Abstract
A comparative study at the ambient temperature of the ferromagnetic resonance (FMR) spectra of Ni/ZnO andNi/γ-Fe2O3nanocomposites (NCs) is reported. A microstrip transmission line technique was used to measure the FMR profiles and linewidths in the 8–24 GHz frequency range. The samples were placed at the center of a microstrip line where the derivative of the absorbed power was measured using a standard ac field modulation technique (10 Oe amplitude) and lock-in detection. The analysis of the FMR spectra can be interpreted as arising from aggregates of magnetic nanoparticles, each of which resonates in an effective magnetic field composed of the applied field, the average (magnetostatic) dipolar field, and the randomly oriented magnetic anisotropy field. It is found that frequency and applied magnetic field strongly influence the lineshape of the FMR spectra. Two observations are identified within the FMR spectra. On the one hand, the resonance field increased linearly with frequency as expected from uniform mode theory and yielded a Landégfactor in the range 1.48–2.05. On the other hand, there is no clear correlation between FMR linewidths and frequency. Inhomogeneity-based line-broadening mechanisms, due to the damping of surface/interface effects and interparticle interaction, affect the FMR effective linewidth.
Highlights
The recent emphasis on nanomaterials for various applications related to spintronics [1, 2], magnetic recording media [3], and magneto-optics [4, 5] has generated considerable interest in several magnetic metal-dielectric systems which have previously received very little attention
We have presented a detailed study on the magnetization and ferromagnetic resonance (FMR) response of Ni/ZnO and Ni/γ-Fe2O3 NCs
The immediate conclusions that we can make from the experimental results presented above are as follows: (i) the analysis of the FMR spectra can be interpreted as arising from aggregates of magnetic nanoparticles, each of which resonates in an effective magnetic field composed of the applied field, the average dipolar field, and the randomly oriented magnetic anisotropy field; (ii) referring to the experimental data, it has been established that inhomogeneity-based line-broadening mechanisms, due to the damping of surface/interface effects and interparticle interaction, affect the FMR effective linewidth
Summary
The recent emphasis on nanomaterials for various applications related to spintronics [1, 2], magnetic recording media [3], and magneto-optics [4, 5] has generated considerable interest in several magnetic metal-dielectric systems which have previously received very little attention. There are many instances in which we would like to control the microwave properties of nanocomposites (NCs), selecting from more than one possible magnetic component by adjusting for example parameters of exchange interaction between the individual constituents or, the magnetization-polarization coupling in multiferroic oxides through product property [6,7,8,9,10]. A key feature of these approaches is the use of core-shell structures in which the metal nanograins are insulated by insulating layers, the conductivity of the system will be dramatically decreased, leading to a significantly reduced eddy current loss, while the coupling strength between neighboring magnetic aggregates can overcome the anisotropy and demagnetizing effect
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