Marcel Kersting

Reversible table-like magnetocaloric effect in Eu4PdMg over a very large temperature span

The magnetic properties and magnetocaloric effect (MCE) of the ternary intermetallic compound of Eu4PdMg have been investigated. Eu4PdMg has a very magnetic field sensitive magnetic phase transition, resulting in a reversible, table-like MCE over a broad temperature range. For the magnetic field changes of 0–5 T and 0–7 T, the maximum values of magnetic entropy change (−ΔSMmax) are 5.5 J kg−1 K−1 and 7.2 J kg−1 K−1, respectively, the corresponding refrigeration capacity (RC) are 977 J kg−1 and 1346 J kg−1. The RC values are obviously larger than those of some potential magnetic refrigerant materials at similar temperature region, making Eu4PdMg attractive for magnetic refrigeration.

Synthesis and structure of RE2RuMg2 (RE = Dy, Ho, Er, Tm, Lu) – i5 superstructures of the bcc packing

Abstract The isotypic intermetallic compounds RE2RuMg2 (RE = Dy, Ho, Er, Tm, Lu) were synthesized from the elements in sealed niobium tubes in a muffle furnace with different annealing sequences. The polycrystalline samples were characterized through Guinier powder patterns. The structure of Er2RuMg2 was refined on the basis of single-crystal X-ray diffractometer data: ordered Os2Al3 type, I4/mmm, a = 338.44(5), c = 2029.4(4) pm, wR2 = 0.0237, 234F2 values, and 10 variables. The Er2RuMg2 structure is an i5 superstructure of the bcc packing with complete ordering of the erbium, ruthenium, and magnesium atoms. Layers of compressed, ruthenium-centered erbium cubes (290 pm Er-Ru) alternate with layers of edge-sharing magnesium tetrahedra (311 and 338 pm Mg-Mg); a new type of magnesium substructure. Temperature dependent magnetic susceptibility studies confirm the stable trivalent ground states of the rare earth elements. Lu2RuMg2 is a Pauli paramagnet and the remaining four compounds show Curie paramagnetism. Dy2RuMg2 and Ho2RuMg2 are accompanied by antiferromagnetic ordering at 8.9(1) and 3.6(1) K, respectively.

A 25Mg, 89Y and 115In solid state MAS NMR study of YT2X and Y(T0.5T′0.5)2X (T/T′ = Pd, Ag, Au; X = Mg, In) Heusler phases

Yttrium-transition metal-magnesium (indium) Heusler phases YPd2Mg, YPd2In, YAg2Mg, YAg2In, YAu2Mg, and YAu2In and their quaternary compounds (solid solutions) Y(Pd0.5Ag0.5)2Mg, Y(Pd0.5Ag0.5)2In, Y(Pd0.5Au0.5)2Mg, Y(Pd0.5Au0.5)2In, Y(Ag0.5Au0.5)2Mg and Y(Ag0.5Au0.5)2In were synthesized from the elements in sealed niobium ampoules in a high-frequency furnace or by arc-melting, respectively. All compounds crystallize with the cubic MnCu2Al type structure (Heusler phase), space group Fm3[combining macron]m. The structure of Y(Ag0.39Au0.61)2Mg was refined from single crystal X-ray diffractometer data: a = 689.97(5) pm, wR2 = 0.0619, 52 F2 values, 6 parameters. Magnetic susceptibility measurements show Pauli paramagnetic behavior for all samples. The compounds were investigated by 25Mg, 89Y and 115In solid state MAS NMR spectroscopy. Large positive resonance shifts are observed for all nuclei. A review of the present data in the context of literature data on isotypic Heusler phases with Cd and Sn indicates that the 89Y shifts show a correlation with the electronegativity of the main group atoms (Mg, Cd, In, Sn). The solid solutions Y(Ag1-xTx)2Mg (x = 0.1, 0.25, 0.33, 0.5; T = Pd, Au) clearly show Vegard-like behavior concerning their lattice parameters, and their main group element resonance shifts arising from spin and orbital contributions are close to the interpolated values of the corresponding end-member compounds.

