Specific heats of and magnetic ordering in (4-Cl(py)H)3Fe2Br9, (4-Br(py)H)3Fe2Br9, and (4-Cl(py)H)1.1(4-Br(py)H)1.9Fe2Br9

The magnetic ordering in the three title materials, all tetrabromoferrates(III), was characterized. The three substances, (4-Cl(py)H)3Fe2Br9, (4-Br(py)H)3Fe2Br9 and (4-Cl(py)H)1.1(4-Br(py)H)1.9Fe2Br9, display two closely-spaced lambda-anomalies in their specific heats. The magnetic ordering phenomena in the three compositions are three-dimensional in nature, as is evident from the magnetic entropy distributions.