Previous polarized electron experiments and recent ab initio calculations suggest that the surface layer magnetic moments of Gd(0001) are antiferromagnetieally coupled to the bulk magnetic moments.Spin-polarized photoemission data are presented which show that the spin polarization of the magnetic surface state and the surface 4f states of Gd(OOOI ) are coupled ferromagnetically to the bulk magnetic moment.PACS numbers: 75. 10.Lp, 75.50.Cc, 79.60.Cn Gadolinium has been considered an important prototype material for testing local-spin-density approximation (LSDA) calculations on rare-earth metals where localized 4f electrons, exchange, and relativistic (spin-orbit) eA'ects play important roles [1][2][3][4][5][6]. In the rare earths, the LSDA appears to overestimate the itineracy of 4f levels leading to predictions of structural, electronic, and magnetic properties often in relatively poor agreement with experiment, a few exceptions being La and Lu which have either an empty or filled 4f shell. Calculations for bulk Gd typically yield lattice constants which vary by a factor of 2 beyond limits considered appropriate for systems where the LSDA is judged accurate. LSDA calculations of band structure and magnetic properties are often in reasonable agreement with experiment. Recent self-consistent calculations for bulk Gd have yielded a conduction-band magnetic moment per atom (-0. 57pti) in good agreement with measurements (-0.63), and an average 5d-band exchange splitting (-0.6 eV) in reasonable agreement with recent angle-resolved photoemission measurements [7] of the A2 band dispersion and exchange splitting. However, the binding energies and dispersion of the h2 bands obtained from existing LSDA calculations do not agree with experimental results (-50% discrepancies), suggesting either inaccuracies in the calculations, inliuence of surface eA'ects due to short electron mean free paths [8], or strong many-body eITects [9] in the photoemission similar to those apparent in Ni. Surface properties of Gd(0001) are of intrinsic interest and also provide an additional means of testing LSDA calculations. Previous surface-sensitive probes of magnetism applied to Gd(0001) have established novel behavior. Spin-polarized low-energy electron-diA'raction (SPLEED) and magneto-optic Kerr eAect (MOKE) measurements [10] of single-crystal Gd(0001) surfaces [11] prepared on W(110) confirmed the existence of enhanced surface ferromagnetic order at temperatures up to 310 K ( -20 K above the bulk Curie temperature Tcb =293 K). These results, along with spin-polarized photoemission experiments [10] that probed bulk and surface 4f excitations, were interpreted as indicating antiferromagnetic coupling between the surface 4f spins and those of the underlying ferromagnetic bulk. Recent ab initio calculations [12] have examined the structural, electronic, and magnetic properties of Gd (0001), taking into account the total system energy.Several important results were obtained that can be directly compared with experimental results: First, th...