Study of Ferromagnetic Resonance of Micro and Nano Size Barium Ferrite Powders

Abstract

Complex dielectric and magnetic properties of micro- and nano-size hexagonal ferrites have been studied. Two different measurement techniques as shown in Fig. 1 have been applied to characterize the samples in the broad frequency range from 1.7 GHz to 120 GHz. It was observed that the constitutive material properties, namely permittivity and permeability, as well as the ferromagnetic resonance frequency of the samples vary with the change in particle dimensions. Based on the results of these measurements, a model for calculating the ferromagnetic resonance frequency of ferrite powders has been derived, which takes into account the size and shape of the particles in the sample. Since the properties have been found to be size dependent, it is important that the measurement set-up is accurate enough to detect these differences. In the past, the powder samples have been diluted with conductive materials or epoxy to fabricate a solid sample for measurements. The procedure followed in this study does not use any such additive. Therefore, the properties of the samples can be determined precisely. The results presented in Fig. 2 reveal that the ferromagnetic resonance frequency of the ferrite samples varies with the particle size. Therefore, the material can be tuned to resonate at different frequencies by changing the size of the particles. The resonance observed in the case of nanoparticles is much sharper than that observed for bulk samples or samples containing micro-sized particles. Absolutely no resonance was observed in case of samples that did not contain the proper phase of barium hexaferrite. The techniques developed in this study can be used for non-destructive testing to check if the desired phase has been achieved or not. Accurate characterization would allow scientists to utilize nanomaterials to their full potential and achieve high performance in diverse applications.