Journal of Magnetism and Magnetic Materials 210 (2000) 225}232 Neutron di!raction study of the U(Pd  Fe  )  Ge  magnetic structure A.M. Balagurov, E.V. Raspopina, V.V. Sikolenko, I.S. Lyubutin*, A.S. Stepin, A.V. Gribanov, G. Andre H , F. Boure H e, H.M. Duh Frank Laboratory of Neutron Physics, JINR, 141980 Dubna, Russia Institute of Crystallography, Russian Academy of Sciences, Leninsky pr. 59, Moscow 117333, Russia Moscow State University, Moscow 117234, Russia Laboratoire Le & on Brillouin, CEA-CNRS, CE-Saclay, 91191 Gif-sur-Yvette, France Department of Physics, National Kaohsiung Normal University, Kaohsiung, Taiwan 802, ROC Received 9 April 1999; received in revised form 22 July 1999 Abstract The neutron di!raction and magnetic susceptibility studies have shown that the magnetic structure of UPd  Ge  changes dramatically even under very low iron doping. Though the general magnetic structure of pure UPd  Ge  and of 1%Fe-doped samples is the same, the temperature intervals of existence of di!erent magnetic phases are di!erent. The values of transition temperatures, where (i) the &square' modulated longitudinal spin-density wave (LSDW) structure with the propagation vector k"(0; 0; k  "  ) 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  Ge  , the magnetic transition from the commensurate to incommensurate phase is accompanied by the drastic decrease of the propagation vector k  . In the 2%Fe-doped sample, besides the Ne H el point of ¹  "135 K, we have found two additional characteristic temper- atures 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(¹(¹  , the magnetic structure is LSDW with sinusoidal modulation. Over almost the total region 65 K(¹(¹  , the LSDW magnetic structure is incommensurate. Only at about 93 K, the propagation vector passes the commensurate value of   , whereas k  '  at 65(¹(93 K and k  (  at 93 K(¹(¹  . We have found that the magnetic susceptibility and the uranium magnetic moment are sensitive to the k  '  Nk  (  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 Ne H el point. Below ¹  , the uranium magnetic moments are always parallel to the tetragonal c-axis.  2000 Elsevier Science B.V. All rights reserved. PACS: 75.25.#z; 75.30.Fv; 75.30.Kz; 75.50.Ee Keywords: Neutron di!raction; Modulated spin-density wave structures; Magnetic transitions * Corresponding author. Tel./fax: #7-095-330-8329. E-mail address: lyubutin@magnet.crystal.msk.su (I.S. Lyubutin) 0304-8853/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 9 ) 0 0 6 1 0 - 1