Structure and magnetic properties of TbMn6Sn6-x Tix (x=0-0.9) compounds

The effects of Ti substitution for Sn on the structure and magnetic properties of TbMn₆Sn_6-xTi_x (x=0-0.9) compounds have been investigated by means of X-ray diffraction (XRD), magnetization measurements and ¹¹⁹Sn Mossbauer spectroscopy. The substitution of Ti for Sn results in an increase in the lattice constants and the unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ti content from 423 K for x=0 to 376 K for x=0.9. At room temperature, the easy magnetization direction changes from the c-axis for x<0.3, to the cone for 0.3<x<0.9 and then to the ab-plane for x=0.9. This variation implies that the substitution of Ti for Sn leads to a decrease in the c-axis anisotropy of the Tb sublattice. An increase in the nonmagnetic Ti concentration results in a monotonic decrease of the spontaneous magnetization M_s at both 5 K and room temperature. Since there are three nonequivalent Sn sites, 2c(0.33, 0.67, 0), 2d(0,33, 0.67, 0.5) and 2e(0, 0, 0.34) in the TbMn₆Sn_6-xTi_x compounds, the ¹¹⁹ Sn Mossbauer spectra of the TbMn₆Sn₆ and TbMn₆Sn_5.4Ti_0.6 compounds can be fitted by three sextets. The hyperfine fields, HFs, decrease in the order of HF(2d)>HF(2e)>HP(2c), which is in agreement with the magnetic structure