Nuclear Magnetic Relaxation in Magnetite

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Abstract
The nuclear magnetic relaxation times in Fe 3 O 4 have been measured. The experimental values of T 1 and T 2 range from 1.4 sec to 0.4 ms between 4.2° and 300°K. For the A ion, T 1 and T 2 are roughly equal, increasing with a magnetic field, above 120°K and show the minima at about 80°and 40°K, respectively, independent of the field. For the B ion, T 1 and T 2 are independent of the field with T 1 / T 2 ≈2 from 130°K to 300°K. The results are explained semi-quantitatively by the effect of the electron migration in the B sites. Detailed calculations show: (1) T 1 and T 2 for the A ion are governed by the coupling of the nucleus with the migrating electrons through the dipolar interaction below 120°K and through the hyperfine and the A - B exchange interactions above 120°K; (2) the anisotropic and the isotropic hyperfine interactions give the essential contributions to T 1 and T 2 for the B ion, respectively.