The crystal and magnetic structures of LaCa2Fe3−xMxO8 (M=Al, Ga, In)

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<0.25x<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)μB3.8(1)μB in LaCa2Fe3O8 and 4.8(1)μB4.8(1)μB in LaCa2Fe2GaO8. The magnetic space group (P2b21′ma′) and moment direction (along c) does not appear to change with Ga substitution.