Stefan Linsinger

The solid solution Gd2NixCu2−xMg: Large reversible magnetocaloric effect and a drastic change of the magnetism by substitution

Various samples of the solid solution Gd2NixCu2-xMg were synthesized from the elements in sealed tantalum ampoules in an induction furnace. All members crystallize with the tetragonal Mo2FeB2 type structure, space group P4/mbm, and they were characterized on the basis of Guinier powder patterns and energy dispersive X-rays analyses. The lattice parameters decrease with increasing nickel content in a Vegard-like manner. The Gd2NixCu2-xMg samples show Curie Weiss behavior with slightly higher magnetic moment values than the theoretical one for a free Gd3+ ion. The substitution of copper by nickel has a drastic influence on the magnetism and magnetic ordering temperature. For Gd2Ni0.5Cu1.5Mg a temperature induced FM -> AFM order-to-order transition was observed, whereas Gd2Ni1.0Cu1.0Mg is a metamagnet with H-Cr of about 8 kOe at 5 K. For both compounds, a large reversible magnetocaloric effect (MCE) near their ordering temperatures occurs. The values of the maximum magnetic entropy change -Delta S-M(max) reach 9.5 and 11.4 J kg(-1) K-1 for the field change of 5 T with no obvious hysteresis loss around 65 K for Gd2Ni0.5Cu1.5Mg and Gd2Ni1.0Cu1.0Mg, respectively. The corresponding relative cooling power with 688 and 630 J kg(-1) is relatively high as compared to other MCE materials in that temperature range. These results indicate that Gd2NixCu2-xMg could be a promising system for magnetic refrigeration at temperatures below liquid N-2

Intermediate-valent Ce23Ru7Mg4 and RE23Ru7Mg4 (RE = La, Pr, Nd) with Pr23Ir7Mg4-type Structure

The rare earth-rich magnesium compounds RE23Ru7Mg4 (RE = La, Ce, Pr, Nd) were synthesized from the elements in sealed tantalum ampoules in an induction furnace. They crystallize with the hexagonal non-centrosymmetric Pr23Ir7Mg4-type structure, space group P63mc. The structures of La23Ru6.88(1)Mg4 (a = 1017.7(4), c = 2286.5(5) pm, wR2 = 0.0277, 2708 F2, 71 variables), Ce23Ru7Mg4 (a = 993.5(3), c = 2243.9(8) pm, wR2 = 0.0573, 2268 F2, 70 variables), and Pr23Ru7Mg4 (a = 996.8(3), c = 2241.5(6) pm, wR2 = 0.0492, 2565 F2, 70 variables) have been refined from single-crystal diffractometer data. The structures are built up from complex threedimensional networks of edge- and corner-sharing RE6Ru trigonal prisms. Cavities within these networks are filled by slightly elongated Mg4 tetrahedra (311 - 315 pm in Pr23Ru7Mg4) and RE6 octahedra. The cerium compound has an a parameter which is even smaller than that of Nd23 Ru7Mg4, indicating intermediate-valent cerium. This was confirmed by magnetic susceptibility measurements. Ce23Ru7Mg4 shows an average, reduced magnetic moment of 2.01 μB/Ce atom. Pr23Ru7Mg4 contains stable trivalent praseodymium (3.64 μB/Pr atom) Graphical Abstract Intermediate-valent Ce23Ru7Mg4 and RE23Ru7Mg4 (RE = La, Pr, Nd) with Pr23Ir7Mg4-type Structure

Intermediate-valent Cerium in CeRu2Mg5

The magnesium-rich compound CeRu2Mg5 was synthesized by high-frequency melting of the elements in a sealed tantalum ampoule. CeRu2Mg5 crystallizes with a new tetragonal structure type: P42/ncm, a = 961.1(1), c = 723.2(1) pm, wR2 = 0.0284, 481 F2 values and 25 variables. The striking structural motifs in CeRu2Mg5 are short Ce-Ru distances of 232 pm. Each cerium atom is connected to two ruthenium atoms within a three-dimensional [Ru2Mg5] network. CeRu2Mg5 has a pronounced magnesium substructure with short Mg-Mg distances in the range 302 - 341 pm. The short Ce-Ru distances are a consequence of the almost tetravalent character of the cerium atoms. Temperature-dependent magnetic susceptibility data show intermediate-valent behavior of the cerium atoms (0.9(1) μB per formula unit) and no magnetic ordering down to 3 K. Graphical Abstract Intermediate-valent Cerium in CeRu2Mg5

