Spectroscopy and confocal imaging of complex ferroic systems

Abstract

New applications of ferroic systems often consider domain wall as carrier of information. Understanding of the nature of domain structure and its dynamics is therefore essential. At the same time the omnipresent need of keeping up with Moore law demands the dimensions of commercialized devices to decrease drastically. Hence the resolution of classical optical Kerr microscopy does not suffice anymore. Methods for studying domain dynamics at nanoscale are available, but are very time consuming and expensive. It’s extremely complicated to measure both magnetic and electric properties simultaneously. This creates a need for an intermediate method that offers sub-micron lateral resolution and short measurement times, yet produces enough information about all ferroic properties of a system. To address this issue we developed several optical methods that expand the possibilities of multiferroic characterization. An electric field frequency spectrum magneto-optical Kerr effect setup allows for an effective separation and quantification of surface and strain mediated magnetoelectric coupling effects as demonstrated on Co/ lead zirconate titanate (PZT) ferroic multilayers. Direct electro-magnetic domain mapping with sub-micron lateral resolution was made possible with cryostat ready polarization sensitive confocal microscope. Magnetic field induced changes in ferro-electric response around 50% with 20% variations were observed on barium titanate (BTO)/ lanthanum strontium manganite (LSMO) structure. Furthermore, enhancements to magneto-optical Kerr-effect (MOKE) spectroscope enabled study of the origin of magneto-optical enhancement at plasmonic frequencies in magneto-photonic crystals. This paves the way to plasmon-devices with optimal performance for applications in optical communications and sensing. In this line, we developed a unified theoretical frame for modeling of both saturating and non-saturating magneto-optical effects in diluted colloidal dispersions of magnetic nanoparticles. The model shows remarkably good agreement with experimental data obtained from nickel nanoparticles in hexane and toluene using only tabulated data and no fitting. Hence we can envision the use of optimized hybrid metal/ dielectric composites as platforms for new optical devices and especially for innovative plasmon-based sensors exploiting light polarization instead of reflectance.

Date of Award	17 Feb 2014
Original language	English
Awarding Institution	Barcelona Institute of Materials Science (ICMAB)
Supervisor	Javier Rodriguez Viejo (Director)