The magnesium intermetallics RE2RuMg (RE = Sc, Y, Er, Tm, Lu) – i2 superstructures of the CuAu type

Abstract The magnesium intermetallics RE2RuMg (RE = Sc, Y, Er, Tm, Lu) were synthesized by melting of the elements in sealed niobium ampoules followed by different annealing sequences in muffle furnaces. The samples were characterized by powder X-ray diffraction. The structure of Sc2RuMg (Pt2ZnCd type, P4/mmm, a = 326.07(6), c = 760.9(2) pm, wR2 = 0.0749, 138 F2 values, 9 variables) was refined from single crystal diffractometer data. Sc2RuMg is an i2 superstructure of the CuAu type with alternating and tetragonally distorted Ru@Sc8 and Mg@Sc8 cubes.

Magnesium-rich Intermetallics RE3RuMg7 (RE=Y, Nd, Dy, Ho) – Rows of Condensed Ru@RE6/2 Octahedra in Magnesium Matrices

The magnesium-rich intermetallic phases RE3RuMg7 (RE=Y, Nd, Dy, Ho) have been synthesized from the elements in sealed niobium ampoules and subsequently characterized by powder X-ray diffraction. The structure of the dysprosium compound was refined on the basis of single-crystal X-ray diffractometer data: Ti6Sn5 type, P63=mmc, a=1019.1(2), c=606.76(9) pm, wR2=0.0159, 439 F2 values, 19 variables. The Mg3 site shows a small degree of Mg3=Dy mixing, leading to the composition Dy3:03RuMg6:97 for the investigated crystal. The striking structural motifs in the Dy3RuMg7 structure are rows of face-sharing Ru@Dy6 octahedra and corner-sharing Mg2@Mg8Dy4 icosahedra. The rows of octahedra form a hexagonal rod-packing, and each rod is enrolled by six rows of the condensed icosahedra. Temperature-dependent magnetic susceptibility measurements of Dy3RuMg7 show Curie-Weiss behavior with an experimental magnetic moment of 10.66(1) µB per Dy atom. Antiferromagnetic ordering is detected at TN =27.5(5) K. The 5 K isotherm shows a metamagnetic transition at a critical field of HC =40 kOe Graphical Abstract Magnesium-rich Intermetallics RE3RuMg7 (RE=Y, Nd, Dy, Ho) – Rows of Condensed Ru@RE6/2 Octahedra in Magnesium Matrices

CaTMg2 and CaTCd2 (T = Rh, Pd, Pt) with YPd2Si-type structure

The intermetallic calcium compounds CaTMg2 and CaTCd2 (T =Rh, Pd, Pt) were obtained by high-frequency melting of the elements in sealed niobium ampoules or through reactions in muffle furnaces. The polycrystalline samples were characterized by powder X-ray diffraction. They crystallize with a site occupancy variant of YPd2Si, a ternary ordered version of Fe3C. The structures of CaPdMg2 and CaPdCd2 were refined from single-crystal diffractometer data: Pnma, a=792.2(2), b=803.4(2), c=572.0(1) pm, wR2=0.0663, 1621 F2 values, 24 variables for Ca0:94PdMg2:06 and a=794.6(2), b=809.5(3), c=554.7(2) pm, wR2=0.0301, 819 F2 values, 23 variables for CaPdCd2. A small range of homogeneity was observed for Ca1-xPdMg2+x. The magnesium and cadmium atoms build up three-dimensional tetrahedral substructures (306 - 327 pm Mg-Mg and 307 - 317 pm Cd-Cd) that resemble hexagonal diamond, lonsdaleite. Together with the palladium atoms one obtains three-dimensional, covalently bonded [PdMg2] and [PdCd2] networks which leave cages for the calcium atoms. The latter are bonded to these networks via shorter Ca-Pd contacts (298 - 319 pm in Ca0:94PdMg2:06 and 295 - 312 pm in CaPdCd2). The course of the interatomic distances is in line with calculated overlap populations. The CaPdMg2, SrPdMg2 and CaRhIn2 structures are all derived from a CaIn2-related subcell by an ordered filling of transition metal atoms into trigonal prisms. This leads to different herringbone patterns for the networks of puckered and elongated hexagons of magnesium and indium atoms. Graphical Abstract CaTMg2 and CaTCd2 (T =Rh, Pd, Pt) with YPd2Si-type Structure

