Magnetic ordering in Ce 3Cu 4Sn 4 and Ce 3Cu 4Ge 4

Abstract

Specific heat, magnetic susceptibility, magnetization and neutron diffraction measurements were carried out on Ce 3Cu 4Sn 4 and Ce 3Cu 4Ge 4 compounds (structure type Gd 3Cu 4Ge 4, Immm, 2 Ce sites). The linear coefficient of specific heat is γ=330 mJ/mol Ce K 2 for the stannide and γ=225 mJ/mol Ce K 2 for the germanide, indicative for heavy fermion behaviour. The Ruderman–Kittel–Kasuya–Yosida exchange interactions in the presence of the magnetocrystalline anisotropy induce magnetic ordering, which is complex and proceeds in several steps. For both compounds below the Néel temperature T N=10.3 K incommensurate magnetic arrangements are favoured. They lock into a commensurate structure with the wave vector q 3=(0 0 0) at T 2 ( T 2=7.3 K for stannide and T′ 2=7.8 K for germanide). Due to a strong anisotropy the Ce magnetic moments are aligned along the x-axis in the T 2– T 3 interval, but at T 3= T′ 3=2.6 K a reorientation of the moments into the xy-plane occurs. The evolution of the magnetic order and the moment values differ for the two inequivalent crystallographic Ce sites. The ordered Ce magnetic moment is 2.05(2) μ B at the 2d site and 1.10(2) μ B at the 4e site for germanide. For stannide the corresponding values are 0.75(1) μ B and 1.94(2) μ B. Two different magnetic arrangements are possible for Ce 3Cu 4Sn 4 at low temperatures.