1,114 research outputs found
Magnetic Properties of a-Si films doped with rare-earth elements
Amorphous silicon films doped with Y, La, Gd, Er, and Lu rare-earth elements
(a-Si:RE) have been prepared by co-sputtering and studied by means of electron
spin resonance (ESR), dc-magnetization, ion beam analysis, optical
transmission, and Raman spectroscopy. For comparison the magnetic properties of
laser-crystallized and hydrogenated a-Si:RE films were also studied. It was
found that the rare-earth species are incorporated in the a-Si:RE films in the
RE3+ form and that the RE-doping depletes the neutral dangling bonds (D0)
density. The reduction of D0 density is significantly larger for the magnetic
REs (Gd3+ and Er3+) than for the non-magnetic ones (Y3+, La3+, Lu3+). These
results are interpreted in terms of a strong exchange-like interaction, J RE-DB
SRE SDB, between the spin of the magnetic REs and that of the D0. All our
Gd-doped Si films showed basically the same broad ESR Gd3+ resonance (DHpp ~
850 Oe) at g ~ 2.01, suggesting the formation of a rather stable RE-Si complex
in these films.Comment: 15 pages, 7 figure
Dipolar interaction and incoherent quantum tunneling: a Monte Carlo study of magnetic relaxation
We study the magnetic relaxation of a system of localized spins interacting
through weak dipole interactions, at a temperature large with respect to the
ordering temperature but low with respect to the crystal field level splitting.
The relaxation results from quantum spin tunneling but is only allowed on sites
where the dipole field is very small. At low times, the magnetization decrease
is proportional to as predicted by Prokofiev and Stamp, and at long
times the relaxation can be described as an extension of a relaxed zone. The
results can be directly compared with very recent experimental data on Fe_8
molecular clusters.Comment: 9 pages, 11 figures; accepted for publication on Eur. Phys. J.
CHITRALINA UNDULATA GEN. N. SP. N. (FORAMINIFERIDA) FROM THE LATE PERMIAN OF KARAKORUM (PAKISTAN)
Chitralina undulata gen. n. sp. n. (Foraminiferida) has been found for the first time in the Permian successions of Karakorum (Pakistan). Biostratigraphic analysis based on fusulinids, brachiopods, conodonts and small foraminifers pointed out that Chitralina undulata gen. n. sp. n. occurs from the Kubergandian to the Late Murgabian-Midian. Morphologically, Chitralina undulata gen. n. sp. n., is comparable to Rectostipulina quadrata Jenny-Deshusses, 1985, differing from it by means of the thickness and composition of the test and for the presence of marked longitudinal costae. The stratigraphic range of Rectostipulina quadrata spans the Midian-Dorashamian time-interval. The new genus Chitralina is very similar to the Permian genus Giraliarella Crespin, differing from it by means of the absence of transverse growth constrictions. The new family Chitralinidae fam. n., is also described herein
Unified continuum approach to crystal surface morphological relaxation
A continuum theory is used to predict scaling laws for the morphological
relaxation of crystal surfaces in two independent space dimensions. The goal is
to unify previously disconnected experimental observations of decaying surface
profiles. The continuum description is derived from the motion of interacting
atomic steps. For isotropic diffusion of adatoms across each terrace, induced
adatom fluxes transverse and parallel to step edges obey different laws,
yielding a tensor mobility for the continuum surface flux. The partial
differential equation (PDE) for the height profile expresses an interplay of
step energetics and kinetics, and aspect ratio of surface topography that
plausibly unifies observations of decaying bidirectional surface corrugations.
The PDE reduces to known evolution equations for axisymmetric mounds and
one-dimensional periodic corrugations.Comment: 5 pages, 1 figur
GLOBIGAETANIA ANGULATA GEN. N. SP. N. (GLOBIVALVULININAE, FORAMINIFERA) FROM THE WORDIAN (MIDDLE PERMIAN) OF NW IRAN
A new small biseriamminoid foraminifer, Globigaetania angulata gen. n. sp. n., is here described from the Wordian of a Permian–Triassic sedimentary succession of NW Iran (Zal and Poldasht stratigraphic sections). The new taxon, dedicated to Prof. Maurizio Gaetani, is characterised by peculiar morphology, coiling, and structures that are characteristic of the subfamily Globivalvulininae Reitlinger, 1950, family Globivalvulinidae Reitlinger, 1950, superfamily Biseriamminoidea Chernysheva, 1941. The introduction of the new taxon contributes to the knowledge of the systematics and evolution of the Palaeozoic biserial microgranular foraminifera
Surface magnetic canting in a ferromagnet
The surface magnetic canting (SMC) of a semi-infinite film with ferromagnetic
exchange interaction and competing bulk and surface anisotropies is
investigated via a nonlinear mapping formulation of mean-field theory
previously developed by our group [L. Trallori et al., Int. J. Mod. Phys. B 10,
1935-1988 (1996)], and extended to the case where an external magnetic field is
applied to the system. When the field H is parallel to the film plane, the
condition for SMC is found to be the same as that recently reported by Popov
and Pappas [Phys. Rev. B 64, 184401 (2001)]. The case of a field H applied
perpendicularly to the film plane is also investigated. In both cases, the
zero-temperature equilibrium configuration is easily determined by our
theoretical approach.Comment: 4 pages, 3 figure
Critical review of Pseudocucurbitidae (Miliolina, Foraminiferea) from the Late Triassic reef environments of the Tethyan area
Abstract. The Late Triassic foraminiferal genera Amphorella, Spiriamphorella, Urnulinella, Pseudocucurbita, Paratintinnina, Costifera and Siculocosta are considered junior synonyms of the genus Cucurbita. Consequently, the number of families of the Milioliporacea (Miliolina) is significantly reduced. The valid species of the genus Cucurbita are considered to be Cucurbita infundibuliforme Jablonský, 1973, C. subsphaerica (Borza & Samuel, 1977a) comb. nov., C. longicollum Senowbari-Daryan, 1983, C. battagliensis (Senowbari-Daryan, 1983) comb. nov., C. cylindrica (Senowbari-Daryan, 1983) comb. nov. and C. floriformis (Altiner et al., 1992) comb. nov.
- …