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E P Wohlfarth

Bio: E P Wohlfarth is an academic researcher from Imperial College London. The author has contributed to research in topics: Transition metal & Electronic band structure. The author has an hindex of 1, co-authored 1 publications receiving 148 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the Curie temperature of Fe, Co and Ni as well as of their compounds with Y (including Y2Fe14B) are calculated by including the effects of spin fluctuations in the long wavelength limit via a renormalisation of Landau coefficients.
Abstract: The Curie temperature of Fe, Co and Ni as well as of their compounds with Y (including Y2Fe14B) are calculated by including the effects of spin fluctuations in the long wavelength limit via a renormalisation of Landau coefficients. The numerical values depend on the use of recent calculations of correlation effects and of the band structure. As a result, good agreement is found with the experimental values of TC of the materials covered.

154 citations


Cited by
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Journal ArticleDOI
14 Sep 2017-Nature
TL;DR: It is shown that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.
Abstract: The ability to control chemical and physical structuring at the nanometre scale is important for developing high-performance thermoelectric materials. Progress in this area has been achieved mainly by enhancing phonon scattering and consequently decreasing the thermal conductivity of the lattice through the design of either interface structures at nanometre or mesoscopic length scales or multiscale hierarchical architectures. A nanostructuring approach that enables electron transport as well as phonon transport to be manipulated could potentially lead to further enhancements in thermoelectric performance. Here we show that by embedding nanoparticles of a soft magnetic material in a thermoelectric matrix we achieve dual control of phonon- and electron-transport properties. The properties of the nanoparticles-in particular, their superparamagnetic behaviour (in which the nanoparticles can be magnetized similarly to a paramagnet under an external magnetic field)-lead to three kinds of thermoelectromagnetic effect: charge transfer from the magnetic inclusions to the matrix; multiple scattering of electrons by superparamagnetic fluctuations; and enhanced phonon scattering as a result of both the magnetic fluctuations and the nanostructures themselves. We show that together these effects can effectively manipulate electron and phonon transport at nanometre and mesoscopic length scales and thereby improve the thermoelectric performance of the resulting nanocomposites.

432 citations

Journal ArticleDOI
TL;DR: In this paper, the band structure theory of magnetism in 3d-4f compounds is reviewed, and the cornerstones of the DFT are explicitly sketched, as well as recent developments needed to cope with the treatment of localized 4f and itinerant 3d magnetisms in one and the same framework.
Abstract: The band structure theory of magnetism in 3d-4f compounds is reviewed. Among the open-shell electrons, a hierarchy of interactions is present which governs the intrinsic magnetic properties of these materials. Density functional theory (DFT) is an appropriate tool to describe and quantitatively investigate both ground state properties and model interaction parameters, which are necessary to calculate the temperature-dependent behaviour. The cornerstones of the DFT are explicitly sketched, as well as recent developments needed to cope with the treatment of localized 4f and itinerant 3d magnetism in one and the same framework. This includes the open-core scheme, self-interaction corrected DFT, relativistic DFT, and orbital polarization. On this basis, the exchange coupling among itinerant and localized states can be understood, together with the size of Curie temperature and ground state spin and orbital magnetic moments. Finally, the problem of magnetocrystalline anisotropy is addressed, concerning both the band and the 4f crystal field contribution.

158 citations

Journal ArticleDOI
TL;DR: In this paper, a comparative study of the band structure on the basis of local spin-density functional theory is presented for the ferrites Fe 3 O 4, CoFe 2 O 4, NiFe 2O 4, MnFe 2 OD 4 and ZnFe 2 OM 4.

126 citations

Book ChapterDOI
TL;DR: In this article, the magnetic properties of binary rare-earth 3d-transition-metal intermetallic compounds are discussed, and the basic concepts related to intrinsic magnetic properties related to the 3D-rich R n T m (R = rare earths; T = 3d heavy transition metals Mn, Fe, Co, Ni) intermetallics are discussed.
Abstract: Publisher Summary This chapter discusses the magnetic properties of binary rare-earth 3d-transition-metal intermetallic compounds The basic concepts related to the intrinsic magnetic properties of the 3d-rich R n T m (R = rare earths; T = 3d heavy transition metals Mn, Fe, Co, Ni) intermetallic compounds are discussed The study of rare-earth transition-metal intermetallic compounds has a number of interesting aspects Owing to the wide range of intermetallics and their different stoichiometries and variable rare-earth elements, modifications of magnetic properties of 3d transition-metal and 4f rare-earth ions can be investigated systematically These investigations illuminate the complex interactions in which the 3d and 4f electrons are involved The rare-earth metals in their ‘normal’ state where the magnetic properties of the ion cores are well defined The 4f electrons are positioned within the ion cores and hybridization with the conduction-band-electron states is negligible This situation is realized for most iron- and cobalt-based compounds with 4f elements The Ce and Yb ions, which sometimes demonstrate unusual properties connected with valence fluctuations, tend to behave quite normally in the compounds with iron or cobalt Nevertheless, there are some anomalies in the Ce compounds that can be ascribed to a mixed-valence state of the cerium ion

82 citations