Crystallinity and magnetic property of binary Fe-As compounds grown on GaAs(001) substrates by molecular beam epitaxy are described. At the substrate temperature of T-s=300 degrees C or lower, the growth occurs in the form of polycrystalline diamagnetic FeAs2, whereas, at T-s=400-500 degrees C, the growth of single-crystalline FeAs or Fe2As takes place depending on the relative amount of an As beam flux. At T-s=600 degrees C, formation of polycrystalline FeAs with Fe-Ga-As ternary compounds starts to take place. Using these binary samples, magnetic susceptibility of FeAs2 and FeAs are extracted and compared with the bulk data. It is also revealed that these binaries do not exhibit photo-enhanced magnetization at room temperature. (c) 2007 Elsevier B.V. All rights reserved.