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 t he range 4-300 K on five epitaxial Cu/Ni/Cu/Si (1 1 1) heterostructures, gr own 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 tem perature, 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 o r 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 orien tation transition is observed as a function of temperature for any of the s pecimens analyzed. However, the estimated coercive field and the loop squar eness decrease monotonically with increasing temperature. (C) 1999 Elsevier Science B.V. All rights reserved.