R. Gebauer et al., Noncolinear spin polarization from frustrated antiferromagnetism: A possible scenario for molecular oxygen at high pressure, PHYS REV B, 61(9), 2000, pp. 6145-6149
We perform density-functional calculations of the magnetic properties of a
simplified structure aimed at capturing some of the features of the elusive
epsilon phase of molecular oxygen at high pressure. Starting with the delt
a phase-which is a quasi-two-dimensional distorted triangular arrangement o
f antiferromagnetically ordered molecules-pressure could decrease the bla r
atio in the basal planes pushing it toward the ideal triangular value of 1/
root 3, thus increasing magnetic frustration. We conjecture that when frust
ration takes over, the magnetic order may turn into a 120 degrees planar sp
in-spiral structure inside the epsilon phase, until at higher pressures han
d-overlap metallization suppresses magnetization in the zeta phase. This co
njecture is substantiated by calculations that also represent the attempt t
o apply state-of-the-art pseudopotential techniques to the magnetic propert
ies of a frustrated antiferromagnet.