Magnetic structure of the Zr 6CoAs 2-type Er 6TX 2 compounds (T = Mn, Fe, Co and X = Sb, Bi)

Abstract

Investigations were made by neutron diffraction on the Zr 6CoAs 2-type (space group P6b2m, No. 189) Er 6FeSb 2, Er 6MnSb 2, Er 6CoBi 2, Er 6FeBi 2, Er 6MnBi 2 and Zr 6MnBi 2 compounds. The Er 6FeSb 2, Er 6MnSb 2, Er 6CoBi 2 and Er 6MnBi 2 compounds show a ferromagnetic type of ordering below 21(5), 110(5), 30(2) and 100(5) K, respectively. Below the ferromagnetic transition the magnetic structure of these compounds consist of Er ferromagnetic (1 0 0) layers. Below 33(25) K, the Er 6MnBi 2 compound has an incommensurate magnetic structure with constant propagation vectors [0.596(2), 0, 0]. The propagation vector coincides with the a-axis of the unit cell. The magnetic moments of the Er atoms make an angle with the c-axis ( μ Er = 7.5(2) μ B, β Er = 6.7(4)° at 2 K). The Er 6FeBi 2 compound displays a ferromagnetic transition below 15(5) K. The magnetic structure of the Er 6FeBi 2 compound is not clear. In the Er 6TX 2 compounds, no local moment was detected on the transition metal site. Furthermore, no magnetic transition was detected in the Zr 6CoAs 2-type Zr 6MnBi 2 compound. Both, the type of transition metal and the distortion of the unit cell strongly influence the ferromagnetic type of ordering temperature and the magnetic structure in these compounds.