Magnetic Properties and Neutron Diffraction Study of the Chlorofluoride Series Ba2MM′F7Cl (M, M′=Mn, Fe, Co, Ni, Zn)

Abstract

The magnetic properties of the new chlorofluoride series Ba2MM′F7Cl (M,M′=Mn, Fe, Co, Ni, Zn) have been investigated by susceptibility and magnetization measurements on powder or single-crystal, Mössbauer spectrometry, and neutron diffraction experiments. Our results allow a direct comparison with the magnetic behavior of the well-known series BaMF4(M=Mn, Fe, Co, Ni, Cu, Zn), whose structure is closely related to the chlorofluoride structure. High-temperature series expansion has been used in the case of the manganese and nickel compounds to determine the average magnetic exchange parameter. Mössbauer acquisitions on the Ba2FeMF7Cl series show that, despite the close similarity between the magnetic susceptibilities, hyperfine structure is greatly disturbed by chlorine substitution. The other main difference between both series is the absence of the spin–flop transition observed on the manganese fluoride and in the field-dependent transition observed on the nickel chlorofluoride. Indeed, the field dependence of the magnetization of a Ba2Ni2F7Cl single crystal shows the existence of a magnetic transition when (H) is parallel to (c). The determination of the magnetic structure of Ba2Ni2F7Cl by neutron powder diffraction allows us to propose a qualitative explanation of this transition. We also report the magnetic structure determination in the case of the cobalt compound. In both cases (Ni or Co compounds), the magnetic structures are closely related to those of the corresponding fluorides. The magnetic structure of the mixed compounds Ba2MnNiF7Cl and Ba2FeCoF7Cl are also reported.