The synthesis of a new BCT Fe phase was performed in Fe/Ir(100) superlattices grown by MBE. Magnetic properties of ⁵⁷Fe/Ir(100) superlattices with 4 ml Fe and variable Ir thickness (2–30 Å) are investigated by ⁵⁷Fe conversion electron Mössbauer spectroscopy in the 4.2–300 K temperature range. Two spectral components are evidence, related, respectively, to Fe atoms involved in the central part of the iron layers and at the interface between iron and iridium layers. The appearance of a high magnetic hyperfine splitting in the iron BCT structure above a volume threshold of 12 ų is evidenced. Marked differences are observed between the mean magnetic properties and the local ones suggesting strong relaxation effects.