In this work, the structural and magnetic properties of rapidly-cooled alloys Fe60Co10Y5+xZr5-xB20 were investigated. The chemical composition of the alloy and manufacturing parameters were selected to obtain a partially-crystallised structure. The tested nanocrystalline alloys were produced by injection of each liquid alloy into a copper mould. The structure of each alloy was investigated using X-ray diffraction. The diffractogram analysis was performed using the specialist Match! software. The magnetic properties of the alloys were determined on the basis of measurements that were carried out using a vibrating sample magnetometer. The study showed that it is possible, using a single-stage process, to produce an alloy with a nanocrystalline structure containing a significant proportion of an amorphous matrix. It was found that varying the proportions of Y and Zr promoted the creation of different crystalline phases. This fact was related to the physical properties of the elements: the higher value of the negative heat of mixing for Zr with the other alloying components, compared with Y. In the case of the alloy with the higher content of Y, a phase was identified which exhibited so-called “hard-magnetic” properties. The formation of this phase results in a different distribution of Fe atoms, as indicated by a higher value of saturation magnetisation and lower value of the spin-wave stiffness parameter.