THE CURIE-TEMPERATURE IN ULTRATHIN NI CU(001) FILMS DETERMINED BY AC SUSCEPTIBILITY AND MOKE/

Results are presented on the a.c. susceptibility chi(ac) of single lay ers of Ni on Cu(001) measured in situ in UHV by mutual inductance and an ac Kerr-effect setup. The temperature dependence of chi(ac) for 3-1 0 ML Ni/Cu(001) is shown. The thickness dependence of the Curie temper ature T-c is directly obtained from the temperature T-max at the maxim um of chi(ac) for in-plane magnetized films (d<7 ML). Perpendicularly magnetized films (d>7ML) form domains 10-20 K below T-c. Therefore, T- max of these samples corresponds to a critical temperature for domain formation and not to T-c. This is reflected in a change of slope of th e T-c(d) curve, which will be discussed. By heating as-deposited films d approximate to 8 ML up to 400 K, strong changes in chi(ac) and hyst eresis loops are observed. (C) 1998 Elsevier Science B.V. All rights r eserved.