First-principles study of the structural energetics of PdTi and PtTi

The structural energetics of PdTi and PtTi have been studied using first-principles density-functional theory with pseudopotentials and a plane-wave basis. We predict that in both materials, the experimentally reported orthorhombic $B19$ phase will undergo a low-temperature phase transition to a monoclinic $B19'$ ground state. Within a soft-mode framework, we relate the $B19$ structure to the cubic $B2$ structure, observed at high temperature, and the $B19'$ structure to $B19$ via phonon modes strongly coupled to strain. In contrast to NiTi, the $B19$ structure is extremely close to hcp. We draw on the analogy to the bcc-hcp transition to suggest likely transition mechanisms in the present case.Comment: 8 pages 5 figure

Magnetic properties and structure of palladium/cobalt and palladium/iron multilayers

Pd/Co and Pd/Fe multilayer films containing ultrathin Co and Fe layers were prepared by vapor deposition on substrates at room temperature. Their modulated structure, even for films containing 2-Å-thin Co and Fe layers, was proved by x-ray diffraction and transmission electron microscopy. Below a Co layer thickness of about 8 Å, the Pd/Co multilayers acquire an easy magnetic axis perpendicular to the film, which is mainly caused by magnetic interface anisotropy. This leads for multilayers containing Co monolayers to almost rectangular hysteresis loops, by which these films may be very suitable as a perpendicular magnetic recording medium. Pd/Fe multilayers also have a perpendicular interface anisotropy, but the shape anisotropy dominates. Per unit Co volume the Pd/Co multilayers have a higher saturation magnetization than pure Co, which is attributed to an induced ferromagnetism on Pd interfacial atoms