Journal of Magnetism and Magnetic Materials. Volumes 198-199, 1 June 1999,

Reference EPFL-ARTICLE-184271doi:10.1016/j.compositesa.2012.08.001View record in Web of Science Record created on 2013-02-27, modified on 2017-05-10

Composites Part A: Applied Science and Manufacturing

Sensors and Actuators A: Physical

Collagen-DNA complex.

NMR methods are successfully used in obtaining the microscopic information on the internal magnetic structure and dynamical processes in magnets. The important application of NMR in magnets is also the investigation of structure and dynamics of domain walls. In this work, it is accomplished by observation of nuclear spin echo signals of nuclei arranged in domain walls of magnets at excitation by an additional magnetic video-pulse field. We present the first systematic study of timing and spectral diagrams of magnetic video-pulse influence on the NMR two-pulse echo in a number of magnets (ferromagnets, ferrites, half metals, intermetals). It is shown that the timing diagrams showing the dependence of two-pulse echo intensity on the temporal location of a magnetic video-pulse in respect to radio-frequency pulses and spectral diagram of this influence are defined mainly by local hyperfine field anisotropy and domain walls mobility. These diagrams could be used for the identification of the nature of NMR spectra in multidomain magnetic materials and to improve the resolution capacity of the NMR method in magnets.

Timing and Spectral Diagrams of Magnetic Video-Pulse Excitation Influence on NMR Spin–Echo in Magnets

Progerties of a single-pulse echo and its secondary signals, as well as of secondary signals of a two-pulse echo of 57 Fe nuclei in lithium ferrite is studied. The experimental results obtained indicate the efficiency of a multipulse mechanism of the formation of the single-pulse echo and its secondary signals in this magnet.

On the mechanism of formation of a single-pulse echo of 57Fe nuclei in lithium ferrite

The dependences of the intensities of two-pulse and single-pulse echoes on the time of the application of the pulses of magnetostatic field (video pulses) and on the frequency of driving pulses have been investigated experimentally. The measurements were conducted on polycrystals of metallic cobalt, half-metallic Co2 MnSi and NiMnSb, and lithium ferrite. It is shown that in lithium ferrite the single-pulse echo is formed by the stimulated mechanism of excitation, whereas in the other substances that were investigated, via the distortion of the fronts of the driving pulse. The prospects of the use of video pulses for quality control of magnetic materials is substantiated.

Magnetic video-pulse action on the nuclear spin echo in multidomain magnetic materials

The results of experimental study of two-pulse stimulated echo in ferromagnets of two types are presented. Ferromagnet Co and half-metal Co MnSi 2, in which a single-pulse echo formed by the distortion mechanism of the fronts of exciting pulse is also observed, are classified among the first type. Lithium ferrite and intermetal compound MnSb characterized by the absence of single-pulse echo in them - belong to the second type. For signals of two-pulse stimulated echo in the materials of the first type a short time and a long time of relaxations are observed. The short time is about the order of value shorter less than the spin-spin relaxation time. The long time is close to the transverse relaxation time of single-pulse echo formed by the distortion mechanism. The mechanisms that provide the possible interpretations of the peculiarities of the processes of nuclear magnetic relaxation are discussed.

Two-pulse stimulated echo in magnets

The results of a NMR study of the nature of main multiple nuclear spin-echo components in lithium ferrite are presented. It is shown that the strongly relaxing echo component in lithium ferrite is formed by the stimulated mechanism similar to the one observed in this material earlier for a single-pulse echo.

T. O. Gegechkori

Papers

On the mechanism of formation of a single-pulse echo of 57Fe nuclei in lithium ferrite

Timing and Spectral Diagrams of Magnetic Video-Pulse Excitation Influence on NMR Spin–Echo in Magnets

Magnetic video-pulse action on the nuclear spin echo in multidomain magnetic materials

Two-pulse stimulated echo in magnets

Multiple NMR spin echoes in magnets : The echo structure and potential applications