SHEAR-ELASTICITY ANOMALY IN CE FE MULTILAYERS

Brillouin light-scattering experiments have been performed at room tem perature to determine the shear modulus C-44 of Ce/Fe multilayers (in their reference frame) as a function of the modulation wavelength Lamb da. The study is complementary to a previous investigation of the flex ural modulus E-F of this system in the sense that, while E-F is domina ted by the Fe layers, C-44 largely reflects the elasticity of the more compliant Ce component. In the heterostructures, the Ce layers exhibi t a laminated two-phase structure composed of low-volume alpha and hig h-volume gamma-like Ce, with a thickness-dependent relative fraction. Furthermore, structural transitions occur from an amorphous phase to t he crystalline phases of bcc Fe and fcc Ce, for Fe abruptly within the entire sublayer volume at a critical thickness near 20 Angstrom, for Ce more gradually with increasing layer thickness starting near 40 Ang strom. These structures and phase transitions are reflected in the var iation of C-44 with Lambda. A large portion of this variation can be a scribed to the Lambda-dependent alpha-gamma-like composite structure o f the Ce layers. A superposed softening of C-44 is essentially the sig nature of the amorphous-to-crystalline transition in the Ce sublayers.