The rare-earth (or lanthanide) group-V compounds, also called pnictides form a fascinating family of materials. They can be either semimetallic or semiconductors but have interesting magnetic and electronic properties due to the presence of strongly correlated electrons in the partially filled 4f shell. The figure above is one of our latest results on DyN and shows the interesting hybridization of the minority spin 4f band with the N-2p bands leading to a valence band maximum that is entirely minority spin while the conduction band minimum is majority spin.
We started studying these materials in the early 90s together with Andre Petukhov, focusing on ErAs’s Fermi surface and magnetotransport properties in resonant tunneling devices. Later we applied the LSDA+U approach to the family of rare-earth nitrides, and also studied the related Gd pnictides and Eu chalcogenides as bulk ferromagnetic (or antiferromagnetic) semiconductors. Most recently we have applied the QSGW approach to some of them. We collaborated with a group in New Zealand at the MacDiarmid Institute in Victoria University at Wellington, (Joe Trodahl and Ben Ruck) through a World Material Network funded by NSF.
Relatedly rare-earth elements are also of interest as dopants in regular semiconductors, such as GaN both because of their interesting light emission from the intra-4f transitions and because of their magnetic properties. In particular, Gd doped GaN has received a lot of attention after the claims of colossal magnetic moments and ferromagnetism above room temperature even in the extremely dilute limit of parts per million. We studied the related defect induced magnetism with graduate student Chandrima Mitra and a visiting student, Alexander Thiess from the Peter Grünberg Institut in Jülich, Germany.
The above figure shows magnetic moments induced on N atoms as spheres proportional to the size of the moment, near Ga vacancies indicated as green cubes calculated with the KKRnano approach.