U NMR Measurements of UO2 in the Antiferromagnetic State

Determination of hyperfine field is important for discussing the magnetic properties quantitatively. Mossbauer 

UO2 exhibits an antiferromagnetic ordering at 30 K. The magnitude of the ordered U magnetic moment is I. 78/xb by neutron scattering [16], which is relatively large in magnetic uranium compounds. Mossbauer and NMR measurements were carried out below 30 K. While the sample for the Mossbauer measurements was prepared with natural uranium, that for the NMR measurements was prepared with isotopes enriched up to 93.01%. 

Mossbauer spectra of UO2 at 79 and 5.4 K are shown in Fig. 7.3. The spectrum at 5.4 K is the one in the antiferromagnetic state, while the spectrum at 79 K is the one in the paramagnetic state. The spectrum at 5.4 K is much broader than that at 79 K. This indicates the observation of the hyperfine field at nuclei. To determine the magnitude 

7 STUDY OF EXOTIC URANIUM COMPOUNDS USING U MOSSBAUER SPECTROSCOPY 

Plots of the hyperfine field at nuclei against the ordered magnetic moments in uranium intermetallics. Open circles are the results reported by Ref. 2. Closed circles were the results calculated in free ions of uranium atoms. Closed squares were results measured in this work. 

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