DYNAMIC CONTROL OF ELASTICITY BY MEANS OF ULTRASOUND EXCITATION IN ANTIFERROMAGNETS

Sound velocity control by resonance ultrasonic oscillations in a magne toordered medium is demonstrated experimentally on a sample of alpha-F e2O3 single crystal. The phenomenon is caused by giant nonlinearity in troduced by the crystal magnetic subsystem into the elastic one. The s ensitivity of the dynamic elasticity control obtained in the experimen t is (Delta v/v)/a(p)(2) = 10(-5) ppm(-2), where Delta v is the variat ion of sound velocity under an ultrasonic deformation of the amplitude a(p). From another side, the acoustically induced static deformation caused by the magnetoelastic nonlinearity is estimated, for the same e xperimental conditions, as 0.64 ppm when an alternative deformation of amplitude a(p) = 20 ppm is applied. As it is shown both values are co upled in agreement with the theory. (C) 1998 Elsevier Science B.V. All rights reserved.