The crystal and magnetic structures of LaCa 2 Fe 3-x M x O 8 (M = Al, Ga, In)

Abstract

LaCa2Fe3O8 (A3B3O8) is an example of a layered structure in that it consists of pairs of octahedral, perovskite-like layers alternating with a single tetrahedral layer. This work explores the doping of non-magnetic group 13 elements, M=Al, Ga and In, onto the B-site of LaCa2Fe3-xMxO8 as a function of x. The structural and magnetic effects are examined using a combination of neutron and X-ray diffraction. Solubility limits are established. It is found that for M=Ga the solubility limit occurs between x=1.0 and x=1.25, for the synthesis conditions used, while there is evidence for low (x<0.25) but non-zero substitution of Al. Structural refinements at x=1 suggest that Ga prefers neither the tetrahedral nor octahedral sites. The magnetic structure of LaCa2Fe2GaO8 has been examined using neutron diffraction at 3.2 K and room temperature. At low temperature the staggered moment per Fe3 is 3.8(1)μB in LaCa2Fe3O8 and 4.8(1)μB in LaCa2Fe2GaO8. The magnetic space group (P2b21′ma′) and moment direction (along c) does not appear to change with Ga substitution.