Magnetoelectric Effect and Magnetodielectric Effect in Magnetic Nanoparticles.

摘要

Nano-sized magnetic particles represent considerable interests in modern science because their properties are advantageous to applications such as data storage and medical science. In particular, superparamagnetism is a magnetic property which is found in nano-sized (approximately less than 20 nm) ferromagnetic or ferrimagnetic particles. Studies have shown that superparamagnetic material shows ferromagnetic magnetization only with an external magnetic field; without an external magnetic field, it loses magnetic properties even at ambient temperature overcoming its intrinsic anisotropy energy. From a magnetic memory standpoint, as bit size decreases, superparamagnetism is a major obstacle to thermal stability due to this volatility, resulting in a loss of information. If it is possible to modulate the superparamagnetic properties of magnetic nanoparticles, this might provide a solution to this critical issue.;In this dissertation, we studied the modulation of superparamagnetic properties by applying an electric field on a magnetoelectric composite composed of magnetic nanoparticles and a piezoelectric substrate. The magnetoelectric effect might present an additional solution to memory device in terms of reducing writing energy by using an electric field rather than an electric current. Additionally, for systems lacking a significant magnetoelectric coupling (for instance, magnetic nanoparticles incased in polymer resin), the relationship between the dielectric constant, which is intrinsically related to ferroelectric order, and magnetic anisotropy energy was investigated.