Final Report Summary - DMH (Nonlinear dynamic hysteresis of nanomagnetic particles with application to data storage and medical hyperthermia)
In the context of the project, we have developed accurate theoretical methods for evaluating the nonlinear ac stationary response of an individual single domain nanoparticle with various magnetic anisotropy potentials (uniaxial, biaxial, etc.) of both surface and volume origin in the presence of strong dc and ac magnetic fields both in the high and low damping limits. We have also extended the methods to calculating the nonlinear ac stationary response of an assembly of magnetic nanoparticles in in superimposed dc and ac magnetic fields. Furthermore, we have developed effective methods of calculation of the DMH in an individual nanoparticle and assemblies of nanoparticles with randomly oriented easy axes and we have analyzed the dependence of the area of the DMH loops on the temperature, frequency, and ac and dc bias field magnitude and orientation. By generalizing these results to the calculation of the nonlinear susceptibility and energy absorption of ferrofluids, we have also elaborated efficient methods of calculation of nonlinear DMH in liquid suspensions of magnetic nanoparticles. Theoretical predictions have been compared with relevant experimental data comprising the magnetization dynamics of nanoparticles driven by a strong ac field with particular application in magnetic hyperthermia. Hence, we have achieved all the anticipated objectives set out in our project.
The results obtained may have many applications, two of the most important being: magnetic moment switching (under pulsed fields) and heat generation (under oscillating fields). The first is important from the viewpoint of magnetic data storage, the second - for the development of magnetically induced hyperthermia not exclusively for medical applications. Besides the medical uses, DMH can also be used to characterize the recording density, signal-to-noise ratio, etc., in a given nanogranular medium. Furthermore, by accounting for the effect of thermally activated magnetization reversal (superparamagnetism), we can model switching processes for any desired field- temperature-thermomagneticprotocol, e.g. heat-assisted or hybrid magnetic recording techniques. As far as biomedical applications are concerned, one of the most promising thermal approaches which has recently received considerable attention is local magnetic hyperthermia. This utilizes ac magnetic field energy absorption by nanosized ferromagnetic particles syringed into the tumor. In addition to the above mentioned applications to ferromagnetic hyperthermia and data storage technologies we expect that our studies have substantially increased our knowledge concerning such promising trends in experimental techniques as microrheometry of complex (including biological) liquids employing small magnetic particles.