Ternary aurides RE4Mg3Au10 (RE=Y, Nd, Sm, Gd–Dy) and their silver analogues

Abstract The ternary aurides RE4Mg3Au10 (RE=Y, Nd, Sm, Gd–Dy) and their silver analogues were synthesized by induction melting of the elements in sealed niobium tubes. These intermetallic phases were characterized by powder X-ray diffraction. They crystallize with the Ca4In3Au10-type structure, which, from a geometrical point of view, is a ternary ordered version of Zr7Ni10 with the rare earth and magnesium atoms ordering on the four crystallographically independent zirconium sites. The structures of crystals from three differently prepared gadolinium samples were refined from single-crystal X-ray diffractometer data: Cmca, a=1366.69(3), b=998.07(4), c=1005.54(3) pm, wR2=0.0332, 1234 F2 values, 46 variables for Gd4.43Mg2.57Au10, a=1378.7(1), b=1005.3(1), c=1011.2(1) pm, wR2=0.0409, 1255 F2 values, 48 variables for Gd5.50Mg1.50Au10, and a=1350.2(5), b=995.5(1), c=1009.3(1) pm, wR2=0.0478, 1075 F2 values, 48 variables for Gd5.61Mg1.39Au10. All crystals show substantial Mg/Gd mixing on two sites. The gold atoms form a pronounced two-dimensional substructure with Au–Au distances of 278 to 297 pm in Gd4.43Mg2.57Au10. These gold blocks are condensed via magnesium atoms (278–315 pm Mg–Au). The gadolinium atoms fill larger cavities within the three-dimensional networks. The magnesium vs. gadolinium site preference is a consequence of the different coordination numbers of the cation sites. All phases show homogeneity ranges RE4+xMg3–xAg10 and RE4+xMg3–xAu10. The influence of the synthesis conditions is briefly discussed.

Chains of Condensed RuSm6/2 Octahedra in Sm3RuMg7 – A Ternary Ordered Version of the Ti6Sn5 Type

The magnesium-rich intermetallic compound Sm3RuMg7 was synthesized by induction melting of the elements. Single crystals were grown by slow cooling of the polycrystalline sample. The structure was characterized by powder and single-crystal X-ray diffraction: ordered Ti6Sn5 type, P63/mmc, Z = 2, a = 1034.1(2), c = 611.3(1) pm, wR2 = 0.0216, 399 F2 values and 19 parameters. The ruthenium atoms have slightly distorted octahedral samarium coordination. These RuSm6/2 octahedra (Ru-Sm 279 pm) are condensed via common faces leading to chains in the c direction which are arranged in the form of a hexagonal rod packing. Between these rods the Mg2 atoms build chains of face-sharing trigonal prisms. Alternately these prisms are centered by Mg3 or capped by Mg1 atoms on the rectangular faces. Within the magnesium substructure the Mg-Mg distances range from 303 to 335 pm. The Mg3 site shows slight mixing with samarium, leading to the composition Sm3.16RuMg6.84 for the investigated crystal. The compounds RE3RuMg7 (RE = Gd, Tb) are isotypic. Graphical Abstract Chains of Condensed RuSm6/2 Octahedra in Sm3RuMg7 – A Ternary Ordered Version of the Ti6Sn5 Type

Intermetallic Magnesium CompoundsRE 2 Ni 2 Mg 3 (RE=Gd, Dy-Tm, Lu) with Tb 2 Ni 2 Mg 3 -type Structure

New intermetallic magnesium compounds RE2Ni2Mg3 (RE = Gd, Dy-Tm, Lu) were synthesized from the elements by induction melting. They are isotypic with Tb2Ni2Mg3. The structure of Gd2Ni2Mg3 was refined from X-ray powder data: Cmmm, a = 398.7(1), b = 2121.9(7), c = 368.39(9) pm, RB = 7.49%, 3800 data points, 23 parameters. The RE2Ni2Mg3 intermetallics are intergrowth variants of AlB2- and CsCl-related slabs. Gd2Ni2Mg3 is a Curie-Weiss paramagnet above 75 K with an experimental magnetic moment of μeff = 8.16(1) μB /Gd atom. Antiferromagnetic ordering sets in at TN = 42.0(5) K. Graphical Abstract Intermetallic Magnesium Compounds RE2Ni2Mg3 (RE =Gd, Dy–Tm, Lu) with Tb2Ni2Mg3-type Structure