92 research outputs found
Collapse of the hyperfine magnetic field at the Ru site in ferromagnetic rare earth intermetallics
The M\"{o}ssbauer Effect(ME) is frequently used to investigate magnetically
ordered systems. One usually assumes that the magnetic order induces a
hyperfine magnetic field, , at the ME active site. This is the
case in the ruthenates, where the temperature dependence of at
Ru sites tracks the temperature dependence of the ferromagnetic or
antiferromagnetic order. However this does not happen in the rare-earth
intermetallics, GdRu and HoRu. Specific heat, magnetization, magnetic
susceptibility, M\"{o}ssbauer effect, and neutron diffraction have been used to
study the nature of the magnetic order in these materials. Both materials are
found to order ferromagnetically at 82.3 and 15.3 K, respectively. Despite the
ferromagnetic order of the rare earth moments in both systems, there is no
evidence of a correspondingly large in the M\"{o}ssbauer
spectrum at the Ru site. Instead the measured spectra consist of a narrow peak
at all temperatures which points to the absence of magnetic order. To
understand the surprising absence of a transferred hyperfine magnetic field, we
carried out {\it ab initio} calculations which show that spin polarization is
present only on the rare-earth site. The electron spin at the Ru sites is
effectively unpolarized and, as a result, is very small at
those sites. This occurs because the 4 Ru electrons form broad conduction
bands rather than localized moments. These 4 conduction bands are polarized
in the region of the Fermi energy and mediate the interaction between the
localized rare earth moments.Comment: 34 pages -Revtex + 17 ps figure
Discovery of a binary icosahedral quasicrystal in ScZn
We report the discovery of a new binary icosahedral phase in a Sc-Zn alloy
obtained through solution-growth, producing millimeter-sized, facetted, single
grain, quasicrystals that exhibit different growth morphologies, pentagonal
dodecahedra and rhombic triacontahedra, under only marginally different growth
conditions. These two morphologies manifest different degrees of
quasicrystalline order, or phason strain. The discovery of i-ScZn
suggests that a reexamination of binary phase diagrams at compositions close to
crystalline approximant structures may reveal other, new binary
quasicrystalline phases.Comment: Incorrect spelling in author list resolve
Itinerant-Electron Magnet of the Pyrochlore Lattice: Indium-Doped YMn2Zn20
We report on a ternary intermetallic compound, "YMn2Zn20", comprising a
pyrochlore lattice made of Mn atoms. A series of In-doped single crystals
undergo no magnetic long-range order down to 0.4 K, in spite of the fact that
the Mn atom carries a local magnetic moment at high temperatures, showing
Curie-Weiss magnetism. However, In-rich crystals exhibit spin-glass transitions
at approximately 10 K due to a disorder arising from the substitution, while,
with decreasing In content, the spin-glass transition temperature is reduced to
1 K. Then, heat capacity divided by temperature approaches a large value of 280
mJ K-2 mol-1, suggesting a significantly large mass enhancement for conduction
electrons. This heavy-fermion-like behavior is not induced by the Kondo effect
as in ordinary f-electron compounds, but by an alternative mechanism related to
the geometrical frustration on the pyrochlore lattice, as in (Y,Sc)Mn2 and
LiV2O4, which may allow spin entropy to survive down to low temperatures and to
couple with conduction electrons.Comment: 5 pages, 4 figures, J. Phys. Soc. Jpn., in pres
Enhanced Reactivity of Lithium and Copper at High Pressure
High pressure can profoundly affect the electronic structure and reactivity, creating compounds between elements that do not react at ambient conditions. Lithium is known to react with gold and silver; however, no copper compounds are known to date. By compressing mixtures of the elements in diamond-anvil cells, compounds of lithium and copper have been synthesized and characterized by X-ray diffraction for the first time. Pressures as low as 1 GPa lead to the formation of a complex layered phase LiCu, displaying two-dimensional kagomé lattice layers of Cu atoms. With increasing pressure, the layered Cu–Cu bonding is replaced by linear chains of Cu atoms in the high-pressure phase LiCu. Here we show the powerful effects of even modest pressures on the reactivity of lithium, leading to structures of remarkable complexity and low-dimensional transition metal bonding
Variation of the magnetic ordering in GdTZn (T= Fe, Ru, Os, Co, Rh and Ir) and its correlation with the electronic structure of isostructural YTZn
Magnetization, resistivity and specific heat measurements were performed on
the solution-grown, single crystals of six GdTZn (T = Fe, Ru, Os,
Co, Rh and Ir) compounds, as well as their Y analogues. For the Gd compounds,
the Fe column members manifest a ferromagnetic (FM) ground state (with an
enhanced Curie temperature, , for T = Fe and Ru), whereas the
Co column members manifest an antiferromagnetic (AFM) ground state.
Thermodynamic measurements on the YTZn revealed that the enhanced
for GdFeZn and GdRuZn can be understood
within the framework of Heisenberg moments embedded in a nearly ferromagnetic
Fermi liquid. Furthermore, electronic structure calculations indicate that this
significant enhancement is due to large, close to the Stoner FM criterion,
transition metal partial density of states at Fermi level, whereas the change
of FM to AFM ordering is associated with filling of electronic states with two
additional electrons per formula unit. The degree of this sensitivity is
addressed by the studies of the pseudo-ternary compounds
Gd(FeCo)Zn and Y(FeCo)Zn which
clearly reveal the effect of 3d band filling on their magnetic properties.Comment: 32 pages, 28 figure
Compounds with Th6Mn23-type structures in alloys of the rare-earth metals with manganese and iron
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