The first-order phase transition from the antiferromagnetic to the ferromagnetic phase in equiatomic FeRh alloys has attracted interest due to its potential applications in magnetic recording and memory technologies. The transition occurs slightly above room temperature, around 350 K, and exhibits a thermal hysteresis with a width of approximately 20 K, within which the antiferromagnetic and ferromagnetic phases coexist. The high tunability of FeRh, together with the pronounced changes in magnetization and electrical resistivity accompanying the phase transition, makes this material particularly attractive.

However, practical operation of potential magnetic storage devices based on common FeRh films would require external heating, which reduces energy efficiency. In addition, the relatively narrow phase-coexistence interval limits the thermal stability of the device. For technological applications, it is therefore desirable to decrease the transition temperature toward 300 K and to substantially broaden the thermal hysteresis.

In this work, we investigate the tunability of the phase transition in FeRh thin films by optimizing deposition conditions and by subsequent irradiation with C⁺ and H⁺ ions with an energy of 20 keV. The study focuses on controlling the transition temperature Tt and the hysteresis width ΔT through variations in film thickness, substrate type, ion dose, and irradiation temperature.

The results show that 20-nm-thick FeRh films grown on Al₂O₃ exhibit, already in the as-grown state, a thermal hysteresis 59 K wide centered near room temperature. Irradiation with C⁺ ions leads to a pronounced broadening of the transition, reaching up to 84 K, accompanied by a significant reduction of Tt down to 227 K. Furthermore, ion irradiation combined with annealing enables the thermal hysteresis of samples with initially high Tt to be shifted close to room temperature, while maintaining hysteresis widths of around 50 K.