For pt.I see ibid., vol.11, p.345 (1978). The metamagnetic phase transition and the associated phase diagram of the anomalous antiferromagnet CeSb were determined in a neutron diffraction study of the magnetic ordering of CeSb single crystals in applied magnetic fields parallel to the (001) and (011) directions (H<5 T). Because of the anisotropic exchange interactions that favours a (001) easy direction of magnetisation, the magnetic properties are similar to those of the Ising spin systems i.e. antiferromagnetism, ferrimagnetism and ferromagnetism occur at low temperatures and at increasing magnetic fields. The observed magnetic structures do not correspond to the stable configurations expected from the molecular field theory of the face-centred cubic lattice. The change from a first-order transition at the Neel temperature in zero field to second-order transition at high fields points to the existence of a tricritical point, presumably at T approximately 16K and H approximately 0.3 T.