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Ferromagnetic Resonance of NiCoFe2O4 Nanoparticles and Microwave Absorption Properties of Flexible NiCoFe2O4-Carbon Black/Poly(vinyl alcohol) Composites

Abstract

Effect of cationic disorder and particle morphology on ferromagnetic resonance (FMR) of NiCoFe2O4 nanoparticles (NPs) and electromagnetic shielding effectiveness of flexible composites (wherein nanoparticles are used as fillers) is presented. On annealing at 1000 ºC, spherical, ~25 nm, single crystalline (as-prepared) NPs transforms to octahedral, ~200 nm, polycrystalline (annealed) NPs and changes the cationic distribution significantly. Effect of shape, size and cationic distributions on the resonance properties is discussed using randomly-oriented anisotropic-axis model. Temperature dependent evolution of FMR spectra is found to be consistent with Bloch spin-relaxation model. Analysis of FMR spectra reveals that NiCoFe2O4 nanoparticles have large internal magnetic field along with broad FMR linewidths, ~2-3 kOe, signifying high magnetic losses essential for absorption of electromagnetic (EM) waves. Next, NiCoFe2O4-carbon black (NCF-CB) hybrids grafted in PVA matrix, as flexible composite films with a thickness of ~1.5 mm and are assessed for EM wave absorption properties over 8-18 GHz. As compared to annealed-NCF-CB/PVA (21 dB ~99.5%), as-prepared-NCF-CB/PVA exhibits significantly large SE of 27 dB (~99.9% attenuation of EM wave) composite film, with a dominant contribution from absorption (SEA~21dB). Electrical conductivity, electric modulus, and Cole-Cole plots reveal that dielectric losses in as-prepared-NCF-CB/PVA have significant contributions from cationic disorder and particle size, as compared to annealed-NCF-CB/PVA composites. Cationic disorder increases the d-d electron transition probability between adjacent ionic pairs such Co2+/Fe3+ and reduced particle size creates large interfacial polarization in as-prepared NCF/CB hybrids. Considerably large values of Landes g-factor, magnetic anisotropy and better impedance matching indicate dominant magnetic loss contribution in ap-NCF (g = 4.5) as compared to an-NCF (g = 2.5) at 300 K.

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Publication details

The article was received on 13 Jun 2017, accepted on 11 Jul 2017 and first published on 11 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP03953K
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Ferromagnetic Resonance of NiCoFe2O4 Nanoparticles and Microwave Absorption Properties of Flexible NiCoFe2O4-Carbon Black/Poly(vinyl alcohol) Composites

    G. Datt, C. Kotabage and A. C. Abhyankar, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP03953K

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