Synthesis and Theoretical Study of Half-Metallic Highly-Textured Gadolinium Nitride Films

“Barry” Chin Li Cheung
Collaborator Wai-Ning Mei

Gadolinium nitride (GdN) is one of the rare-earth nitrides predicted to have both ferromagnetic and half-metallic properties. Electronic structure calculations based on local density approximations suggest that GdN has a large gap at the Fermi energy in the minority spin states. GdN is also expected to be half-metallic in majority spin states with electron and hole pockets at the Fermi surface. These remarkable features stimulate a long-standing interest in GdN as a possible material candidate for developing spin-dependent transport devices such as spin-filters, and exploring giant and tunneling magneto resistance effects. Yet the elucidation of the electronic and transport properties of GdN has long been a hard problem for investigators due to lack of high quality samples. 

The objective of this research is to study of the postulated semi-metallic nature of ferromagnetic GdN via theoretical calculations and physical property measurements. Recently, we fabricated the long postulated highly textured [100] GdN films on [100] LaAlO3 crystal using chemical vapor deposition. (See figure) Preliminary photoemission and inverse-photoemission studies reveal profound features in the density of states (DOS) and locations of 4f states below and above the Fermi energy for the band structure perpendicular to films. Nevertheless, there are still some unresolved issues. For example, the origin of the unexpected apparent band gap or low DOS region, ~2-3 eV indicated in the preliminary photoemission study is not resolved. Thus it is essential to invest additional experimental and theoretical efforts to unravel these long-standing problems related to this system.

The tasks for our research are:
1) Explore and improve the synthesis of crystalline GdN samples on designed template substrates for better physical property measurements.
2) Apply first-principle total energy local density theory together with GW corrections to study the surface and correlation effects imbedded in GdN.

We expect that the proposed combined efforts will advance the understanding of this intriguing half-metallic ferromagnetic system.

Synthesis and Theoretical Study of Half-Metallic Highly-Textured Gadolinium Nitride Films