The temperature ͑T͒ dependence of the muon and 63 Cu nuclear spin-lattice relaxation rates 1 / T 1 in YbCu 4.4 Au 0.6 is reported over nearly four decades. It is shown that for T → 0 1/ T 1 diverges following the behavior predicted by the self-consistent renormalization ͑SCR͒ theory for a ferromagnetic quantum critical point. On the other hand, the static uniform susceptibility s is observed to diverge as T −2/3 and 1 / T 1 T ϰ s 2 , a behavior which is not accounted for by SCR theory. The application of a magnetic field H is observed to induce a crossover to a Fermi-liquid behavior and for T → 0 1/ T 1 is found to obey the scaling law 1Strongly correlated electron systems with competing interactions are known to show rather rich phase diagrams, with crossovers or phase transitions which depend on the relative magnitude of the competing energy scales. A paradigmatic example is represented by heavy-fermion intermetallic compounds, where a quantum phase transition between Fermi liquid ͑FL͒ and magnetic ground states is typically observed upon varying the single-ion Kondo coupling J and the density of states at the Fermi level D͑E F ͒. 1 The modification of these two parameters affects both the coherence temperature T ‫ء‬ , below which the f electrons delocalize and a FL behavior is observed, and the transition temperature to a magnetic long-range order, which is determined by Ruderman-Kittel-Kasuya-Yosida ͑RKKY͒ interaction. 2 At the quantum critical point ͑QCP͒ T ‫ء‬ → 0, the Fermi-liquid regime is never attained and a rather peculiar behavior of the response functions is observed down to T → 0, the so-called non-Fermi-liquid ͑NFL͒ regime. The QCP can be tuned by different parameters, such as the chemical composition, the pressure, and the magnetic field, which control the hybridization between f and s electron orbitals, i.e., J and D͑E F ͒. 3 In spite of the significant experimental efforts, an overall understanding of how the dynamical spin susceptibility behaves in the NFL regime on approaching the QCP and how it is affected by external parameters, such as the magnetic field, is still missing.YbCu 5−x Au x is a heavy-fermion intermetallic compound which has been studied in recent years mostly with techniques of macroscopic character, ranging from specific heat to magnetization and resistivity measurements. 4-6 On the basis of these experimental results a tentative phase diagram as a function of x has been outlined. The coherence temperature T ‫ء‬ , which for x = 0 was estimated to be around 5 K, vanishes around x Ӎ 0.4, where a quantum phase transition to a longrange magnetic order is expected. 4 Still, it has to be pointed out that the transition temperature to the magnetically ordered phase for x Ͼ 0.5 has been determined just from the change in slope in the resistivity vs temperature, 4 raising some doubts on the accuracy of its estimate. Moreover, a careful analysis of the chemical and structural properties of YbCu 5−x Au x solid solutions 7 has shown that homogeneous compounds with cubic AuBe 5 -type struc...

We have experimentally determined the magnitude of the in-plane magnetocrystalline anisotropy of monatomic Fe steps on the surface of nanopatterned Fe/ Ag͑001͒ films. The films have been nanopatterned by the ion-sculpting technique, in which grazing-incidence ion sputtering is exploited to induce the formation of nanometer-scale surface ripples oriented along the ion-beam direction. We quantitatively assessed the ripple morphology in order to determine the density of Fe monatomic steps parallel to the ripple ridges. By correlating the morphology with the measured uniaxial magnetic anisotropy, we obtained the strength of the magnetocrystalline anisotropy of Fe monatomic steps u mc = ͑6.5± 1.5͒ ϫ 10 −10 erg/ cm.

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The phase relations of the CeCo(9 + δ)Si(4 - δ) system have been studied by means of scanning electron microscopy, electron microprobe analysis and x-ray diffraction. Essentially single phase samples CeCo(9 + δ)Si(4 - δ) (structure-type LaFe(9)Si(4) with space group I4/mcm) are formed in a narrow composition range - 0.3 ≤ δ < 0.1, where stoichiometric CeCo(9)Si(4) exhibits full structural order in space group I4/mcm. The evolution of the ground state of correlated 3d and 4f electrons in the solid solution CeCo(9 + δ)Si(4 - δ) has been investigated by dc susceptibility, magnetization, specific heat and resistivity measurements. Stoichiometric CeCo(9)Si(4) exhibits paramagnetic Kondo lattice behaviour with a largely reduced Co 3d contribution to the magnetic susceptibility as compared to nearly ferromagnetic LaCo(9)Si(4). Nonetheless, very similar to the solid solution LaCo(9 + δ)Si(4 - δ), weak ferromagnetism is observed in CeCo(9 + δ)Si(4 - δ) for δ > 0 and is attributed to substitutional disorder at the Si-sublattice.