Nanoscale physical microstructure and micromagnetic behaviour of CoIr film with negative anisotropy

The physical and magnetic structure of hcp-CoIr(10 nm)/Ru(5 nm) has been systematically characterized using transmission electron microscopy. The film was observed to be polycrystalline with a mean grain size of 15.7 +/- 1.1 nm. Additionally, diffraction analysis in the TEM confirmed the presence of a [0 0 0 1] texture normal to the film plane resulting from a Ru seed layer. Lorentz microscopy observation with in situ magnetizing experiments showed that the film possessed a weak-anisotropy easy axis with considerable dispersion of magnetic ripple and domain wall nucleation over a negative field of 25 Oe. Magnetization reversal on the hard axis shows a non-coherent rotation of magnetic moments from easy axis to hard axis denoted by a non-uniform nucleation of low-angle walls. Dispersion of magnetization ripple is in agreement with classical ripple theory. Generally the magnetization reversal was complete by 30 Oe; however, some small regions remained which were not fully reversed with associated 360 degrees domain walls. These appeared to be strongly pinned locally and required much larger fields to eliminate them.