Phase diagram and magnetic structures of CeSb

Among cerium pnictides, the compound CeSb exhibits the most complex behavior. The magnetic structures of the numerous observed phases have been determined. The magnetic field has been applied along a fourfold axis of the rock salt structure. For all the phases the order consists of square-wave structures characterized by a propagation vector →k=(0, 0, k) of value commensurate with the crystallographic cell and by a strong anisotropy confining the moments along the k vector. All the structures can be generated by a periodic stacking of zero magnetized planes P and ferromagnetic planes with a magnetization parallel M↑ or antiparallel M_↓ to the applied field. Three types of structures can be distinguished: (a) at low temperature only M↑ and M_↓ planes exist, the structures k=4/7 (++--++-), k=2/3 (++-), and $k=0$ are successively observed when the field is increased. (b) at high temperature and low field M↑, M_↓, and P planes coexist leading to an "antiferroparamagnetic order." (c) at high temperature and high field only M↑ and P planes exists defining a ferroparamagnetic order. The phase diagram feature can be understood by a simple thermodynamic analysis considering an entropy S₀=kln2 for paramagnetic planes and a moment of 2.1 μB/Ce atom for magnetized planes.