L Journal of Alloys and Compounds 306 (2000) 47–55 www.elsevier.com / locate / jallcom Magnetic ordering in TbMn Cr Sn ( x 51, 2) compounds studied by 6 2x x 6 neutron diffraction and magnetic measurements a, b b c * ´ P. Schobinger-Papamantellos , G. Andre , J. Rodriguez-Carvajal , H.G.M. Duijn , c K.H.J. Buschow a ¨ ¨ Laboratorium f ur Kristallographie, ETHZ, CH-8092 Zurich, Switzerland b ´ Laboratoire Leon Brillouin ( CEA-CNRS), Centre d’ Etudes de Saclay, 91191, Gif-sur-Yvette, France c Van der Waals-Zeeman Institute, University of Amsterdam, 1018 XE Amsterdam, The Netherlands Received 4 February 2000; accepted 16 February 2000 Abstract The magnetic behaviour of the TbMn Cr Sn (x51, 2) compounds has been studied by neutron diffraction and magnetic 62x x 6 measurements. Both compounds exhibit a uniaxial ferromagnetic moment arrangement for both magnetic (R and Mn) sublattices, which order simultaneously and are coupled antiferromagnetically over the entire ordered regime below T . A spin reorientation transition C occurs at lower temperatures ( T ). The magnetic phase diagram comprises three regions. In the high temperature range T –T the t t C magnetic moments are confined to the basal plane. In the intermediate region T –T spanning about 40–50 K the moments rotate smoothly t i by 90 K. In the low temperature range 1.5 K–T the magnetic moments of both sublattices point into the c-direction. The ordered moment i values at 1.5 K are 8.62(5) m and 8.9(1) m per Tb atom and 2.09(2) m and 1.88(3) m per (Mn / Cr) atom for the two compounds B B B B TbMn CrSn and TbMn Cr Sn , respectively. Alloying with the almost non-magnetic Cr leads to a linear decrease of the ordering and of 5 6 4 2 6 the spin reorientation temperatures.  2000 Elsevier Science S.A. All rights reserved. Keywords: Rare earth compounds; Magnetically ordered materials; Neutron diffraction; Magnetization; Phase transition 1. Introduction TbMn Sn display a ferromagnetic type transition at T 5 6 6 c 423 K with a simultaneous ordering of the two sublattices The crystal structure and the magnetic properties of the and a second apparent magnetic transition at lower tem- RMn Sn (R5Sc, Y, Gd–Tm, Lu) compounds were first perature, T 5330 K. The latter could be related to a 6 6 t reported by Malaman et al. [1] and Venturini et al. [2]. The reorientation of the magnetisation from an easy plane crystal structure, isomorphic to HfFe Ge hexagonal type (001) to an easy axis [001] with decreasing temperature. 6 6 ( P6 / mmm space group), can be viewed as consisting of a The nature of the second transition was disclosed from the stacking of hexagonal R layers comprising Sn atoms and temperature-dependent magnetisation measurements made ´ Mn Kagome nets in the sequence Mn–R–Mn–Mn–R–Mn on a pseudo single crystal of TbMn Sn with the field 6 6 along the c axis. Two Sn layers separate the successive Mn applied parallel and perpendicular to the c-axis [2]. Also layers. The R atoms are located at the 1b site: (000), Mn at characteristic of a spin reorientation transition is the the 6i site: (1/2, 0, 0.247) and Sn at the 2e sites: (0, 0, observed hysteresis loop with the largest coercive field (11 0.336), 2d : (1/3, 2/3, 1/2) and 2c: (1/3, 2/3, 0). This kOe) at 4.2 K of the series. The magnetic structure of atomic arrangement gives rise to a large number of R–R, TbMn Sn studied by neutron diffraction in the range 2 to 6 6 Mn–Mn and R–Mn competing interactions involving 300 K [3] was found to be collinear with the moments of complex ordering types and phase transitions and has led the two sublattices coupled antiferromagnetically in good to several ongoing investigations [3–11]. agreement with the magnetic measurements. At 2 K the According to Ref. [2] the magnetic measurements on magnetic moments of both sublattices point to the [001] direction, while at 300 K they already deviate by 158 from the c-axis. A more recent communication [8] completes the *Corresponding author. description of the high temperature behaviour. E-mail address: nelly@ethz.erdw.kristal.ch (P. Schobinger-Papaman- tellos) High field free-powder magnetic measurements for low 0925-8388 / 00 / $ – see front matter  2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388(00)00777-5