Temperature dependence of magnetic properties in epitaxial Cu/Ni/Cu/Si (111) measured by magneto-optical Kerr effect

We report on magneto-optical Kerr effect (MOKE) measurements performed in the range 4-300 K on five epitaxial Cu/Ni/Cu/Si (1 1 1) heterostructures, grown by UHV evaporation, with the Ni layer thickness d varying in the range between 30 and 10 Angstrom. In a previous work, we showed that, at room temperature, the magnetization lies preferentially in-plane for d greater than or equal to 30 Angstrom while it switches out-of-plane when 15 less than or equal to d less than or equal to 25 Angstrom. In this work, we show that on further reducing the film thickness the magnetization undergoes a second reorientation transition. For d = 10 Angstrom an in-plane magnetization is found with a coercive field which becomes negligible above 200 K. No orientation transition is observed as a function of temperature for any of the specimens analyzed. However, the estimated coercive field and the loop squareness decrease monotonically with increasing temperature. (C) 1999 Elsevier Science B.V. All rights reserved.