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Nuclear Magnetic Resonance in Ferrimagnetic Mn Fe 2 O 4

Nuclear Magnetic Resonance in Ferrimagnetic Mn Fe 2 O 4 The Mn 55 nuclear magnetic resonance has been studied in Mn Fe 2 O 4 . The unpulled resonance frequency extrapolated to 0°K is 587 Mc/sec. By studying the effect of an external magnetic field on the resonance it was determined that the main line at low temperatures arises from nuclei within the bulk of the single domains; and that the hyperfine coupling constant A is negative. The form of the single-domain enhancement factor was verified. At higher temperatures, the signal comes from nuclei within the domain walls. Frequency pulling effects associated with both the wall nuclei and bulk nuclei are observed in the liquid-helium temperature range. The temperature dependence of the Mn 55 frequency was used to study the temperature dependence of the A -site sublattice magnetization. The results are in excellent agreement with the predictions of spin-wave theory as applied to the spinel lattice. A precise cancellation of two T 5 2 terms arising, respectively, from the k 4 terms in the acoustic mode dispersion relation and the k -dependent transformation coefficients to diagonal spin-wave variables gives detailed information on ω ( k ) as well as a sensitive test of ferrimagnetic spin-wave theory. The effect on the nuclear resonance of very small anisotropy in the ferromagnetic system is discussed. In the event of a near crossover of the unperturbed nuclear and ferromagnetic uniform precession frequencies, the NMR line is shifted toward lower frequencies. This shift and the accompanying broadening are compared with the experimental observations in the vicinity of 250°K where such a crossover is expected. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review American Physical Society (APS)

Nuclear Magnetic Resonance in Ferrimagnetic Mn Fe 2 O 4

Heeger, A. J; Houston, T. W
Physical Review , Volume 135 (3A) – Aug 3, 1964
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Publisher
American Physical Society (APS)
Copyright
Copyright © 1964 The American Physical Society
ISSN
1536-6065
DOI
10.1103/PhysRev.135.A661
Publisher site
See Article on Publisher Site

Abstract

The Mn 55 nuclear magnetic resonance has been studied in Mn Fe 2 O 4 . The unpulled resonance frequency extrapolated to 0°K is 587 Mc/sec. By studying the effect of an external magnetic field on the resonance it was determined that the main line at low temperatures arises from nuclei within the bulk of the single domains; and that the hyperfine coupling constant A is negative. The form of the single-domain enhancement factor was verified. At higher temperatures, the signal comes from nuclei within the domain walls. Frequency pulling effects associated with both the wall nuclei and bulk nuclei are observed in the liquid-helium temperature range. The temperature dependence of the Mn 55 frequency was used to study the temperature dependence of the A -site sublattice magnetization. The results are in excellent agreement with the predictions of spin-wave theory as applied to the spinel lattice. A precise cancellation of two T 5 2 terms arising, respectively, from the k 4 terms in the acoustic mode dispersion relation and the k -dependent transformation coefficients to diagonal spin-wave variables gives detailed information on ω ( k ) as well as a sensitive test of ferrimagnetic spin-wave theory. The effect on the nuclear resonance of very small anisotropy in the ferromagnetic system is discussed. In the event of a near crossover of the unperturbed nuclear and ferromagnetic uniform precession frequencies, the NMR line is shifted toward lower frequencies. This shift and the accompanying broadening are compared with the experimental observations in the vicinity of 250°K where such a crossover is expected.

Journal

Physical Review – American Physical Society (APS)

Published: Aug 3, 1964

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