Browsing by Author "Korppi, Maria"

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All-optical reversible switching of local magnetization
(2007) Shevchenko, Andriy; Korppi, Maria; Lindfors, Klas; Heiliö, Miika; Kaivola, Matti; Il’yashenko, Eugene; Johansen, Tom H.
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The authors demonstrate all-optical reversible switching of the magnetization direction in a uniformly magnetized ferrite-garnet film. The magnetization is switched by locally heating the film with a pulsed laser beam. The direction to which the magnetization flips is controlled by two parameters, the beam diameter and the pulse energy, and not by the direction of the external magnetic field. In the experiments, neither the magnitude nor the direction of the external magnetic field is changed. The results of this work illustrate the richness of optical methods to locally control the properties of magnetic materials and suggest all-optical device applications.
Electromagnetic field shaping for manipulation of atoms and nanoparticles
(2008) Korppi, Maria
Helsinki University of Technology | Master's thesis
Non-uniform electric and magnetic fields provide a versatile tool to manipulate and control the motional states of polarizable and magnetizable particles in a remote and non-destructive fashion. However, as the field force falls dramatically with the particle size, the manipulation of sub-micron particles against their Brownian motion at room temperature is challenging. This requires the use of strong field gradients and high intensities which makes the miniaturization of the field-producing structures preferable. Other motivations to develop miniaturized trapping structures are the improved positional control and reduced power consumption provided by them. The objective of this thesis is to pursue the realization of two novel miniaturized manipulation tools based on static electric and magnetic fields by modeling the trapping potentials, and fabricating the trapping structures. In particular, a method to fabricate a three-dimensional periodic nanoelectrode array for nanoparticle manipulation is described. The method is based on tapering a microstructured photonic crystal fiber and filling the contracted capillaries with a conductive material. Based on numerical simulations, such nanoelectrodes can be used to produce electric-field patterns with nanometer scale features for control and assembly of nanoparticles at room temperature. The other miniaturized device considered in this thesis is a permanent-magnet chip for atom and nanoparticle manipulation. Microscopic magnetic-domain patterns recorded in a ferrite-garnet (FG) film can be used to create microscopic traps for nanoparticles at room temperature and for atoms cooled to AK-range temperatures. The magnetic-domain patterns can be created by using a conventional magneto-optical recording technique. In addition, we have developed a novel technique to record the domain patterns all-optically. These techniques allow one to record and reconfigure the domain patterns in situ. In essence, arbitrary two-dimensional trapping structures can be readily produced. Our FG chip has many advantages over the conventionally used current-carrying wire structures. Most important of them are optical transparency, reconfigurability, and the ability to produce nearly noiseless and strong magnetic fields without any electric-power consumption. In our laboratory, this kind of microscopic magnetic atom traps have been demonstrated experimentally using 85Rb atoms. In all-optical recording the local magnetization direction in the FG film is controlled purely optically by adjusting the beam parameters of the recording laser. This magnetization-reversal phenomenon is intriguing from both fundamental and technological points of view and can be used not only in the magnetic chip technology, but also in other magnetic and optical device applications in which the use of electricity is undesirable. As an example, a novel concept of all-optical memory elements that allow writing and erasing of information in three dimensions, is introduced in this thesis. Both the nanoelectrode array and magnetic FG chip could be integrated with other nano- and microfabricated components to built multifunctional devices on a single substrate. With this respect, the work introduced in this thesis constitutes one more step forwards the "lab on a chip" technology.