Rare-earth transition-metal (R-TM) alloys show superior permanent magnetic properties in the bulk, but the synthesis and application of R-TM nanoparticles remains a challenge due to the requirement of high-temperature annealing above about 800°C for alloy formation and subsequent crystalline ordering. Here we report a single-step method to produce highly ordered R-TM nanoparticles such as YCo 5 and SmCo 5, without high-temperature thermal annealing by employing a cluster-deposition system, and we investigate their structural and magnetic properties. Nanoparticles of size d ≤ 10 nm are monodispersed (σ/d≈ 0.15) and have H c values at T = 300 K of 8.0 and 4.5 kOe for YCo 5 and SmCo 5, respectively. Alignment of the easy axes is performed via a field applied to the clusters before deposition. These processing steps are highly desirable to create and assemble R-TM nanoparticle composites for future permanent-magnet applications.