JOURNAL OF SOLID STATE CHEMISTRY 137, 249 — 254 (1998) ARTICLE NO. SC977723 Spin-Glass-like Behavior in the Selenide Cr 2 Sn 3 Se 7 F. Bode´nan, V. B. Cajipe, 1 M. Danot, and G. Ouvrard Institut des Mate ´ riaux de Nantes, Laboratoire de Chimie des Solides, UMR 6502, 2 rue de la Houssinie % re, BP 32229, 44322 Nantes Cedex 3, France Received June 23, 1997; in revised form November 23, 1997; accepted December 4, 1997 Magnetic measurements show that monoclinic Cr 2 Sn 3 Se 7 ex- hibits many of the defining characteristics of a spin glass below 30 K. Low-temperature 119 Sn Mo ¨ ssbauer spectroscopy and neu- tron powder diffraction data are also consistent with the occur- rence of short-range magnetic order. This behavior is discussed in relation to the probable nature of magnetic interactions and the origin of randomness in Cr 2 Sn 3 Se 7 .  1998 Academic Press Key Words: chromium selenide; spin glass; 119 Sn Mo ¨ ssbauer spectroscopy. INTRODUCTION Within the past 15 years the study of spin glass behavior, first detected in dilute metallic alloys, has been extended to a large number of more concentrated and nonmetallic sys- tems. The occurrence of a transition in which spin orienta- tions freeze without establishing long-range order requires that the magnetic sublattice exhibit a high degree of random- ness and the spins be subject to strongly competing interac- tions. These conditions are satisfied in some amorphous compounds. More typically, however, spin glass or other frozen spin behavior has been observed in materials with crystalline structures characterized by some combination of magnetic site disorder and a geometry favoring frustration (1). Recently, our search for ternary chromium chalcogenides containing low-dimensional magnetic sublattices led to the synthesis and the structural characterization of a new sele- nide with the formula Cr  Sn  Se  (Cr  Sn  SnSe  ). There are two variants of this compound, one with a monoclinic (space group P2  /m) (2) and the other with an orthorhombic (Pnma) [3] structure. Each may be described in terms of edge-sharing selenium octahedra forming [M  Se  ] ribbons and [MSe  ] sheets as shown in Fig. 1a for the monoclinic phase (a"12.765(5) A s , b"3.835(2) A s , and c"11.785(4) A s , "105.21°). The octahedral sites M form a triangular net- work and are statistically occupied by the magnetic Cr and diamagnetic Sn cations in a 2 : 1 ratio (Fig. 1b); the tunnels defined by the sheets and ribbons are filled by the Sn.  To whom correspondence should be addressed. Initial dc magnetic susceptibility measurements revealed a maximum in the 20—30 K range for both forms of Cr  Sn  Se  (2, 3). This feature was found to be sensitive to whether cooling is done with or without an applied field. Moreover, the temperature at which this maximum appears in the orthorhombic phase was shown to be field-dependent. Such observations are consistent with a freezing in of mag- netic disorder and a low-temperature superparamagnetic or spin glass state has been suggested for these selenides [3]. In this paper, we present results of new magnetic measurements as well as Sn Mo¨ssbauer spectroscopy and neutron diffraction experiments performed on mon- oclinic Cr  Sn  Se  . The data are discussed in relation to the peculiarities of the Cr sublattice and the hypothesis of spin glass behavior. EXPERIMENTAL Monoclinic Cr  Sn  Se  was prepared via solid-state reac- tion as previously described (2). Dc magnetic measurements were carried out using a Quantum Design SQUID mag- netometer on two samples: 13 mg of selected needlelike crystals and 60 mg of powder sieved to 20 m and verified pure by X-ray diffraction and scanning electron microscopy analysis of polished sections. Ac magnetic susceptibility measurements were performed with a Lakeshore suscep- tometer on 100 mg of the powder sieved to 20 m. Sn Mo¨ssbauer spectra were obtained with a constant-acceler- ation spectrometer using a symmetric sawtooth vibrator; isomer shifts were measured relative to CaSnO  at 300 K. Neutron diffraction experiments were carried out on the G4.1 multidetector powder diffractometer at the Labora- toire Le´ on Brillouin (CEA-Saclay, France) using 5 g of pow- der sieved to 100 m; data were collected with "2.422 A s at 5(2(85° and in 0.1° steps. RESULTS Magnetic Measurements The thermal evolution of the inverse dc magnetic suscepti- bility of monoclinic Cr  Sn  Se  , corrected for diamagnetism, 249 0022-4596/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.