Canted Magnetic Moments at The Gd(0001) Surface
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CANTED MAGNETIC MOMENTS AT THE Gd(0001) SURFACE Dongqi Li, Jiandi Zhang, and P. A. Dowben Department of Physics, Syracuse University, Syracuse, NY 13244 K. Garrison, and P. D. Johnson Physics Department, Brookhaven National Laboratory, Upton, NY 11973 H.Tang*, T.G.Walker, and H.Hopster
Department of Physics, University of California, Irvine, CA 92717 J.C.Scott, D. Weller, and D. P. Pappast
IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120
ABSTRACT With spin polarized electron spectroscopies, we have investigated ordered (d(0001) films deposited on W(110). The photoemission features of the gadolinium 5d surface state, the 4f levels, and the background exhibit considerable spin polarization along the same direction in the plane of the film, indicative of ferromagnetic coupling between the surface and the bulk. The 4f spin polarized photoemission data provides strong evidence that the surface 4f polarization differs from the bulk 4f polarization for Gd(0001). Our temperature dependent measurements with spin polarized secondary electron spectroscopy conclusively establishes that the surface of clean Gd(0001) possesses a perpendicular polarization component which persists to an enhanced surface Curie temperature. Small amounts of contamination at the surface result in the disappearance of the perpendicular component and, therefore, a more perfect ferromagnetic coupling between the surface and the bulk. INTRODUCTION The issues of surface magnetic anisotropy and the magnetic coupling between the surface and the bulk have attracted considerable attention. The Gd(0001) surface appears to exhibit enhanced magnetic order, i.e., higher Curie temperature at the surface than in the bulk [1]. It is seen to be able to maintain an in-plane remanent magnetization [1, 2, 3,4], although there is indication that an perpendicular anisotropy exists for ultrathin Gd films[4]. Calculations [5] supported the altered exchange coupling in the surface layer, and the postulate put forward earlier on the basis of experiment [1] that the surface is antiferromagnetically coupled with the bulk. In this paper, we provide evidence that the surface is not antiferromagnetically coupled with the bulk but rather an imperfect ferromagnetic coupling exists between the surface and the bulk as a result of a sizable perpendicular polarization of the surface layer, consistent with earlier work [3, 6, 7]. This effect undoubtedly results in phenomena consistent with the earlier experiment [I] but challenges the simpler models of perfect antiferromagnetic [1, 5] or perfect ferromagnetic [8] coupling between the surface and the bulk. Our recent photoemission studies [9, 10, 11] of the Gd(0001) band structure have demonstrated the existence of a surface state at r consistent with the theoretical band structure[5]. The surface state is well localized at the surfacefll, 12], and is therefore a unique probe of the surface magnetic order without requiring the complex task of separating surface and bulk signals. In addition, the temperature dependence o
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