Uniaxial pressure-induced half-metallic ferromagnetic phase transition in ${\mathrm{LaMnO}}_3$

We use first-principles theory to predict that the application of uniaxial compressive strain leads to a transition from an antiferromagnetic insulator to a ferromagnetic half-metal phase in ${\mathrm{LaMnO}}_3$. We identify the Q2 Jahn-Teller mode as the primary mechanism that drives the transition, indicating that this mode can be used to tune the lattice, charge, and spin coupling. Applying $\simeq 6$ GPa of uniaxial pressure along the [010] direction activates the transition to a half-metallic $\mathit{pseudocubic}$ state. The half-metallicity opens the possibility of producing colossal magnetoresistance in the stoichiometric ${\mathrm{LaMnO}}_3$ compound at significantly lower pressure compared to recently observed investigations using hydrostatic pressure.

Figure 1

Calculated ground-state $Pbnm$ orthorhombic crystal structure of ${\mathrm{LaMnO}}_3$ showing ${\mathrm{MnO}}_6$ octahedra tilts, rotations, and JT distortion along with the long $\left(l\right)$, medium $\left(m\right)$, and short $\left(s\right)$ Mn-O bonds and A-AFM spin ordering.

Figure 2

Energy of FM and AFM magnetic orderings relative to A-AFM ground-state energy as function of decreasing $b$ lattice parameter.

Figure 3

Evolution of (a) the structural parameters and volume, and of (b) the Q2 and Q3 JT modes as a function of $b$. Q2 and Q3 are defined as $Q2=2(l-s)/\sqrt{2}$ and $Q3=2(2m-l-s)/\sqrt{6}$. (c) and (d) The top view of the lowest energy structures before (#) and after the structural transition (x). The inset in (a) shows the volume change around the transition.

Figure 4

(a) Evolution of the electronic band gap and total energy difference as a function of $b$. Between $b=5.53$ Å and $b=5.52$ Å, the systems undergoes an IMT and a magnetic phase transition. (b) Spin-up and spin-down projected density of states (PDOS) before and after the transition, showing the transition insulating (top panel) to metallic (bottom panel) phases.

Figure 5

Evolution of the diagonal components of the stress tensor as a function of $b$ cell parameter. Note, the off-diagonal terms remain zero for all the values of $b$ considered.