Shear-elasticity anomaly in Ce/Fe multilayers

Abstract

Brillouin light-scattering experiments have been performed at room temperature to determine the shear modulus C{sub 44} of Ce/Fe multilayers (in their reference frame) as a function of the modulation wavelength {Lambda}. The study is complementary to a previous investigation of the flexural modulus E{sub F} of this system in the sense that, while E{sub F} is dominated by the Fe layers, C{sub 44} largely reflects the elasticity of the more compliant Ce component. In the heterostructures, the Ce layers exhibit a laminated two-phase structure composed of low-volume {alpha} and high-volume {gamma}-like Ce, with a thickness-dependent relative fraction. Furthermore, structural transitions occur from an amorphous phase to the 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 {Angstrom}. These structures and phase transitions are reflected in the variation of C{sub 44} with {Lambda}. A large portion of this variation can be ascribed to the {Lambda}-dependent {alpha}-{gamma}-like composite structure of the Ce layers. A superposed softening of C{sub 44} is essentially the signature of the amorphous-to-crystalline transition in the Ce sublayers. {copyright} {ital 1997} {ital The Americanmore » Physical Society}« less