Broadband Ferromagnetic Resonance Measurements in Ni/ZnO and Niγ-Fe2O3Nanocomposites

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.

Room-temperature ferromagnetism in Li-dopedp-type luminescent ZnO nanorods

“…12 Such broad line at room temperature as observed for ZnO:Li nanocrystalline powder corresponds to FMR and is a clear indication that ferromagnetic ordering is present in ZnO:Li at room temperature. Such FMR has been reported for Mn-doped ZnO pellets 22 and quantum dots; 23 ZnO:Ni 24 and ͑Ga,Mn͒As. 25 PL excitation ͓Fig.…”

High temperature carrier controlled ferromagnetism in alkali doped ZnO nanorods

“…20͒ and ZnO:Na nanocrystalline powder samples. Such broad FMR spectra has also been reported for Mn 2+ doped ZnO pellets sintered at 500°C, 8 Mn 2+ doped ZnO quantum dots, 21 Ni/ZnO, 22 and ͑Ga,Mn͒As.…”

Microwave absorption measurements using a broad-band meanderline approach

“…One of the key features is the design of the probe utilized to measure the electromagnetic response from the sample. Motivated by the patterned microstrip configurations employed in some FMR measurements, [9][10][11][12][13][14][15] we utilize a meanderline. Figure 1 illustrates schematically an outline of the device, which generates rf magnetic fields that are both in plane and out of plane with respect to the sample.…”