with Co be consistent with the dashed line in Fig. 1(b) and the solid line in Fig. 2(b). This means that either the metal is described by the Drude model but magnetic properties do not influence the Casimir pressure or, alternatively, the metal is described by the plasma model but there is the impact of magnetic properties on the pressure magnitude. The choice between these alternatives can be performed by the results of a second experiment using the same patterned Co-Au plate, but with the sphere coated with a nonmagnetic metal (Au). If the first alternative is correct, there is only a minor increase in the measured force (for about 10% at a = 0 . 5 µ m) when the sphere is moved from the Co to Au regions, as can be seen from the solid line in Fig. 5(a) and respective data for Au-Au interaction [14]. If the second alternative is correct, there would be a large increase in the measured force (for about 20% at a = 0 . 5 µ m) in the same movement (see the solid line in Fig. 6(a) and respective data for Au-Au plates [14]). Thus, the proposed measurements of the Casimir force between ferromagnetic metals allow one not only to confirm or exclude the influence of magnetic properties on dispersion interaction, but also to shed additional light on the choice between different theoretical approaches to the thermal Casimir force. Additional possibilities are suggested by the use of the test bodies made of ferromagnetic dielectrics. Here, in the measurement using the two plates made of ferromagnetic dielectrics, one can determine whether the magnetic properties influence the Casimir free energy and pressure (54% and 36% relative difference, respectively, at a = 0 . 5 µ m, as shown in Fig. 9). In doing so one does not require to make any assumptions concerning the use of the Drude or plasma models. Promising potentialities for the new experiments are also suggested by the magnetic phase transition in ferromagnetic metal at Curie temperature. According to our results, there are significant differences between the predictions of the Drude and plasma model approaches to the thermal Casimir force before and after the phase transition. G.L.K. and V.M.M. are grateful to the Institute for Theoretical Physics, Leipzig Uni- versity for kind hospitality. They are also grateful to G. Bimonte for useful discussions on the early stage of the work. This work was supported by Deutsche Forschungsgemeinschaft, Acknowledgments 26