MBE growth and characterisation of light rare-earth superlattices

The molecular beam epitaxy growth techniques which have already successfully produced a range of heavy rare-earth superlattices have now been extended to produce superlattices of two light rare-earth elements, Nd/Pr, as well as superlattices and alloy films of a heavy/light system, Ho/Pr. High-resolution X-ray diffraction analysis shows the Nd/Pr superlattices to be of high structural quality, while the Ho/Pr superlattices are significantly less so.

In the Ho/Pr superlattices, Pr is found to retain its bulk dhcp crystal structure even in thin layers (down to 6 atomic planes thick) sandwiched between thick layers of hcp Ho. In addition, neutron diffraction studies of the He/Pr superlattices have shown that the helical Ho magnetic order is not coherent through the dhcp Pr layers, in contrast to previous hcp/hcp superlattices Ho/Y, Ho/Lu and Ho/Er.

The series of Ho:Pr alloy films has shown structural trends similar to bulk alloys, with a range of compositions between Ho0.55Pr0.45 and Ho0.35Pr0.65 where the Sm delta-structure is stable, separating more extensive regions of hcp and dhcp solid solutions.