In this paper the transformation of the partial time inversion is discussed. For magnetic dimers it is shown that at partial time inversion the change of sign for the exchange integral takes place. This allows transforming the antiferromagnetic type of ordering into the ferromagnetic one and vice versa. Specifically, for magnetic dimers containing equivalent ions with S = 1/2, the partial time inversion transformation leads to spin level inversion. The possible 3d-3d and 4f-4f dimer clusters with antiferro- and ferromagnetic types of ordering are indicated. The electron paramagnetic resonance data for 3d-3d dimers proving the suggested statements are presented.