Domain structures and temperature-dependent spin reorientation transitions in c-axis oriented Co–Cr thin films

Abstract

Highly c-axis oriented Co95Cr5 films with perpendicular anisotropy were grown epitaxially on Si (111), using an Ag seed layer, by physical vapor deposition. Films were characterized by x-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction, and Lorentz microscopy in a TEM. The following epitaxial relationship was confirmed: (111)Si∥(111)Ag∥(0001)CoCr;[2̄20]Si∥[2̄20]Ag∥[1̄100]CoCr. Magnetic domain structures of these films were observed as a function of thickness; t, in the range, 200 Å<t<700 Å using a wedge-shaped sample, and temperature-dependent measurements were carried out by in situ resistance heating. Thickness was measured locally by electron energy loss spectroscopy. At room temperature, below a critical thickness, tc≈300 Å, the magnetization was found to be effectively in-plane of the film, and above tc a regular, stripe-like domain pattern with a significant, alternating in sign, perpendicular component was observed. The spin reorientation transitions of the stripe domains to the in-plane magnetization were studied dynamically by observing the domains as a function of temperature by in situ heating up to 350 °C. The critical transition thickness, tc, which is a function of Ku and magnetostatic energy, was found to increase with increasing temperature. The stripe-domain period, L observed at room temperature was found to increase gradually with thickness; L=90 nm at t=300 Å, and L=110 nm at t=700 Å.