13 research outputs found
Tuning magnetocrystalline anisotropy of FeSn by alloying
The electronic structure, magnetic properties and phase formation of
hexagonal ferromagnetic FeSn-based alloys have been studied from first
principles and by experiment. The pristine FeSn compound is known to
fulfill all the requirements for a good permanent magnet, except for the
magnetocrystalline anisotropy energy (MAE). The latter is large, but planar,
i.e. the easy magnetization axis is not along the hexagonal c direction,
whereas a good permanent magnet requires the MAE to be uniaxial. Here we
consider FeSnM, where M= Si, P, Ga, Ge, As, Se, In, Sb,
Te and Bi, and show how different dopants on the Sn sublattice affect the MAE
and can alter it from planar to uniaxial. The stability of the doped FeSn
phases is elucidated theoretically via the calculations of their formation
enthalpies. A micromagnetic model is developed in order to estimate the energy
density product (BH)max and coercive field H of a potential
magnet made of FeSnSb, the most promising candidate
from theoretical studies. The phase stability and magnetic properties of the
FeSn compound doped with Sb and Mn has been checked experimentally on the
samples synthesised using the reactive crucible melting technique as well as by
solid state reaction. The FeSn-Sb compound is found to be stable when
alloyed with Mn. It is shown that even small structural changes, such as a
change of the c/a ratio or volume, that can be induced by, e.g., alloying with
Mn, can influence anisotropy and reverse it from planar to uniaxial and back
Size-induced superantiferromagnetism with reentrant spin-glass behavior in metallic nanoparticles of TbCu2
An unusual 4f -superantiferromagnetic state characterized by simultaneous antiferromagnetic and spin-glass behaviors induced by particle-size reduction is revealed in metallic nanoparticles (≈ 9 nm) of TbCu 2 . The Néel temperature is 46 K and the glassy freezing is below ≈ 9 K and governed by a critical slowing down process. Neutron diffraction at 1.8 K establishes the superantiferromagnetism. The latter is settled by the nanoparticle moments and the freezing mechanism is provided by the surface spins
Database of novel magnetic materials for high-performance permanent magnet development
This paper describes the open Novamag database that has been developed for the design of novel Rare-Earth free/lean permanent magnets. Its main features as software technologies, friendly graphical user interface, advanced search mode, plotting tool and available data are explained in detail. Following the philosophy and standards of Materials Genome Initiative, it contains significant results of novel magnetic phases with high magnetocrystalline anisotropy obtained by three computational high-throughput screening approaches based on a crystal structure prediction method using an Adaptive Genetic Algorithm, tetragonally distortion of cubic phases and tuning known phases by doping. Additionally, it also includes theoretical and experimental data about fundamental magnetic material properties such as magnetic moments, magnetocrystalline anisotropy energy, exchange parameters, Curie temperature, domain wall width, exchange stiffness, coercivity and maximum energy product, that can be used in the study and design of new promising high-performance Rare-Earth free/lean permanent magnets. The results therein contained might provide some insights into the ongoing debate about the theoretical performance limits beyond Rare-Earth based magnets. Finally, some general strategies are discussed to design possible experimental routes for exploring most promising theoretical novel materials found in the database.European Horizon 2020 Framework Programme for Research and Innovation (2014-2020) under Grant Agreement No. 686056, NOVAMAG. European Regional Development Fund in the IT4Innovations national supercomputing center – path to exascale project, project number CZ 02.1.01/0.0/0.0/16–013/0001791 within the Operational Programme Research, Development and Educatio
Unternehmenskultur und marktorientierte Unternehmensfuehrung: Bestandsaufnahme u. Wirkungsanalyse
Available from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 145990 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Surfactant-assisted production of TbCu2 nanoparticles
The production of surfactant-assisted metallic nanoparticles of TbCu2 has been achieved by the combination of high-energy ball milling in tungsten carbide containers and the use of oleic acid (C18H34O2) and heptane (C7H16). The alloys were first produced in bulk pellets by arc melting and subsequently milled for only 2 and 5 h in oleic acid (15 and 30% mass weight). The powders consist of an ensemble of nanoparticles with a TbCu2 lattice cell volume of ≈215 Å3, an average particle diameter between 9 and 12 nm and inhomogeneous lattice strain of 0.2–0.4%, as deduced from X-ray diffraction data. The nanometric sizes of the crystals with defined lattice planes are close to those obtained by transmission electron microscopy. Raman spectroscopy shows the existence of inelastic peaks between 1000 and 1650 cm−1, a characteristic of C18H34O2. The magnetisation shows a peak at the antiferromagnetic-paramagnetic transition with Néel temperatures around 48 K (below that of bulk alloy) and a distinctive metamagnetic transition at 5 K up to 40 K. The Curie-Weiss behaviour above the transition reveals effective Bohr magneton numbers (≈9.1–9.9 μB) which are close to what is expected for the free Tb3+ ion using Hund’s rules. The metamagnetic transition is slightly augmented with respect to the bulk value, reaching H = 24.5 kOe by the combined effect of the size reduction and the lattice strain increase and the increase of magnetic disorder. At low temperatures, there is irreversibility as a result of the existing magnetic disorder. The moment relaxation follows an Arrhenius model with uncompensated Tb moments, with activation energies between 295 and 326 K and pre-exponential factors between 10−11 and 10−13 s. The results are interpreted as a consequence of the existence of a diamagnetic surfactant which drastically decreases the magnetic coupling between interparticle moments
Myopic decision rules and intertemporal equilibria
SIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 148137 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman