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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Magnetic exchange coupling in hard-soft ferromagnetic composite thin films of CoPt-Co : role of processing and structure /

Kim, Jihwan, January 2001 (has links)
Thesis (Ph. D.)--Lehigh University, 2001. / Includes vita. Includes bibliographical references (leaves 230-239).
2

On strain-mediated magnetoelectric effects in multiferroic composite nanostructures

Chen, Haitao, 陈海涛 January 2013 (has links)
Multiferroics which combine two or more order parameters of ferroelectricity, ferromagnetism and ferroelasticity, have drawn great interests in the past few years due to their promising potential of application in sensors, transducers, spintronics and multistate memories. Coupling between the ferroelectricity and ferromagnetism renders the induction of an electric polarization P upon applying a magnetic field, or the induction of a magnetization M upon applying an electric field which is called magnetoelectric coupling effect. There are single phase multiferroics which simultaneously possess ferroelectricity and magnetism in nature. However, these natural multiferroics only exhibit weak magnetoelectric coupling effect at very low temperature which hinders the practical applications. An alternative and more promising choice is to fabricate multiferroic composites. In the multiferroic composite systems, large magnetoelectric coupling effects can be produced indirectly from the strain-mediated interaction even at room temperature and great design flexibility can be obtained. In the present study, two types of multiferroic composite nanostructures are investigated: the vertical heteroepitaxial multiferroic thin films and film-on-substrate heterogeneous bilayers with incorporation of various influences, such as film thickness, misfit strains and flexoelectricity. Since the first fabrication of vertical epitaxial multiferroic nanostructures, great scientific interests have been attracted for the potential large magnetoelectric effects arising from the relaxed substrate constraint and large interfacial area between the ferroelectric and ferromagnetic phases. A three dimensional phase field model is devised to precisely describe the complex strain state of this nanostructure. The simulation results demonstrate that both film thickness and misfit strains are important in determining the magnitude of magnetoelectric effect. Due to the strong strain-mediated magnetoelectric coupling effect in film-on-substrate system with a ferromagnetic thin film directly growing on a thick ferroelectric substrate, precision electric control of local ferromagnetism, i.e. ferromagnetic domain pattern and domain wall properties, are achievable. The results show that the domain pattern of the ferroelectric substrate can be fully transferred onto the as-deposited ferromagnetic thin film. High stability of the magnetic domain is observed when the system is subjected to an external magnetic field. Under an applied electric field, the transferred domain pattern in magnetic film can be either maintained or erased depending on the direction of applied electric field. Moreover, when a pulse of in-plane electric field is applied, the magnetic domain wall motion can be observed in concurrence with the ferroelectric domain wall motion. With the decrease of material size, some effects that can be neglected in bulk materials may play an important role on the overall properties of material, such as flexoelectric effects which describe the induction of polarization from strain gradient. A two dimensional phase field model is adopted to study the influence of flexoelectric effects on the epitaxial ferroelectric films. A thermodynamic phenomenological model is then utilized to analyze the influence of flexoelectric effects on magnetic field induced electric polarization in the multiferroic nanocomposite bilayers. By decreasing the film thickness, the induced polarization from flexoelectric effects becomes more and more dominant and finally overcomes the electrostrictive induced polarization which is dominant when film thickness is large. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy
3

Electronic structures and magnetic properties of MnTe in the NiAs polymorph under pressure

Yeh, Hong-chieh 20 July 2006 (has links)
The spin polarized first principles pseudofunction (PSF) method with the local spin density approximation (LSDA) has been used to calculate total energies, electronic structures and total and partial densities of states for bulk MnTe in the NiAs structure for both anti-ferromagnetic and ferromagnetic states under the pressure. For the pressure range considered in this study, the anti-ferromagnetic state is thermodynamically more stable than the ferromagnetic state in agreement with experimental observation. For the anti-ferromagnetic state, MnTe has an indirect band gap, which decreases linearly with the increase of the pressure in agreement with experiment. The calculated valence band and conduction band are found to broaden with the increase of the pressure, which can be attributed to the pressure induced shortening of the Mn-Te bond length that enhances hybridization between Mn and Te orbitals.
4

Scale and stress effects on the behavior of ferromagnetic materials

Hu, Ruilong., 胡瑞龍. January 2007 (has links)
published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy
5

Spin fluctuations in itinerant electron ferromagnets

Taillefer, L. January 1986 (has links)
No description available.
6

The tight-binding torque-method for the exchange coupling in magnetic multilayers

Robinson, Alex Martin January 1997 (has links)
No description available.
7

Hyperfine interactions of holmium in single crystals of magnetic compounds

Lataifeh, Mahdi Salem Q. M. January 1989 (has links)
No description available.
8

Computer analysis of the incidence of ferro-nonlinear ?-oscillations in power circuits

Al-Azzawi, Z. T. January 1984 (has links)
No description available.
9

Investigation of magnetic microstructures using novel transmission electron microscopy techniques

Johnston, Alan Biggar January 1995 (has links)
No description available.
10

Critical properties of dipolar ferromagnetics

Wragg, M. J. January 1988 (has links)
No description available.

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