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 ∘C, is tetragonal CaBe2Ge2 type [P4/nmm, tP  10, a=4.528(1)Å, c=11.370(2)Å, V=233.1(1)Å3]; the low-temperature form (LT-EuZn2Sn2), stable below 645 ∘C, is monoclinic LaPt2Ge2 type [P21, mP  10, a=4.596(1)Å,b=4.552(1)Å,c=11.331(2)Å,β=90.85(1)∘,V=237.0(1)Å3]. The two structures are closely related, the monoclinic structure being a deformation derivative of the tetragonal one. Detailed magnetization, heat capacity, electrical resistivity and 151151Eu-Mössbauer measurements have been carried out on the two polymorphs. In both forms, the Eu ions are in the divalent state, 4f7−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 151151Eu-Mössbauer spectra of the two stannides are practically identical, both in the paramagnetic and in the magnetically ordered state.