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, tP10, a = 4.528 ( 1 ) Å , c = 11.370 ( 2 ) Å , V = 233.1 ( 1 ) Å 3 ]; the low-temperature form (LT-EuZn2Sn2), stable below 645 ∘C, is monoclinic LaPt2Ge2 type [P21, mP10, a = 4.596 ( 1 ) Å , b = 4.552 ( 1 ) Å , c = 11.331 ( 2 ) Å , β = 90.85 ( 1 ) ∘ , V = 237.0 ( 1 ) Å 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-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 151 Eu-Mössbauer spectra of the two stannides are practically identical, both in the paramagnetic and in the magnetically ordered state.