G. J. MacDougall, H. M. Christen, W. Siemons, M. D. Biegalski, J. L. Zarestky, S. Liang, E. Dagotto, S. E. Nagler
Recent studies have reported the existence of an epitaxially-stabilized
tetragonal-like ('T-like') monoclinic phase in BiFeO3 thin-films with high
levels of compressive strain. While their structural and ferroelectric
properties are different than those of rhombohedral-like ('R-like') films with
lower levels of strain, little information exists on magnetic properties. Here,
we report a detailed neutron scattering study of a nearly phase-pure film of
T-like BiFeO3. By tracking the temperature dependence and relative intensity of
several superstructure peaks in the reciprocal lattice cell, we confirm
antiferromagnetism with largely G-type character and TN = 324 K, significantly
below a structural phase transition at 375 K, contrary to previous reports.
Evidence for a second transition, possibly a minority magnetic phase with
C-type character is also reported with TN = 260 K. The co-existence of the two
magnetic phases in T-like BiFeO3 and the difference in ordering temperatures
between R-like and T-like systems is explained through simple Fe-O-Fe bond
distance considerations.
View original:
http://arxiv.org/abs/1107.2975
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