MAGNETIZATION REVERSAL OF GD(0001) THIN-FILMS - TBIS BUTTERFLIES AND MOKE BUTTERFLIES IN UHV

We present an in situ butterfly study of the in plane magnetization re versal of epitaxial hcp Gd(0001) thin films grown on bcc W(110) at T(s ) = 450-degrees-C in ultrahigh vacuum (UHV). Two UHV-compatible techni ques, viz., transverse biased initial susceptibility (TBIS) and magnet o-optic Kerr effect (MOKE) are used to in situ record the so-called bu tterfly loops well below the bulk Curie temperature (T(cb) is-approxim ately-equal-to 293 K). The derivative character of these loops allows one to determine the in-plane coercive field (H(c)). Hcp Gd(0001) thin films, 40 and 80 nm thick, are found to be magnetically soft with in- plane H(c) < 30 Oe for T = 109, 132 and 230 K. A low value of H(c) (is -approximately-equal-to 5.8 Oe) is observed at T = 230 K, this tempera ture being close to the onset of spin-reorientation in bulk gadolinium (T(SR)b is-approximately-equal-to 245 K). Also at T = 230 K, a value of in-plane anisotropy field H(k) is-approximately-equal-to 27 Oe is d educed. We distinguish two cases, both of them being measured in the l ow-applied-field regime where para-processes are negligible: (i) the G d(0001) thin films when biased perpendicularly to the basal plane exhi bit an anhysteretic behavior and (ii) as soon as the films are biased in the basal plane, the bias-field dependence of both TBIS and MOKE si gnals becomes hysteretic and the magnetization does reverse. The anhys teretic behavior might be related to the recently observed effect of s urface spin canting. In this article, we focus mainly on the case of G d(0001) thin films biased in the film plane. From the so-called Frolic h-Kennelly plots, it is concluded that thinner Gd(0001) films show sma ller hysteresis losses accompanying the in-plane magnetization reversa l. A comprehensive historical review of the butterfly methods is also given in this paper.