Ferromagnetic resonance of micro- and nano-sized hexagonal ferrite powders at millimeter waves

摘要

Complex magnetic permeability and dielectric permittivity of micro- and nano-sized powdered barium (BaFe_(12)O_(19)) and strontium (SrFe_(12)O_(19)) hexaferrites have been studied in a broadband millimeter wave frequency range (30-120 GHz). Transmittance measurements have been performed using a free-space quasi-optical millimeter wave spectrometer, equipped with a set of high-power backward wave oscillators. Real and imaginary parts of dielectric permittivity for both types of micro- and nanoferrites have been calculated using analysis of recorded high-precision transmittance spectra. Frequency dependences of the magnetic permeability have been obtained from Schlomann's equation for partially magnetized ferrites. These materials show promise as tunable millimeter wave absorbers, based on their size-dependent absorption.