Domain Structures and Temperature-Dependent Spin Reorientation Transitions in c-Axis Oriented Co–Cr Thin Films

Highly c -axis oriented Co 95 Cr 5 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 ; [220] Si ‖ [220] Ag ‖[1100] 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, t c ≈ 300 Å, the magnetization was found to be effectively inplane of the film, and above t c 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 inplane 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, t c , which is a function of K u 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.