Investigation of ferromagnetic resonance in magnetic fluids by means of the short-circuited coaxial line technique

Abstract

The short-circuit coaxial transmission line technique has been used to investigate ferromagnetic resonance in magnetic fluids over the frequency range 0.1-6 GHz. Measurements of the complex susceptibility, chi ( omega )= chi '( omega )-i chi "( omega ), of magnetic fluid samples of magnetite and cobalt particles, of approximate median diameters 10 and 5.8 nm are presented. The presence of loss peaks in the chi "( omega ) components at approximate frequencies of 1.2 and 2.5 GHz, respectively, coupled with the transition of the chi '( omega ) components from positive to negative values at slightly higher frequencies, is indicative of ferromagnetic resonance. Appropriate equations for the calculation of the complex susceptibility are presented.

The resonance decay function method in the determination of the pre-factor of the Néel relaxation time of single-domain nanoparticles

“…Measurements of frequency and polarizing field dependence of the complex magnetic susceptibility, χ(ω, H) = χ'(ω, H) -i χ''(ω, H), were made by means of the coaxial transmission line technique [21,22], using a Hewlett Packard (HP) 50Ω coaxial line incorporating a coaxial cell, in conjunction with an HP 8753C network analyzer. The biasing field, H, was varied between 0 and 100 kA/m.…”

Investigation of the complex susceptibility of magnetic beads containing maghemite nanoparticles

“…The higher frequency range measurements were made by the short-circuit transmission line technique [19,20] The field dependence of f res is given by 2pf res ¼ g(H+H A ) and from a plot of f res against H, the effective anisotropy field, H A , of the maghemite particles of Sample 1 was determined as being 47.8 kA/m. Using an M s of 0.4 T the anisotropy constant, K, is determined as 4 J=m 3 .…”

Brownian Motion in Biological Sensing

“…Alternatively, the pick-up coil itself can be used as the source of the alternating magnetic field and the susceptibility can be determined directly from the impedance of the coil. For measurements at very high frequencies (>0.1 GHz) a transmission line can be used instead of a pick-up coil [32].…”