Magnetization reorientation in Ni (111) ultrathin films studied by low-temperature hysteresis measurements

Surface magneto-optical Kerr effect (SMOKE) magnetometry in the temperature range 10-300 K was exploited to investigate the magnetic properties of hig h-quality Cu/Ni/Cu/Si(1 1 1) epitaxial heterostructures with thickness of t he Ni layer, d(Ni), between 10 and 60 Angstrom. For a fixed temperature, th e equilibrium direction of the magnetization is parallel or perpendicular t o the film surface, depending on the Ni thickness, because of the competiti on among shape anisotropy, magnetoelastic anisotropy and interface anisotro py. No reorientation of the magnetization could be observed as a function o f temperature, for any of the specimens analyzed, while a large variation o f the loop squareness and coercivity was found, This last variation has bee n qualitatively explained using a theoretical model based on a Green's func tion technique, valid for a monodomain film with a coherent rotation of the magnetization. (C) 2000 Elsevier Science B.V. All rights reserved.