Suppression of spin density wave character of (Sm/Gd)FeAsO by substitution of Ru at Fe site Anand Pal a , Arpita Vajpayee a, * , V.P.S. Awana a , M. Husain b , H. Kishan a a National Physical Laboratory, New Delhi 110012, India b Department of Physics, Jamia Millia Islamia, New Delhi 110 025, India article info Article history: Accepted 2 November 2009 Available online 5 November 2009 Keywords: Fe-based oxypnictides Spin density wave Ferromagnetism abstract We report synthesis, structural details and transport measurements on SmFe 0.5 Ru 0.5 AsO and GdFe 0.5 R- u 0.5 AsO. The samples are synthesized at normal pressure with vacuum encapsulation technique. The par- ent REFeAsO (RE = Sm and Gd) crystallizes in tetragonal P4/nmm space group having their lattice parameters as a = 3.9375(6) Å, c = 8.5021(4) Å for Sm and a = 3.9152(4) Å, c = 8.4546(1) Å for Gd. With 50% Ru substitution at Fe site i.e. for SmFe 0.5 Ru 0.5 AsO and GdFe 0.5 Ru 0.5 AsO the lattice parameter a is increased and c is decreased to as a = 4.0113(55) Å, c = 8.3129(17) Å for Sm and a = 3.9795(64) Å, c = 8.2787 (20) Å for Gd samples. Resistivity measurements on pristine samples though exhibited clearly the step like metallic transition at around 150 K, the Fe site 50% Ru substituted samples show all through a metallic behavior without the characteristic spin density wave (SDW) step. The samples with lower content of Ru at Fe site i.e. 10% and 30% are also studied. Though 10% Ru doped samples exhibited weak superconductivity like transition below 15 K, the 30% doped samples are metallic. It seems that the Fe 2+ site Ru 4+/5+ substitution provides electron carriers for conduction process. For achieving bulk supercon- ductivity in Fe-site Ru substituted REFeAsO (1111) systems the efforts are still underway. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The discovery of iron-based layered superconductor LaFe- AsO 1Àx F x had a great impact to the researchers in condensed-mat- ter physics [1]. Among the superconductors with several different structures raised T c up to 56 K in doped REFeAsO (RE = La, Pr, Sm, Nd, Gd) compound [1–10]. Besides the Cu-based high T c supercon- ductor, the REFeAsO is the only class of superconductor till date, having their superconducting transition temperature (T c ) beyond the Strong BCS limit i.e. about 40 K. The iron-based superconductor provides an opportunity to the researchers to explore the mecha- nism of High temperature superconductors. Unlike the Cu-based superconductors the synthesis route of the REFeAsO superconduc- tor is quite complicated. The REFeAsO compounds mainly synthesized by high-temperature high-pressure (HPHT) process with pressure as high as 4–6 GPa at 1250 °C. Some reports are available for the normal pressure synthesis is to encapsulate the sample in evacuated/Ar filled quartz tube and annealing up to 1150 °C. In the current communication, we report synthesis of the ReFe 1Àx Ru x AsO (RE = Sm and Gd, x = 0.5) in an evacuated (10 À5 Torr) quartz tube [5–8]. The resultant compounds are found to be nearly single phase but not superconducting due to lack of carriers. Here we describe the result of substitution of Ru on Fe site in REFeAsO 1111-type materials, which fully suppresses the spin density wave behavior in a metallic state that does not exhibit superconductivity above 22 K. The polycrystalline samples of (Sm/Gd)Fe 1Àx Ru x AsO were syn- thesized by using a two-step solid state reaction method. Firstly, the Sm (Alfa Aesar, 99.9%) and As (Alfa Aesar, 99%) chips were sealed in evacuated quartz tube and heat-treated at 580 °C for 3 h and 850 °C for 8 h. Later the stoichiometric amount of SmAs, RuO 2 (Alfa Aesar 99.9%) Fe 2 O 3 (Alfa Aesar) and Fe (Alfa Aesar 99.2%) were weighed, mixed, ground thoroughly and palletized in rectangular form in a glove box in high purity Ar atmosphere. The pallet sealed in an evacuated quartz tube and heated at 1150 °C for 30 h. Finally, the quartz ampoule was allowed to cool naturally at room temperature. The X-ray diffraction patterns of the compound were taken on Rigaku Miniflex II diffractometer using Cu K a . The resistivity measurement was carried out by con- ventional four-probe method on a close cycle refrigerator in tem- perature range 22–300 K. The room temperature powder X-ray diffraction (XRD) pattern and Rietveld analysis are shown in Fig. 1. Both the compounds have ZrCuSiAs-type structure and fitted with space group P4/ nmm. The samples are crystallized in single phase but some weak 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.11.015 * Corresponding author. Tel.: +91 9999793867; fax: +91 11 45609310. E-mail address: vajpaya@nplindia.ernet.in (A. Vajpayee). Physica C 470 (2010) S491–S492 Contents lists available at ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc