Crystal structure and magnetic ordering in dimorphic EuZn2Sn2

We report on the synthesis and magnetic properties of the new Eu-based intermetallic EuZn2Sn2. The compound shows dimorphism; its formation and dimorphic nature have been investigated by powder and single crystal X-ray diffractometry, as well as by differential thermal analyses. The high-temperature form (HT-EuZn2Sn2), stable above 645 degrees C, is tetragonal CaBe2Ge2 type [P4/nmm, tP10, a = 4.528(1) angstrom. c = 11.370(2) angstrom, V = 233.1(1) angstrom(3) ]; the low-temperature form (LT-EuZn2Sn2), stable below 645 degrees C, is monoclinic LaPt2Ge2 type [P2(1), mP10, a = 4.596(1) angstrom. b = 4.552(1) angstrom, c = 11.331(2) angstrom, beta = 90.85(1)degrees, V = 237.00) angstrom 3 ]. The two structures are closely related, the monoclinic structure being a deformation derivative of the tetragonal one. Detailed magnetization, heat capacity, electrical resistivity and 151 Eu-M6ssbauer measurements have been carried out on the two polymorphs. In both forms, the Eu ions are in the divalent state, 4f(7) - EU2+, and, as inferred from the peak in the susceptibility, order antiferromagnetically at 10.4 and 9.8 K in HT- and LT-EUZn2Sn2, respectively. The Eu-151-Mossbauer spectra of the two stannides are practically identical, both in the paramagnetic and in the magnetically ordered state. (C) 2008 Elsevier Ltd. All rights reserved.