Nuclear and magnetic structures of KMnF3 perovskite in the temperature interval 10 K–105 K

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.