Magnetic properties and microstructure of Ho-Co sputtered films

An experimental study of perpendicular magnetic anisotropy and microstructure of Ho-Co sputtered films fabricated at various bias voltages has been carried out. The perpendicular magnetic anisotropy constant Ksub(u) is not much changed by negative bias voltage (-Vsub(b)). However, a detailed examination of the cross-sectional structure made by high voltage electron microscopy and using a ''micro-micro diffraction'' technique reveals a strong dependence of film structure on (-Vsub(b)). The films made at Vsub(b) = 0 consist of fine columns of 100 to 200A diameter surrounded by a network of less dense materials of about 30A thickness. With increasing (-Vsub(b)), a region near one side of film surface, giving rise to a spotty diffraction pattern, appears. With further increasing (-Vsub(b)), a highly porous region is found on one side of the film cross-section, but a columnar structure still exists on the other side. The present result implies that a columnar structure is responsible for the perpendicular magnetic anisotropy for films made at no bias voltage, but other mechanisms must be taken into account for higher bias voltages. (author)