Neutron diffraction study of the U(Pd 1− xFe x) 2Ge 2 magnetic structure

Abstract

The neutron diffraction and magnetic susceptibility studies have shown that the magnetic structure of UPd 2Ge 2 changes dramatically even under very low iron doping. Though the general magnetic structure of pure UPd 2Ge 2 and of 1%Fe-doped samples is the same, the temperature intervals of existence of different magnetic phases are different. The values of transition temperatures, where (i) the `square’ modulated longitudinal spin-density wave (LSDW) structure with the propagation vector k =(0; 0; k z= 3 4 ) starts to transform into the sinusoidal modulated LSDW structure and (ii) the commensurate phase transforms into incommensurate one, shift under the 1%Fe doping to the higher temperatures (from 50 to 65 K and from 80 to 90 K, respectively). In the pure and 1%Fe-doped UPd 2Ge 2, the magnetic transition from the commensurate to incommensurate phase is accompanied by the drastic decrease of the propagation vector k z . In the 2%Fe-doped sample, besides the Néel point of T N=135 K, we have found two additional characteristic temperatures of 65 and 93 K. Below 65 K, the material has a simple antiferromagnetic (AF) structure with the propagation vector k=(0; 0; 1) and, at 65 K< T< T N, the magnetic structure is LSDW with sinusoidal modulation. Over almost the total region 65 K< T< T N, the LSDW magnetic structure is incommensurate. Only at about 93 K, the propagation vector passes the commensurate value of 3 4 , whereas k z> 3 4 at 65< T<93 K and k z< 3 4 at 93 K< T< T N. We have found that the magnetic susceptibility and the uranium magnetic moment are sensitive to the k z> 3 4 ⇒k z< 3 4 transition. With increasing iron concentration to x⩾0.15, the simple AF structure with k=(0; 0; 1) develops over all temperature region up to the Néel point. Below T N, the uranium magnetic moments are always parallel to the tetragonal c-axis.