Noncollinear amplitude-modulated magnetic order in Gd compounds

In the present work a model within the mean-field theory is developed in order to analyze the specific heat of magnetically ordered systems. This model allows to draw conclusions about the type of magnetic structure from the specific heat near the magnetic transition. The known description of collinear amplitude-modulated and equal-moment magnetism has been extended to account for noncollinear amplitude-modulated (NCAM) antiferromagnetic order by introducing an anisotropic exchange interaction. Experimental evidence for NCAM order is expected from measurements of the specific-heat anomaly at the ordering temperature and from magnetic scattering experiments. The specific heat of GdCu₂ was measured and analyzed within the model and a good agreement is reached. Furthermore, the specific heat of other noncollinear Gd antiferromagnets near the ordering temperature has been calculated and is compared to available experimental data.