The aim of this project is to produce a prototype magnet in order to demonstrate the feasibility of a new generation of compact, and therefore less expensive, medical gantries for cancer particle therapy. The study on this magnet was tailored to particle-therapy machines designed by the TERA Foundation for cancer treatment. The principal innovation is the use of an iron cobalt (FeCo) alloy to build a laminated yoke. FeCo is a soft magnetic alloy showing a linear magnetic behaviour up to a saturation field of 2.35 T, about 0.7 T higher than for a standard FeSi alloy. This allows for the construction of a magnet 30% lighter than a conventional one, which in addition provides excellent dynamic characteristics thanks to the high electrical resistivity of this alloy.