Investigation of spin-reorientation phase transitions in single-crystal DyFe11Ti

Abstract

In this paper we study the phenomenon of spin reorientation in the compound DyFe11Ti, which has a tetragonal crystal structure of ThMn12 type. We experimentally measured curves for the mechanical torque that acts on singlecrystal samples placed in a magnetic field. Literature data on the spin-reorientation transition temperatures in this compound and on the character of the spin reorientation are quite contradictory. Thus, for example, Hsu et al. observed that a second-order spin-reorientation transition takes place in DyFe11Ti at T15 200 K and a first-order spinreorientation transition at T2558 K, whereas Kudrevatykh et al. 1 reported that the second transition occurs at T25120 K. Only one spin-reorientation transition was observed in Ref. 3. Analysis of the other papers also results in contradictory information, since the measurements ~primarily studies of the temperature dependence of the magnetic susceptibility and magnetization! were most often made on oriented powder samples by methods that do not allow an unambiguous answer to the question about the nature of the spinreorientation transition. This prompted us to investigate the spin-reorientation transition in DyFe11Ti single crystals. The technology for obtaining single crystals and the method for making measurements were described previously in Refs. 7,8. For the magnetic measurements we took samples whose crystallographic axes in single-crystal blocks were misoriented by no more than 3°. Samples cut along the crystallographic planes ~010! and ~110! had a weight of around 30 mg; they had the shape of disks with diameter ;4 mm and thickness ; 0.5 mm. Curves of the mechanical torque L(u), where u is the angle between the crystallographic direction @001# and the field H, were plotted for a DyFe11Ti single crystal on a torque magnetometer in the temperature range 78–300 K for magnetic fields up to 13 kOe. Although a magnetic field H5 13 kOe is insufficient for saturation far from the easy magnetization axis, near this axis the magnetization curves and mechanical torques both saturated in this field. The use of stronger magnetic fields leads to such undesirable effects as disruption of the collinearity of the magnetic moments of the dysprosium and iron sublattices, which hinders the analysis of the experimental data. Figure 1 shows experimental curves for L(u) measured in the ~010! plane at various temperatures in a field H5 13 kOe. At T5 300 K the crystallographic directions @001# (L 50 and ]L/]u, 0! and @100# (L50 and ]L/]u. 0! are easy-magnetization and difficult-magnetization axes respec-