Strain Induced Half-Metal to Semiconductor Transition in GdN

Abstract

We have investigated the electronic structure and magnetic properties of GdN as a function of unit cell volume. Based on the first-principles calculations of GdN, we observe that there is a transformation in conduction properties associated with the volume increase: first from halfmetallic to semi-metallic, then ultimately to semiconducting. We show that applying stress can alter the carrier concentration as well as mobility of the holes and electrons in the majority spin channel. In addition, we found that the exchange parameters depend strongly on lattice constant, thus the Curie temperature of this system can be enhanced by applying stress or doping impurities.

Magnetic Interaction between Surface-Engineered Rare-Earth Atomic Spins

“…The GdN bulk, being a ferromagnetic semiconductor, has been studied experimentally by photoemission and computationally by the ''local spin density approximation plus the Coulomb repulsion parameter'' (LSDA þ U) method for its potential application in spintronics. Following previous LSDA þ U studies of GdN bulk [16,23], we find that U f ¼ 6:7 eV and J f ¼ 0:7 eV yield the energy difference between the majority-spin Gd 4f and N 2p states in best agreement with photoemission measurements [24,25]. This set of U f and J f are used in our succeeding PBE þ U calculations of both the GdN bulk and the Gd dimer on the CuN surface.…”

“…This can be interpreted as follows: The Gd 5d electrons in the GdN bulk join the conduction electron sea, and consequently they contribute to the RKKY interactions but they do not form a directional orbital interaction in between two Gd as in the surface dimer case. Although the ferromagnetism seems to be understood quite well by RKKY interaction, the GdN-bulk study [23] does not exclude the possibility of a ferromagnetic contribution from the 90 -superexchange interaction, which those authors note can be quite large in some oxides. Indeed, from our finding of superexchange that becomes ferromagnetic at an angle of 112 , we predict that the 90 coupling in bulk material has at least some ferromagnetic superexchange as well.…”

“…7(a), where it can clearly be seen that there is no obvious spin-density lobe connecting two Gd atoms, i.e., no spin bonding in a GdN bulk. In fact, a previous DFT study of GdN [23] has already concluded that the ferromagnetism of the diagonal nearest neighbors most likely originates from the RKKY interaction; the authors of [23] analyzed the trends of exchange coupling of differently strained GdN compared to all other gadolinium pnictides of larger-size anions. RKKY is quite prominent in Gd bulk compounds, compared to a pair of surface adatoms, because of the increased free-electron density of states contributed by all of the Gd.…”

Fully opposite spin polarization of electron and hole bands in DyN and related band structures of GdN and HoN

“…To what extent the Curie temperatures from theory and experiment agree is still controversial. 5,7,11 This results from the sensitivity of the exchange interactions to details of the calculations, lattice constant, which density functional or band-structure method is used, and, again, on the possible additional carrier mediated effects. While a lot of the experiment and theory has been focused on the half-filled f shell case of GdN, the situation is less clear for other RE-nitrides.…”

“…These effects are furthermore sensitive to the lattice constants. 7 Therefore, it is no surprise that the electronic and magnetic properties of these materials continue to be controversial.…”