Crystal structure and magnetic properties of ordered phases in the Eu-Cu-Sn system

Three new compounds in the ternary Eu-Cu-Sn system were identified and their crystal structure determined by powder Guinier patterns and single crystal diffractometer methods. EuCu9Sn4: tetragonal, I4/mcm, tI56, a = 8.633(2) Å, c = 12.425(2) Å, LaFe9Si4-type (ordered derivative of the NaZn13 structure); EuCu4Sn2: tetragonal, I4/mcm, tI28, a = 8.123(2) Å, c = 7.792(1) Å, with a structure related to the KAu4Sn2-type; EuCuSn2: orthorhombic, Cmcm, oS16, a = 4.4923(8) Å, b = 19.427(4) Å, c = 4.4983(8) Å, CeNiSi2-type. The three structures are ordered and no deficiency of copper is found in EuCuSn2. Measurements of the electrical resistivity, heat capacity, magnetization and 151Eu Mössbauer spectroscopy were made for the above compounds and for the previously discovered Eu3Cu8Sn4. Antiferromagnetic transitions near 6 and 11 K occur in Eu3Cu8Sn4 and EuCuSn2, respectively, while EuCu9Sn4 orders ferromagnetically near 10 K. Eu ions are likewise divalent in EuCu4Sn2 and are in a magnetically ordered state at 4.2 K as inferred from the magnetic hyperfine field-split 151Eu Mössbauer spectrum obtained at that temperature.