Powder hematite transformation induced by swift heavy ion irradiation with fluence threshold observation

57Fe transmission M¨ossbauer (TMS) spectroscopy and powder X-ray diffractometry (XRD), as well as scanning electron microscopy (SEM-EDX) measurements were used to study the effect of swift heavy ion irradiation on powdered hematite mixed with epoxy resin. TMS, XRD and EDX of the samples indicated no significant changes neither in the crystal structure nor in the composition of hematite irradiated with 148 MeV Xe ions with a fluence of 1 Å~ 1013 cm􀀀 2 as compared to those of non-irradiated ones. However, about a quarter of the total iron content of the hematite detected by TMS was converted to wüstite and to magnetite superparamagnetic at room temperature upon irradiation with a fluence of 5 Å~ 1013 cm􀀀 2. The presence of wüstite was evidenced by XRD in agreement with TMS measurements. Temperature dependence of the hematite TMS measurements indicated a significant change in the Morin transition after irradiation with a fluence of 5 Å~ 1013 cm􀀀 2. The results are discussed in terms of the defects produced by irradiation and