DEFECTS IN CRYSTALS.
Final technical rept. Jan-Dec 68,
OXFORD UNIV (ENGLAND) DEPT OF THEORETICAL PHYSICS
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Three rather separate projects related to the properties of defects in crystals have been pursued during the year. 1 The effect of defects on the thermal expansion of crystals. It has been shown that defects with low frequency resonances in the vibrational spectrum may show anomalously large thermal expansion at low temperatures which should be readily observable. The mean square displacement of such impurities is large and this accentuates the anharmonic properties. 2 Spin waves in a crystal containing point defects. The theory applicable at 0 degrees K when the magnetic moments are aligned is well established. Preliminary attempts have been made to extend this to T approximately equal to T sub c and T T sub c, but a satisfactory theory has not been achieved. 3 Spin wave interactions in antiferromagnets. In the two magnon optical properties of antiferromagnets the spin waves are created close together and the interaction effects are accentuated. It has been shown that the observed spectra may be accounted for if these interactions are included. Author
- Solid State Physics