We present first results of
ab initio computations within the density functional theory in order to study the differences in chemical bonding and the experimentally observed different magnetic ...behaviour of the orthorhombic, TiNiSi related ternary germanides CeRhGe (antiferromagnet) and CeIrGe (intermediate valence compound). The calculations reveal strong contributions of the cerium 4f states at the Fermi level. Ingoing from CeRhGe to CeIrGe stronger Ce–Ir
versus Ce–Rh interactions are found.
Display omitted
The stannides ScAuSn, YAuSn, and LuAuSn were synthesized as single phase materials from the elements via arc-melting. All samples were characterized by X-ray diffraction on powders and single ...crystals: MgAgAs type,
F
4
¯
3
m
,
a
=
641.94
(
12
)
pm
,
w
R
2
=
0.035
, 85
F
2
values, 5 variables for ScAuSn,
a
=
656.52
(
8
)
pm
,
w
R
2
=
0.029
, 89
F
2
values, 5 variables for LuAuSn, and NdPtSb type,
P
6
3
m
c
,
a
=
463.55
(
16
)
,
c
=
737.26
(
15
)
pm
,
w
R
2
=
0.057
, 233
F
2
values, 11 variables for YAuSn. The gold and tin atoms in ScAuSn and LuAuSn build up three-dimensional AuSn networks of corner-sharing AuSn
4/4 tetrahedra (278 and 284 pm Au
Sn in ScAuSn and LuAuSn, respectively) similar to the blende type structure. The scandium atoms fill octahedral voids formed by the tin substructure. In contrast, the AuSn network of YAuSn is two-dimensional. The gold and tin atoms build up layers of puckered Au
3Sn
3 hexagons with intralayer Au
Sn distances of 277 pm, while the interlayer Au
Sn distances of 297 pm are much longer. In every other layer the Au
3Sn
3 hexagons are rotated by 60°. The layers are separated by the yttrium atoms. Spectroscopic measurements indicate significant differences in the chemical bonding properties: As revealed by both
119Sn Mössbauer spectroscopy and
119Sn solid-state NMR data, the local electronic environment at the tin site is more anisotropic in YAuSn as compared to the other materials, which feature tin on a site with cubic point symmetry. In ScAuSn, the cubic site symmetry of the scandium position is reflected by a single sharp line in the
45Sc solid-state NMR spectrum.
Magnetic ordering in CeCoGe3 DAS, A; KREMER, R. K; PÖTTGEN, R ...
Physica. B, Condensed matter,
05/2006, Letnik:
378-80
Conference Proceeding, Journal Article
Recenzirano
CeCoGe3 crystallizes with the BaNiSn3-type structure. The temperature variation of the magnetization exhibits an increase below 20K with a further broad peak at . Powder neutron diffraction ...experiments as a function of temperature show evidence of long-range antiferromagnetic ordering. On application of a magnetic field, the ferromagnetic moment appears to recover.
Complex charge ordering in CeRuSn Feyerherm, R.; Dudzik, E.; Valencia, S. ...
Physical review. B, Condensed matter and materials physics,
02/2012, Letnik:
85, Številka:
8
Journal Article
Odprti dostop
At ambient temperatures, CeRuSn exhibits an extraordinary structure with a coexistence of two types of Ce ions in a metallic environment, namely trivalent Cesup 3+ and intermediate valent Cesup (4- ...delta )+ . Charge ordering produces a doubling of the unit cell along the axis with respect to the basic monoclinic CeCoAl type structure. Below room temperature, a phase transition with very broad hysteresis has been observed in various bulk properties like electrical resistivity, magnetic susceptibility, and specific heat. The present x-ray-diffraction results show that at low temperatures the doubling of the CeCoAl type structure is replaced by an ill-defined modulated ground state. In this state, at least three different modulation periods compete, with the dominant mode close to a tripling of the basic cell. The transition is accompanied by a significant contraction of the axis. XANES data suggest that the average Ce valence remains constant; thus the observed axis contraction is not due to any valence transition. Thus CeRuSn exhibits both thermally and x-ray induced reversible transformations of the Cesup 3+/Cesup (4- delta )+ charge-ordering pattern.
We report on the spin densities in CeRuSn determined at elevated and at low temperatures using polarized neutron diffraction. At 285 K, where the CeRuSn crystal structure contains two different ...crystallographic Ce sites, we observe that a Ce site with larger nearest-neighbor distances is clearly more susceptible to the applied magnetic field, whereas the other is hardly polarizable. This finding clearly documents that different local environment of the two Ce sites causes the Ce ions to split into magnetic Ce super(3+) and magnetic Ce super((4- delta )+) valence states. With lowering the temperature, the crystal structure transforms to a structure incommensurately modulated along the c axis. This leads to new inequivalent crystallographic Ce sites resulting in a redistribution of spin densities. Our analysis using the simplest structural approximant shows that in this metallic system Ce ions coexist in different valence states. Localized 4f states that fulfill the third Hund's rule are found to be close to the ideal Ce super(3+) state (at sites with the largest Ce-Ru interatomic distances), whereas Ce super((4- delta )+) valence states are found to be itinerant and situated at Ce sites with much shorter Ce-Ru distances. The similarity to the famous gamma - alpha transition in elemental cerium is discussed.
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