75 research outputs found
Temperature dependent magnetic anisotropy in metallic magnets from an ab-initio electronic structure theory: L1_0-ordered FePt
On the basis of a first-principles, relativistic electronic structure theory
of finite temperature metallic magnetism, we investigate the variation of
magnetic anisotropy, K, with magnetisation, M, in metallic ferromagnets. We
apply the theory to the high magnetic anisotropy material, L1_0-ordered FePt,
and find its uniaxial K consistent with a magnetic easy axis perpendicular to
the Fe/Pt layering for all M and to be proportional to M^2 for a broad range of
values of M. For small M, near the Curie temperature, the calculations pick out
the easy axis for the onset of magnetic order. Our results are in good
agreement with recent experimental measurements on this important magnetic
material.Comment: 4 pages, 2 figure
Electronic structure and x-ray magnetic dichroism in random substitutional alloys of f-electron elements
The Koringa-Kohn-Rostoker —coherent-potential-approximation method combines multiple-scattering theory and the coherent-potential approximation to calculate the electronic structure of random substitutional alloys of transition metals. In this paper we describe the generalization of this theory to describe f-electron alloys. The theory is illustrated with a calculation of the electronic structure and magnetic dichroism curves for a random substitutional alloy containing rare-earth or actinide elements from first principles
Coarse grained Density Functional theory of order-disorder phase transitions in metallic alloys
The technological performances of metallic compounds are largely influenced
by atomic ordering. Although there is a general consensus that successful
theories of metallic systems should account for the quantum nature of the
electronic glue, existing non-perturbative high-temperature treatments are
based on effective classical atomic Hamiltonians. We propose a solution for the
above paradox and offer a fully quantum mechanical, though approximate, theory
that on equal footing deals with both electrons and ions. By taking advantage
of a coarse grained formulation of the density functional theory [Bruno et al.,
Phys. Rev. B 77, 155108 (2008)] we develop a MonteCarlo technique, based on an
ab initio Hamiltonian, that allows for the efficient evaluation of finite
temperature statistical averages. Calculations of the relevant thermodynamic
quantities and of the electronic structures for CuZn and NiV support that
our theory provides an appropriate description of order-disorder phase
transitions.Comment: 4 pages, 4 figure
Spin fluctuations in nearly magnetic metals from ab-initio dynamical spin susceptibility calculations:application to Pd and Cr95V5
We describe our theoretical formalism and computational scheme for making
ab-initio calculations of the dynamic paramagnetic spin susceptibilities of
metals and alloys at finite temperatures. Its basis is Time-Dependent Density
Functional Theory within an electronic multiple scattering, imaginary time
Green function formalism. Results receive a natural interpretation in terms of
overdamped oscillator systems making them suitable for incorporation into spin
fluctuation theories. For illustration we apply our method to the nearly
ferromagnetic metal Pd and the nearly antiferromagnetic chromium alloy Cr95V5.
We compare and contrast the spin dynamics of these two metals and in each case
identify those fluctuations with relaxation times much longer than typical
electronic `hopping times'Comment: 21 pages, 9 figures. To appear in Physical Review B (July 2000
Alle origini dei comuni rurali, (a prop. di C. WICKHAM, Comunità e clientele nella Toscana del XII secolo. Le origini del comune rurale nella Piana di Lucca, Roma, Viella, 1995)
Tracce di antroponimia dai documenti dell'Abbazia di San Salvatore a Isola, Siena (953-1139),
Corpi e uomini tra scienza e storia: studi di osteo-archeologia umana per l'Italia medievale
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