CORRELATION BETWEEN DYNAMIC MAGNETIC HYSTERESIS LOOPS AND NANOSCALE ROUGHNESS OF ULTRATHIN CO FILMS

Ultrathin Co films were epitaxially grown on a Cu(001) surface with di fferent initial roughness created by Ar ion sputtering. The roughness of the Cu substrate and the Co film were characterized by high resolut ion low energy electron diffraction. The measured angular profiles wer e compared with a diffraction theory for rough surfaces and the roughn ess parameters were extracted quantitatively. Magnetic hysteresis loop s of these characterized films were measured by surface magneto-optic Kerr effect. The hysteresis loop shape and loop area can be related to the nanoscale roughness in the Co films. For the roughest film with i nterface width approximate to 1.2t, where t is the single atomic step height, the magnetization is reduced several fold compared with that o f smooth films with interface width approximate to 0.5t. Also, the coe rcivity in the roughest film is the highest and there exists a wide ra nge of nucleation centers and coercive fields for magnetic domain reve rsals. These are related to the high step density in the rough substra te as the pinning centers. The hysteresis loop changes its shape and a rea under a sinusoidal external magnetic field as functions of frequen cy and field amplitude for all films. For the smooth films in the low frequency and low field regimes the loop area shows a 2/3 power law sc aling behavior. The 2/3 value of scaling exponents are consistent with the prediction of a dynamic mean field theory with a double-well ener gy barrier. For a film with the same interface width but different ste p density and lateral correlation length the scaling exponents deviate from 2/3 value drastically. (C) 1996 American Vacuum Society.