Journal of Magnetism and Magnetic Materials 70 (1987) 391-392 391 North-Holland, Amsterdam MAGNETIC AND TRANSPORT PROPERTIES OF C%Sb AND Ce2Bi A. ISOBE, A. OCHIAI, S. ONODERA*, K. YAMADA, M. KOHGI, Y. ENDOH, T. SUZUKI and T. KASUYA Department of Physics, Faculty of Science. Tohoku UniversiO,, Sendai 980, Japan * Sendai National College of Technologt,, Ayashi. M~vagi, 989-31, Japan Magnetic susceptibility, electrical resistivity and neutron diffraction measurements of Ce2Sb and Ce2Bi are reported. A possible valence fluctation for Ce atoms in the metal sheets with a very short inner plane distance is discussed. Ce2Sb and Ce2Bi crystallize in the two dimen- sional Ti2Bi type of tetragonal structure (space group I4/mmm) [1]. Main features of this crystal structure are summarized as follows. There are two sites of Ce atoms in the unit cell. Cel lies in the mirror plane and their mutual distances within the planer metal sheet is extremely short (3.20 A) is compared with those of metallic valence fluctuating materials such as a-Ce (3.41 A) and CeN (3.55 A). On the other hand, the distances between the Ce2 atoms and between Ce2 and Sb atoms are nearly same as those of CeSb. Thus a question arises whether the Cel atoms in the metal sheets are in valence fluctuating or mag- metic states. In order to make this point clear we performed magnetic suceptibility, electrical resis- tivity and neutron diffraction measurments. Polycrystalline samples were synthesized first in a closed silica tube at about 500°C and then heated in a sealed molibudenum crucible at about ll00°C for one week. Single crystals of Ce2Sb were grown by some sorts of flux method from off stoichiometric starting materials keeping the tem- perature 1300°C in the sealed molibudenum crucible for two weeks. This method has been successfully performed to obtain single crystals of Sm4As 3 and Sm4Bi 3 [2]. The sample dimension is about 5 × 3 × 2 mm 3. These samples are easily destroyed in air, so these should be treated in a clean glove box. The neutron diffraction measure- ment on polycrystalline samples was performed by the high resolution powder spectrometer (HRP) installed in the pulsed neutron source in KEK. The temperature dependence of the magnetic susceptibility of the polycrystalline sample (Xpob) shows a transition to a supposed antiferromag- netic state with T N = 9.5 K for Ce2Sb and 15 K for CezBi, respectively, as shown in fig. 1 In this figure, the result of Xll, parallel to the c-axis, for the single crystal Ce2Sb is also shown. The mo- ment is thought to be aligned in the c-plane. Inverse susceptibility vs. temperature are shown in fig. 2 for both polycrystal Ce2Sb and Ce2Bi. A kink around 180 K in Ce2Sb is due to a crystal structure transformation. For C% Bi, we could ob- tain #err= 2.4/, B and 0p = -52 K from the slope of 1/X vs. T between 70 to 200 K, while for polycrystal Ce2Sb #err = 2-4/IB and 0p =-57 K from the deta above 150 K. Temperature dependence of resistivity of single 0.~ 0 ~o.1 /",, ! + L -o 5:.2", oo~:po -%../ "-. . .°-'/ ~ o. ¢, /e 0 o ~ 1'o 1~ T(K) Fig. 1. Temperature dependence of magnetic susceptibility for polycrystal CezSb is shown by crosses, that for single crystal Ce2Sb parallel to c-axis by open circles and that for poly- crystal Ce2Bi by closed circles. 0304-8853/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)