Magnetic and Crystal Structures of ErC2 at 297–2°K

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Abstract
Neutron‐powder diffraction measurements show that the tetragonal body‐centered ErC2 becomes antiferromagnetic below 19 ± 2° K . The moment alignment is governed by several narrowly dispersed, incommensurate transverse magnetization waves. The major modulation waves propagate along the a axis and are polarized in the b axis direction. The magnetization wavelengths are 5.78, 5.4, 6.7, and 7.1 Å, and the amplitudes are respectively 6.55, 2.2, 2.1, and 1.6 μ B at 4.2°K. The ferromagnetic alignment in the plane perpendicular to a is slightly altered by several long‐periodicity modulations propagating along the b and c axes. A commensurate, antiferromagnetic wave also participates in the moment alignment below 10 ± 3° K . The commensurate wave is represented by setting the wavelength equal to the a spacing in the incommensurate wave mode. The commensurate moment is 2.5 μ B at 4.2°K. The root‐mean‐square value of all the moment amplitudes is 7.8 μ B at 4.2°K and increases to 7.9 μ B at 2°K. These features are likely caused by a strong perturbation between the RKKY coupling and the crystal‐field effect. The proposed structure is by no means unique, although an exhaustive search for other probable models was fruitless. The crystal structure is characterized by the C – C bonding distance of 1.288 ± 0.006 Å and the Er – C distances of 2.403 ± 0.003 and 2.640 ± 0.001 Å . These distances are indicative of a large 5d‐π g 2p contribution in the conduction‐band wavefunction.

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