We have used scanning-tunneling microscopy to study the structure of Gd thin films grown on W͑110͒ and its relationship to the magnetic properties. The film morphology is examined for different coverages and for two different post-deposition annealing temperatures ͑530 and 710 K͒, permitting predictions of the in-plane demagnetization factor and the Curie temperature that are in excellent agreement with prior ac magneticsusceptibility measurements. The first monolayer of Gd is also found to grow in a (7ϫ14) lateral superstructure, giving rise to in-plane lattice distortions of ϳ1% as compared to the values of bulk Gd.Over the last ten years, a number of studies of the magnetic properties of thin films of Gd grown epitaxially on W͑110͒ single-crystal substrates has been performed. [1][2][3][4][5][6][7][8][9][10][11][12] This system of a 4 f ferromagnetic metal deposited on a nonmagnetic transition metal has provided much interesting data, including, for example, indications of an elevated surface Curie temperature. 1,2 Although particular growth modes and film morphologies for this system have been inferred indirectly from techniques such as Auger electron spectroscopy ͑AES͒ and low-energy electron diffraction ͑LEED͒, 1,13 no direct observations of surface morphology using scanning-tunneling microscopy ͑STM͒ have been made. In this paper, we study the effects of coverage and annealing temperature on the morphology of such Gd films with STM. These results yield a more quantitative understanding of the structure-magnetism relationships for this prototypical epitaxial ferromagnet and also reveal a new superstructure for the first monolayer.Some important prior observations for Gd/W͑110͒ are as follows. Weller et al. 1 proposed based upon AES measurements that Gd films deposited on W͑110͒ substrates held at between 723 and 773 K grow via the Stranski-Krastanov ͑SK͒ mode ͓three-dimensional ͑3D͒ island growth on top of one or more epitaxial monolayers͔. This same work used spin-polarized LEED and the magneto-optic Kerr effect ͑MOKE͒ to determine that the surface Curie temperature (T Cs ) was higher than that of the bulk (T Cb ) by 22 K. A later study by Tang et al. 2 employed spin-polarized secondary electron emission spectroscopy and spin-polarized photoelectron spectroscopy and concluded that T Cs was 60 K higher than T Cb , that there was a ferromagnetic alignment of the in-plane component of the surface and bulk moments, and that the surface magnetization appeared to be canted. Gd is thus one of only two ferromagnetic materials for which T Cs has been observed to be greater than T Cb , with the other being Tb͑001͒, as studied by Rau et al. using electron capture by deuterons 14 Kolaczkiewicz et al. 13 further investigated the growth modes and surface structures of Gd/W͑110͒ utilizing LEED and AES. From breaks in AES intensities as a function of coverage, ⌰, they inferred that, for lower coverages ͓⌰Ͻ3 monolayers ͑ML͔͒ and when deposited at room temperature, Gd grows in the Frank-Van der Merwe ͑FM͒ mode ͑smooth, lay...
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