Weak-ferromagnetism of CoF3 and FeF3

Abstract

Cobalt trifluoride CoF3 and Iron trifluoride FeF3 are known as a G-type antiferromagnetic structure in the R-3c rhombohedral crystal structure. The neutron powder diffraction study had been reported that Co antiferromagnetic spin direction is parallel to 3-fold crystal axis in CoF3 whereas Fe antiferromagnetic spin direction is perpendicular to 3-fold crystal axis in FeF3. However, the resolution of early neutron powder diffractometer is not enough to distinguish between (003)h and (101)h rhombohedral magnetic peaks definitely.We employed high-resolution powder neutron diffractometer(SuperHRPD) at room temperature in MLF, J-PARC. The time-of-flight neutron powder diffractometer distinguishes clearly between (003)h and (101)h magnetic peaks. Then, we confirmed the proposed magnetic structural models of CoF3 and FeF3 at room temperature. In a magnetic susceptibility, CoF3 displays the additional magnetic anomaly at T* = 40 K. We discussed possible weak-ferromagnetism by the interplay of spin tilting and Dzyaloshinski-Moriya interactions.