Two-dimensional antiferromagnetism and weak ferromagnetism in some anilinium salts of the types A2MnCl4 and A2FeCl4

Abstract

Magnetic susceptibility measurements have been made between 4.2 and 160 K on the powdered salts (4-XC6H4NH3)2MnCl4(X = F, Cl, Br, or Bun). These compounds have layer structures of the K2NiF4 type, with interlayer spacings of 15.8, 16.6, 18.8, and 23.5 A, respectively. Broad susceptibility maxima are observed at ca. 70 K, and can be fitted on the assumption of a two-dimensional exchange interaction of Heisenberg (–2JSi. Sj) form, with –J/k= 4.25, 4.50, 4.00, and 3.75 (±0.1) K, respectively. All four compounds show weak ferromagnetism below the Neel temperature (TNca. 40 K), which is attributed to spin canting in the antiferromagnetically ordered state. The transition temperature is practically independent of the layer spacing. Measurements on a single crystal of the 4-chloro-compound indicate a canting angle of ca. 0.06°, and show that the resulting magnetisation lies in the layer plane. Powder susceptibility measurements on (4-ClC6H4NH3)2FeCl4 indicate that this compound is also a two-dimensional antiferromagnet, with –J/k= 10.7 ± 0.5 K (TNca. 87 K) and a canting angle ca. 0.8° in the ordered state. Below TN the magnetic behaviour shows unusual dependence on the thermal and magnetic history of the sample, possibly due to a nearly degenerate magnetostrictive distortion.