Orientation Dependence of the Critical Magnetic Field for Multiferroic BiFeO3...

Multiferroic BiFeO3 undergoes a transition from a distorted spiral phase to a G-type antiferromagnet
above a critical field Hc that depends on the orientation m of the field. We show that
Hc(m) has a maximum when oriented along a cubic diagonal parallel to the electric polarization P
and a minimum in the equatorial plane normal to P when two magnetic domains with the highest
critical fields are degenerate. The measured critical field along a cubic axis is about 19 T but Hc is
predicted to vary by as much as 2.5 T above and below this value. The orientational dependence
of Hc(m) is more complex than indicated by earlier work, which did not consider the competition
between magnetic domains.