Antiferromagnetic transitions in tetragonal-like BiFeO ₃

Recent studies have reported the existence of an epitaxially stabilized tetragonal-like ("T-like") monoclinic phase in BiFeO ₃ thin films with high levels of compressive strain. While their structural and ferroelectric properties are different from those of rhombohedral-like ("R-like") films with lower levels of strain, little information exists on magnetic properties. Here, we report on a detailed neutron scattering study of a nearly phase-pure film of T-like BiFeO ₃. 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 T _N=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 T _N=260 K. The coexistence of the two magnetic phases in T-like BiFeO ₃ and the difference in ordering temperatures between R-like and T-like systems is explained through simple Fe-O-Fe bond distance considerations.