113 research outputs found
Magnetic structures of Mn3-xFexSn2: an experimental and theoretical study
We investigate the magnetic structure of Mn3-xFexSn2 using neutron powder
diffraction experiments and electronic structure calculations. These alloys
crystallize in the orthorhombic Ni3Sn2 type of structure (Pnma) and comprise
two inequivalent sites for the transition metal atoms (4c and 8d) and two Sn
sites (4c and 4c). The neutron data show that the substituting Fe atoms
predominantly occupy the 4c transition metal site and carry a lower magnetic
moment than Mn atoms. Four kinds of magnetic structures are encountered as a
function of temperature and composition: two simple ferromagnetic structures
(with the magnetic moments pointing along the b or c axis) and two canted
ferromagnetic arrangements (with the ferromagnetic component pointing along the
b or c axis). Electronic structure calculations results agree well with the
low-temperature experimental magnetic moments and canting angles throughout the
series. Comparisons between collinear and non-collinear computations show that
the canted state is stabilized by a band mechanism through the opening of a
hybridization gap. Synchrotron powder diffraction experiments on Mn3Sn2 reveal
a weak monoclinic distortion at low temperature (90.08 deg at 175 K). This
lowering of symmetry could explain the stabilization of the c-axis canted
ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a
circumstance that would otherwise require unusually large high-order terms in
the spin Hamiltonian.Comment: 11 pages, 13 figure
Electronic structure and magnetic properties of RMnX (R= Mg, Ca, Sr, Ba, Y; X= Si, Ge) studied by KKR method
Electronic structure calculations, using the charge and spin self-consistent
Korringa- Kohn-Rostoker (KKR) method, have been performed for several Mn
compounds ( = Mg, Ca, Sr, Ba, Y; = Si, Ge) of the CeFeSi-type structure.
The origin of their magnetic properties has been investigated emphasizing the
role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-
interatomic distances on the Mn magnetic moment value is delineated from our
computations, supporting many neutron diffraction data. We show that the marked
change of with the Mn-Mn and Mn- distances resulted from a
redistribution between spin-up and spin-down -Mn DOS rather than from
different fillings of the Mn 3-shell. Bearing in mind that the neutron
diffraction data reported for the Mn compounds are rather scattered, the
KKR computations of are in fair agreement with the experimental
values. Comparing density of states near obtained in different magnetic
orderings, one can notice that the entitled Mn systems seem to 'adapt'
their magnetic structures to minimize the DOS in the vicinity of the Fermi
level. Noteworthy, the SrMnGe antiferromagnet exhibits a pseudo-gap behaviour
at , suggesting anomalous electron transport properties. In addition,
the F-AF transition occurring in the disordered LaYMnSi alloy for
the range is well supported by the DOS features of
LaYMnSi. In contrast to the investigated Mn compounds,
YFeSi was found to be non-magnetic, which is in excellent agreement with the
experimental data.Comment: 10 pages + 14 figures, to appear in Eur. Phys. Jour.
Magnetocaloric properties of Fe_{2-x}T_xP (T = Ru and Rh) from electronic structure calculations and magnetisation measurements
An analysis of the magnetocaloric properties of the pure and substituted Fe2P
compounds is made based on KKR-CPA electronic structure calculations and
magnetisation M(H,T) measurements. The computed electronic densities of states
and magnetic moments are used to calculate both the values of the electronic
and magnetic entropies, which fairly agree with the experimental findings. To
enlighten the magnetic properties above Curie temperature, the paramagnetic
state behaviours are simulated using the disordered local moments (DLM)
concept. The KKR-CPA computations show, that in Fe2P, the Fe magnetic moment of
the (3f) site disappears in the DLM state, while the moment of the (3g) site is
only little lowered, comparison made with the low temperature ferromagnetic
state.Comment: 17 pages, 8 figures, Submitted to J. Phys.
Deux nouveaux ternaires à structures apparentées: TiSnSb de type CuMg2 et NbSnSb de type CuAl2
B2 long-range order in mechanically alloyed Fe 53.3-0.6x Co 46.7-0.4x Sn x (2 ≤ x ≤ 26) annealed at moderate temperatures
International audienceRecent interest in Fe-Co-Sn alloys stems from Heusler alloys. A Co2FeSn Heusler alloy is found to be unstable relative to other phases from ab initio calculations. However, it may be synthesized by non-equilibrium techniques. The present work focuses similarly on metastable ordered phases in ternary Fe-Co-Sn alloys. First, disordered phases of Sn in near-equiatomic Fe-Co are prepared by high-energy ball-milling. As-milled powders are then annealed to possibly produce long-range ordered phases. As-milled powders, of overall composition Fe53.3-0.6xCo46.7-0.4xSnx (2 ≤ x ≤ 34), consist of a single supersaturated bcc phase for x<~15 at.%. For larger values of x, they are primarily composed of a bcc phase, whose tin content still increases up to ~26 at.%, and of extra phases, which include hexagonal (Fe,Co)3Sn2. Neutron diffraction patterns and 119Sn Mössbauer spectra prove that bcc phases of as-milled alloys order to CsCl (B2) type structures for x ≤ 26 when annealed at 673K. In addition, 119Sn Mössbauer spectra reveal that a Sn content of ~15 at.% marks the separation between domains with different short-range orders. From previous and present results, metastable B2 ordering of Sn-rich Co-Fe-Sn alloys is concluded to occur over a significant concentration range
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