ELASTIC ANOMALY IN AN ITINERANT-ELECTRON ANTIFERROMAGNET.

The anomalous temperature dependence of an elastic constant c//1//1 in antiferromagnetic metals, e. g. fcc Mn alloys, is studied. The c//1//1 is generally written in terms of a wave-vector dependent electron density susceptibility. This susceptibility in an itinerant-electron antiferromagnet may be calculated by using the extended random phase approximation including the exchange interaction. By numerical calculations in the tight-binding single band approximation, it is shown that c//1//1 decreases with increasing energy gap caused by the antiferromagnetic spin ordering both in fcc and bcc lattices. Especially for an fcc antiferromagnet with relatively large e/a ratio, there exists a certain critical value of the energy gap where c//1//1 becomes zero as the temperature is reduced from the Neel temperature T//N. For a bcc antiferromagnet, there appears a remarkable gap of c//1//1 at T//N.