Abstract The nuclear and magnetic structures of the perovskite-structured compound KMnF3 have been investigated using high resolution neutron powder diffraction techniques for the first time. Data have been collected in… Click to show full abstract
Abstract The nuclear and magnetic structures of the perovskite-structured compound KMnF3 have been investigated using high resolution neutron powder diffraction techniques for the first time. Data have been collected in 1 K intervals from 105 K to 10 K to characterize previously identified structural phase transitions from Phase II (space group I4/mcm) – (88 K) Phase III (space group Cmcm) – (82 K) Phase IV (space group Pnma) using the diffractometer HRPD. In the temperature interval 91 K ≥ T ≥ 75 K, KMnF3 exhibits a temperature-dependent phase coexistence between phases with space groups I4/mcm and Pnma, contrary to the earlier interpretation, with no evidence found for a discrete phase with space group Cmcm. A recent revision of the space group of phase IV from Pnma to B21/m is critiqued and shown to be inconsistent with the neutron diffraction data. The magnetically ordered phases of KMnF3, collinear antiferromagnet for 81.5 K ≤ T ≤ 88.3 K, and canted antiferromagnet with a ferromagnetic component for T ≤ 81.5 K, have been investigated in detail in the temperature interval 90 K–83 K, in 0.2 K steps using the cold neutron diffractometer WISH, supplemented by lower temperature measurements using HRPD. At a temperature of ∼86.8 K, magnetic scattering is observed consistent with the development of a G-type spin configuration in the majority tetragonal phase with a moment direction parallel to the c-axis, propagation vector k = 0, magnetic space group I4/mcm. Below 75 K, in the pure orthorhombic phase, KMnF3 is found to inherit the G-type ordering parallel to c in magnetic space group Pn′ma’ which in addition permits A-type antiferromagnetic ordering, and ferromagnetic ordering along the a- and b-axes respectively.
               
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