FMR and DSC study of maghemite nanoparticles in PMMA polymer matrix J. Typek 1, N. Guskos 1,2, A. Szymczyk 1, D. Petridis 3 1 Institute of Physics, Szczecin University of Technology, Szczecin, Poland 2 Department of Physics, University of Athens, Greece 3 NCSR Demokritos, Aghia Paraskevi, Athens, Greece

Maghemite – γ-Fe 2 O 3 (iron(III) oxide) inverse spinel cubic structure stoichiometric formula (Fe 3+ ) A O 2- (Fe 3+ Fe 3+ 2/3 [ ] 1/3 ) B O Fe 3+ ions located in tetrahedral sites (A-sites) and 16 Fe 3+ ions in octahedral sites (B-sites) collinear ferrimagnet antiparallel magnetic sublattices A (4.18 μ B ) and B (4.41 μ B ) T C = ºC

PMMA (polymethyl methacrylate) Polymethyl methacrylate (PMMA) or poly (methyl 2-methylpropenoate) is the synthetic polymer of methyl methacrylate. This thermoplastic and transparent plastic is sold by the tradenames Plexiglas, R-Cast, Perspex, Plazcryl, Limacryl, Acrylex, Acrylite, Acrylplast, Altuglas, Polycast and Lucite and is commonly called acrylic glass or simply acrylic. The material was developed in 1928 in various laboratories and was brought to market in Temperature of the glass transition T g = ºC Melting temperatures ºC

Synthesis of γ-Fe 2 O 3 /PMMA nanocomposite Procedure: preparation of capped magnetic nanoparticles → exchange of the oleate units by methacrylate units → preparation of γ-Fe 2 O 3 /PMMA composite γ-Fe 2 O 3 nanocrystalline particles with an average size of 10 nm, chemically bonded to the chains The surface bond oleate groups can be fully exchanged with metacrylate units by refluxing in ethanol. The exchange reaction ensures the chemical bonding of methacrylate units to the surface of nanoparticles, which in turn, undergo the polymerization with the vinyl groups of the methyl mathacrylate. Magnetic nanoparticles capped with oleic acid were prepared by one step method involving partial oxidation of Fe(II) in alkaline solutions by dilute H 2 O 2. The reaction was conducted in the presence of oleic acid and under biphase conditions. Incorporation of nanoparticles in the polymer matrix through chemical bonding FMR investigated samples – 5 wt% and 10 wt% γ-Fe 2 O 3

DSC study of γ-Fe 2 O 3 /PMMA nanocomposite Maghemite content wt% T g [ºC] C p [J/g ºC] T g increases with maghemite content increase →reduced dynamics of polymer chains, hidering segmental motion c p heat capacity decreases with maghemite content → increase of steric hindrance

FMR spectra – temperature dependence 5 wt% High-temperature rangeLow-temperature range T block ~ 40 K ? T=150 K PMMA relaxation?

FMR parameters – integrated intensity 5 wt% FMR integrated intensity I z ~ (FMR signal amplitude)·(ΔB) 2 Integrated intensity I z ~ spin susceptibility χ’’ I z ·T ~(magnetic moment) 1/2

FMR spectra: γ-Fe 2 O 3 content 10 wt% 5 wt% The difference (in intensity) is observed for T>250 K. It could be attributed to the dipol- dipol magnetic interaction between nanoparticles.

FMR spectra - decomposition T=71 K, 5 wt% Narrow (high-field) component → magnetic easy axis  external magnetic field Broad (low-field) component → magnetic easy axis || external magnetic field

FMR spectrum decomposition 5 wt%

FMR spectrum decomposition g-factor Linewidth [Gs] Temperature [K] Narrow component Broad component Magnetic moment 10 wt%

FMR spectrum decomposition Integrated intensity [arb. units] Temperature [K] Narrow component (high field) Broad component (low-field) 10 wt% B0B0 B0B0

Conclusions Increase in maghemite content → T glass decreases Blocking temperature ~40 K Relaxation in PMMA=150 K Maghemite content differences seen in FMR above 250 K FMR spectrum reflects magnetic anisotropy of nanoparticles