Control of Surface Morphology and Magnetic Properties by Ion Bombardment in FePt Thin Films

Fe₄₉Pt₅₁ thin films with a thickness of 20 nm were deposited by conventional dc co-sputtering at substrate temperature of 400 and 500^°C before undergoing glow-discharge-induced ion bombardment at room temperature. The energy of the incident Ar ions was adjusted by applying a radio-frequency bias (V_b) in the range of 50 to 600 V. Significant abilities of ion bombardment in modifying both chemical ordering and surface morphology are demonstrated. With V_b in the range of 50 to 150 V, the bombardment smoothes the surface and enhances ordering by promoting surface diffusion. Bombarding at high V_b greater than 200 V evolves the surface morphology towards discontinuous island-like structure or rough pinhole topography and causes disordering by progressive etching. The magnetic properties can be tuned with the structural transformations by ion bombardment. The coercivity (H_c) can be increased from 0.57 to 0.75 MA/m by improving ordering for the films deposited at 400^°C. On the other hand, the disordering and mass loss may produce the magnetic softening and drastically reduced magnetization.