Magnetically dilute metallic glasses. II. 4\u3ci\u3ef\u3c/i\u3e moments

Magnetic-susceptibility and high-field magnetization measurements are presented for amorphous Zr40Cu600-xMx (M denoting Gd and Tb), with x ranging from zero to ten. Effective moments of magnetic solutes were determined by fitting susceptibility data to the Curie-Weiss expression. The moments of Gd and Tb are very close to those expected for trivalent ions and the paramagnetic Weiss temperatures are positive. Saturation did not occur in any of the samples, even at 80 kOe and 1.3 K; however, the alloys containing Gd approached normalized magnetization values of unity. High-field hysteresis loops were used to obtain the temperature dependence of the coercive fields Hc and to determine ordering temperatures, defined as those temperatures for which Hc vanishes. The zero-field susceptibility for both the Gd and Tb alloys shows sharp peaks at low temperatures. The magnetically ordered state of the Gd alloys is characterized as spin-glass-like; that is, the spins are frozen in random directions and there are both ferromagnetic and antiferromagnetic exchange interactions, with the former dominant. The Tb alloys also have low-temperature magnetic states characterized as spin-glass-like in this sense. However, in the Tb alloys, the presence of local random anisotropy affects the high-field magnetization considerably. Attempts to fit the high-field magnetization of the Tb alloys to the local-random-anisotropy theory of Harris et al. are described

Ab-initio density functional studies of stepped TaC surfaces

We report on density functional total energy calculations of the step formation and interaction energies for vicinal TaC(001) surfaces. Our calculations show that double and triple-height steps are favored over single-height steps for a given vicinal orientation, which is in agreement with recent experimental observations. We provide a description of steps in terms of atomic displacements and charge localization and predict an experimentally observable rumpled structure of the step-edges, where the Ta atoms undergo larger displacements compared to the C atoms.Comment: 4 pages, 4 figure

Critical properties of random anisotropy magnets

The problem of critical behaviour of three dimensional random anisotropy magnets, which constitute a wide class of disordered magnets is considered. Previous results obtained in experiments, by Monte Carlo simulations and within different theoretical approaches give evidence for a second order phase transition for anisotropic distributions of the local anisotropy axes, while for the case of isotropic distribution such transition is absent. This outcome is described by renormalization group in its field theoretical variant on the basis of the random anisotropy model. Considerable attention is paid to the investigation of the effective critical behaviour which explains the observation of different behaviour in the same universality class.Comment: 41 pages, 10 figure

Oxygen chemisorption on Cu(110): A model for the c(6×2) structure

From an interplay between scanning tunneling microscopy, surface x-ray-diffraction experiments, and theoretical predictions, an unequivocal structural model for the Cu(110)-c(6×2)O surface reconstruction is derived with ten Cu atoms within the c(6×2) unit cell, two of which form a Cu superstructure. A general picture evolves in which the present as well as the Cu(110)-(2×1)O and the Cu(100)-(2 √2 × √2 )R45°O reconstructions are stabilized by Cu-O-Cu chains directed along the [001] direction. The nucleation and growth of the c(6×2) structure occur preferentially at steps