Permanent magnets (PM) play an important role in modern devices and enabling technologies as they allow for storing, delivering and converting energy. In terms of volume, Sr- and Ba- ferrites are one of the world’s most-used permanent magnetic materials. Despite the overwhelming superiority in performance of rare-earth magnets, the harmful environmental impact of their production, uneven distribution and a questionable supply due to geopolitical fluctuations force us to look for alternatives. One such solution emerges from the group of hexagonal ferrites since they do not contain critical raw materials. Sintering by Intense Thermal Radiation (SITR) uses the Joule heating effect to generate heat in the heating body that is transferred to the sample via thermal radiation and enables the necessary energy for densifying the ceramic particles. This is a novel approach to sintering hexagonal strontium ferrite. In this study, we have focused on the phase evolution of strontium hexaferrite during SITR. Sintering was performed in an SPS device with a modified graphite model and in a vacuum atmosphere. Several sintering parameters were tested, among which the sintering temperature and retention time at that temperature had the largest effect on the magnetic properties of sintered pieces. According to the Sr-ferrite phase diagram, the SrFe₁₂O₁₉ is supposed to be stable at least up to 1350 °C. Nevertheless, the phase composition analysis has shown that the decomposition of strontium hexaferrite occurs during SITR already at sintering temperatures as low as 1100 °C. The scanning electron microscopy analysis coupled with energy dispersive spectroscopy (SEM-EDS) suggested that the material undergoes a segregation process in which strontium-rich and poor phases are being formed. To better understand the SrFe₁₂O₁₉ phase decomposition in the given sintering environment also, a high-temperature X-ray diffraction analysis of SrFe₁₂O₁₉ with the addition of 10 wt% of graphite powder was performed. Analysis revealed that in such a highly exaggerated reductive environment, the reduction of SrFe₁₂O₁₉ starts already between 260 and 600 °C and that at 1100 °C, only pure iron and Sr₄Fe₃O_10-d can be identified. This study has revealed that although SITR is a very promising consolidation technique, one has to be very careful when selecting a sintering environment (material of the die, sintering atmosphere). In the future, sintering dies made of other materials (such as tungsten carbide) will be used for SITR of Sr-ferrite magnets.