Strain Induced Half-Metal to Semiconductor Transition in GdN

We investigate 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 the conduction properties associated with the volume increase: first from half-metallic to semimetallic, 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.

Figure 1

Comparison between the calculated DOS (solid line, majority spin; dotted line, minority spin) at theoretical lattice constant ($a=4.92\AA$) and the photoemission spectra for nitrogen on Gd(0001). The new photoemission features that are not attributable to the Gd(0001) substrate compare well with the calculated DOS for GdN. Features with strong N $2p$ weight are indicated. Binding energies for experiment are shifted to higher binding energies as expected with a final state spectroscopy of a correlated electron system, but the shift is roughly uniform for key features of the photoemission spectra (taken for both $s$ and $p$ polarized light).

Figure 2

Band structure of GdN in the vicinity of the Fermi energy for three volumes: (a) at the calculated equilibrium lattice parameter $a=4.92\AA$; (b) at the lattice parameter increased by 5% ($a=5.16\AA$); (c) at the lattice parameter increased by 14% ($a=5.63\AA$). Solid and dotted lines represent spin majority and spin minority states, respectively. The change of conducting properties are indicated by the change of energy difference between the top (bottom) of the hole (electron) pockets and the Fermi energy.

Figure 3

Exchange parameters of GdN plotted as a function of the lattice constant; notice the strong volume dependence of $J_1$ and $J_2$.