Hard magnetic nanocomposites SmCo 5 /Fe x ͑x =0-2.9͒ are synthesized by a simultaneous calcium reduction of Sm-CoO and Fe 3 O 4 nanoparticles. The composites consist of nanostructured SmCo 5 and Fe with their average grain sizes at 29 and 8 nm, respectively. The magnetic properties of the composites can be tuned by controlling Fe composition. SmCo 5 /Fe 1.5 shows an enhanced remanent magnetization at 56 emu/ g ͑45 emu/ g for SmCo 5 ͒. The largest coercivity value of 11.6 kOe is achieved with SmCo 5 /Fe 0.23. The synthesis represents a general process toward SmCo-based exchange-spring nanocomposites for high performance permanent magnet applications.

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