This thesis is concerned with the study of the dynamic properties of magnetic nanoparticle fluids, which are an important class of physical systems where microscopic magneto-mechanical effects can be manifested. There are two processes involved with the dynamic properties of a magnetic nanoparticle: (a) the magnetic relaxation effect that is due to the rotation of the magnetic moment of the nanoparticle, which can be due to Brownian or Néel relaxation or a combination of both, and (b) the magnetic resonance effect which is due to the precession of the magnetic moment of the magnetic nanoparticles. The parameter we can quantify is the complex magnetic susceptibility, which is frequency, and magnetic field dependent and can be estimated by impedance measurements. The complex magnetic susceptibility provides information on the microscopic parameters of a magnetic nanoparticle, namely the nanoparticle radius, the magnetic radius, the anisotropy constant, the internal anisotropy field and the gyromagnetic ratio. Applications of the magnetic susceptibility data involve estimation of power losses and heat transfer, which can be quantified by use of the tanδ loss parameter and the energy density heat loss. TARA (Trinity's Access to Research Archive) has a robust takedown policy. Please contact us if you have any concerns: rssadmin@tcd.ie