electronic devices. In a number of cases the evaluation of dipolar fields for specific systems with parameters closed to real ones may be useful for comparison with an experiment. So, it was previously established [2] that the linewidth of ferromagnetic resonance in a multilayer system CoFeB)x-(SiO2)100-x /SiC increases sharply with decreasing concentration of magnetic granules to values ​​close to the percolation threshold. Our previous calculations for models with a regular and irregular distribution of particles in layers showed that such non-monotonic behavior cannot be explained only by the random arrangement of particles.We have calculated total in-plane projection of dipole magnetic fields for simple model of regular multilayer systems at low granule concentration (the distance between granules is about of granule diameter) after rearrangement and formation of complexes consisting of 5 particles. Granule concentration remains the same as before in the system of individual granules. Our calculations show that great difference of local values of dipole fields (up to 1500 Oe) exists at the point situated under individual particle and point situated under granule complex. It may explain large values of FMR linewidth for real samples at low magnetic phase concentration.

1.	Timonen J.V.I., Ras R.H.A., Ikkala O. et al. Magnetic nanocomposites at microwave frequencies // Trends in nanophysics: theory, experiment, technology, edited by V.Barsan and A.Aldea, Berlin: Springer-Verlag. – 2010. - P.257-285. 
2.	Iu.Chekrygina Iu., Devizenko A., Kalinin Y. et al.Magnetic and  Magneto-resonance Properties of Multilayered Systems Based on (CoFeB)x-(SiO2)100-x  Composite layers // Solid State Phenomena.-2014.- 215.- P.272-277.