Crystal and magnetic structure of Eu4Ga8Ge16
Abstract
The antiferromagnetic ordering and crystal structure of the clathrate compound Eu4Ga8Ge16 was investigated using multitemperature neutron and synchrotron x-ray powder diffraction. High-resolution low-Q neutron data were measured at long wavelength (λ=4.2 Å) between 1.5 and 15 K for an accurate description of the magnetic structure, whereas high-Q diffraction patterns were collected using neutrons of wavelength 1.9 Å at the same temperatures to determine the nuclear structure precisely. The structure orders antiferromagnetically at about 8 K with ferromagnetic chains parallel to the a axis. The intrachain Eu-Eu distance, 4.1216(1) Å at 1.5 K, is significantly shorter than the distance observed in the ferromagnetic clathrates β-Eu8Ga16Ge30 (5.23 Å) and α-Eu8Ga16Ge30 (5.56 Å). Antiferromagnetic coupling to the nearest and next-nearest chains at distances of 5.99 and 6.98 Å, respectively, leads to an overall antiferromagnetic structure. A fit to a power law of the temperature dependence of the ordered Eu2+ magnetic moment results in a moment of 7.01(7)μB at 0 K in agreement with the 7μB for the free ion value of Eu2+. The temperature dependence of the crystal structure was investigated from 11 K to room temperature using synchrotron x-ray powder diffraction. Analysis of the atomic displacement parameters with Einstein and Debye models gives ΘE=82(3) K for the guest atom and ΘD=266(4) K for the framework atoms. Based on ΘD the lattice contribution to thermal conductivity is estimated to be 0.0125 W/cm K.
- Publication:
-
Physical Review B
- Pub Date:
- November 2003
- DOI:
- 10.1103/PhysRevB.68.174428
- Bibcode:
- 2003PhRvB..68q4428C
- Keywords:
-
- 75.50.Ee;
- 61.10.Nz;
- 61.12.Ld;
- 72.15.Eb;
- Antiferromagnetics;
- X-ray diffraction;
- Neutron diffraction;
- Electrical and thermal conduction in crystalline metals and alloys