Investigation of the Magnetic Structure of KFeCl sub 3 , KFeBr sub 3 , Rb sub 2 MnCl sub 4 , and Rb sub 3 Mn sub 2 Cl sub 7 Compounds with Magnetic Correlations in One and Two Dimensions

摘要

The crystallographic structure of KFeCl sub 3 and KFeBr sub 3 consists of (FeCl) exp - octahedra packed in isolated zigzagging chains. These compounds order antiferromagnetically at Tsub(N) approximately 16 deg K and Tsub(N) approximately 9.5 deg K, respectively. Below Tsub(N) the Fe exp 2+ magnetic moments within a chain are ferromagnetically coupled, parallel to the chain axis, while the chains are coupled antiferromagnetically. In the temperatures Tsub(N) <= T < 2Tsub(N), KFeCl sub 3 has magnetic correlations within the chains only, whereas the correlations between the chains are negligible. Moessbauer effect measurements at these temperatures show a distinct hyperfine magnetic splitting, characteristic of relaxation phenomena. Cs sub 2 MnCl sub 4 , Rb sub 2 MnCl sub 4 and Rb sub 3 Mn sub 2 Cl sub 7 belong to the Asub(n+1)Bsub(n)Xsub(3n+1) family of compounds, with the Dsub(4h)sup(17) space group. These compounds order antiferromagnetically at Tsub(N) approximately 55 deg K for Cs sub 2 MnCl sub 4 and Rb sub 2 MnCl sub 4 , and Tsub(N) approximately 64.5 deg K for Rb sub 3 Mn sub 2 Cl sub 7 . Below Tsub(N) each Mn exp 2+ moment is along the c-axis and is coupled antiferromagnetically to the moments of its nearest neighbours (nn). These compounds behave like a two-dimensional antiferromagnet at T >= Tsub(N). Neutron scans of the reciprocal space exhibit rods of reflections along c vectorsup(*). The negligible interactions between next nn sets of MnCl sub 2 layers, a distance c vector apart, yield both in Rb sub 2 MnCl sub 4 and in Rb sub 3 Mn sub 2 Cl sub 7 , two distinctive magnetic structures (polytypes) below Tsub. (Atomindex citation 10:431406)