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Structure factors for a small holmium diiron HoFe2 Laves crystal were measured with focused λ = 0.75 Å synchrotron X-radiation using a fast avalanche photodiode (APD) counter. The deformation electron density (Δρ) maps are remarkable for significant excess electron density midway between the Ho atoms, which is not dissimilar to the peaks attributed to classic `covalent bonding' in C and Si crystals. These residual electrons accumulate at the centres of the kagomé net hexagons and form, with the Fe atoms, a triangular lattice which is characterized by more stable magnetic order than the kagomé net. Similar peaks occur along the Ho–Fe and Fe–Fe contacts. These results confirm the hypothesis that 5d electrons of the rare-earth atoms are important in the spin-coupling mechanism for HoFe2-type compounds. The 5d electrons are far less localized than the 4f electrons, and considerable 5d–5d and 5d–3d orbital overlap occurs between neighbouring atoms. Aspherical electron density near the Ho nuclei can be associated with the Ho 4f subshell electrons. Strong depletions of the Δρ near the atoms along the Ho–Ho, Ho–Fe and Fe–Fe vectors are indications of exchange repulsion. The effect of anharmonicity on the Δρ is insignificant.

Supporting information

cif

Crystallographic Information File (CIF)
Contains datablocks lsx, default

hkl

Structure factor file (CIF format)
Contains datablock lsx

Computing details top

Data collection: BL14A_Photon_Factory; data reduction: xtal_DIFDAT_ADDREF_SORTRF_ABSORB; program(s) used to solve structure: Xtal; program(s) used to refine structure: xtal_CRYLSQ; molecular graphics: Xtal; software used to prepare material for publication: xtal_CIFIO.

(lsx) top
Crystal data top
Fe2HoDx = 9.411 Mg m3
Mr = 276.62Xray_vertical_wiggler radiation, λ = 0.75 Å
Cubic, Fd3mCell parameters from 6 reflections
Hall symbol: -F 4vw 2vw 3θ = 24.2–24.2°
a = 7.3091 (6) ŵ = 60.63 mm1
V = 390.47 (10) Å3T = 293 K
Z = 8, black
F(000) = 9520.02 × 0.02 × 0.0032 mm
Data collection top
BL14A 4 circle
diffractometer
116 reflections with I > 2σ(I)
Radiation source: BL14A_Photon_FactoryRint = 0.067
Si(111)_double monochromatorθmax = 55.2°, θmin = 5.1°
ω–2θ scansh = 1616
Absorption correction: analytical
xtal_ABSORB
k = 1616
Tmin = 0.433, Tmax = 0.823l = 1616
3381 measured reflections6 standard reflections every 94 reflections
116 independent reflections intensity decay: 3.7%
Refinement top
Refinement on F0 constraints
Least-squares matrix: fullw = 1/σ2(F)
R[F2 > 2σ(F2)] = 0.010(Δ/σ)max < 0.001
wR(F2) = 0.011Δρmax = 1.58 e Å3
S = 1.40Δρmin = 0.70 e Å3
116 reflectionsExtinction correction: Maslen & Spadaccini (1993)
4 parametersExtinction coefficient: 0.00000
0 restraints
Special details top

Refinement. Sfls F σ weight full matrix

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ho0.125000.125000.125000.006726 (18)
Fe0.500000.500000.500000.00667 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ho0.006726 (18)0.006726 (18)0.006726 (18)0.000000.000000.00000
Fe0.00667 (4)0.00667 (4)0.00667 (4)0.00012 (5)0.00012 (5)0.00012 (5)
Bond lengths (Å) top
Ho—Hoi3.1649 (2)Fe—Feii2.5842 (2)
Ho—Feii3.0302 (2)
Symmetry codes: (i) y, x+1/4, z+1/4; (ii) x+3/4, y, z+3/4.
 
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