This study discusses the effects of a CrPt3 alloy underlayer on the magnetic properties and microstructure of FePt films. The L1(2) CrPt3 phase was chemical long-range ordered at a temperature above 600 degrees C, and the 120-nm thick CrPt3 film annealed at 800 degrees C, resulting in ferrimagnetic behavior. The long-range ordered CrPt3 underlayer slightly increased the ordering of the L1(0) FePt film, as evidenced by the individual L1(2) CrPt3 and L1(0) FePt (0 0 1) superlattice peaks. An X-ray slow scan of the [FePt/CrPt3(T degrees C)](400 degrees c) bilayer shows that the integrated intensity of the L1(0) FePt (0 0 1) peaks was higher on the long-range order L1(2)-type CrPt3 (T= 600,800) underlayer and lower on the partial short-range order L1(2) and A(1) -types CrPt3 (T= 400) underlayer. However, optimal magnetic properties were obtained in the [FePt/CrPt3(400 degrees C)](400 degrees c) bilayer. When a FePt film is deposited on a ferrimagnetic CrPt3(800 C) underlayer, the resulting bilayer shows isotropic magnetic hysteresis loops and cannot be saturated at 1.8T. Atomic force microscopy (AFM) and transition electron microscopy (TEM) show that the L1(2) CrPt3(800 degrees C) underlayer exhibits coarse surface roughness and plate-like grains, respectively. From TEM images, all the FePt grains were isolated uniformly by CrPt3 matrix. (C) 2010 Elsevier B.V. All rights reserved.