Rare earth-ruthenium-magnesium intermetallics

Abstract Eight new intermetallic rare earth-ruthenium-magnesium compounds have been synthesized from the elements in sealed niobium ampoules using different annealing sequences in muffle furnaces. The compounds have been characterized by powder and single crystal X-ray diffraction. Sm9.2Ru6Mg17.8 (a=939.6(2), c=1779(1) pm), Gd11Ru6Mg16 (a=951.9(2), c=1756.8(8) pm), and Tb10.5Ru6Mg16.5 (a=942.5(1), c=1758.3(4) pm) crystallize with the tetragonal Nd9.34Ru6Mg17.66 type structure, space group I4/mmm. This structure exhibits a complex condensation pattern of square-prisms and square-antiprisms around the magnesium and ruthenium atoms, respectively. Y2RuMg2 (a=344.0(1), c=2019(1) pm) and Tb2RuMg2 (a=341.43(6), c=2054.2(7) pm) adopt the Er2RuMg2 structure and Tm3Ru2Mg (a=337.72(9), c=1129.8(4) pm) is isotypic with Sc3Ru2Mg. Tm3Ru2Mg2 (a=337.35(9), c=2671(1) pm) and Lu3Ru2Mg2 (a=335.83(5), c=2652.2(5) pm) are the first ternary ordered variants of the Ti3Cu4 type, space group I4/mmm. These five compounds belong to a large family of intermetallics which are completely ordered superstructures of the bcc subcell. The group-subgroup scheme for Lu3Ru2Mg2 is presented. The common structural motif of all three structure types are ruthenium-centered rare earth cubes reminicent of the CsCl type. Magnetic susceptibility measurements of Y2RuMg2 and Lu3Ru2Mg2 samples revealed Pauli paramagnetism of the conduction electrons.

Large Reversible Magnetocaloric Effect Around Liquid Hydrogen Temperature in Er 4 PdMg Compound

The magnetic properties and the magnetocaloric effect (MCE) in the Er₄PdMg compound have been investigated by magnetization and heat capacity measurements. The compound undergoes a second-order magnetic phase transition from a paramagnetic to a ferromagnetic state at Curie temperatures of T_C ~ 21.5 K, which is just above the liquid hydrogen temperature (20.3 K). A large reversible MCE was observed. The maximum values of magnetic entropy change (-ΔS^max_M ) and adiabatic temperature change (ΔT^max_ad ) for Er₄PdMg under a field change of 0-7 T are 20.6 J/kg K and 5.5 K, respectively. The corresponding value of relative cooling power (RCP) was evaluated to be 742 J/kg. The large reversible MCE together with considerable RCP values makes the Er₄PdMg compound attractive for magnetic refrigeration.

Intermetallic magnesium compounds RE2RuMg3 (RE = Dy, Ho, Er, Tm, Lu) and RE3Ru2Mg (RE = Sc, Er, Lu) with bcc Superstructures

Abstract The intermetallic magnesium compounds RE2RuMg3 (RE = Dy, Ho, Er, Tm, Lu) and RE3Ru2Mg (RE = Sc, Er, Lu) were synthesized from the elements in sealed niobium tubes in muffle or induction furnaces using different annealing sequences. The polycrystalline RE2RuMg3 and RE3Ru2Mg samples were characterized through Guinier powder patterns. The structures of Er2RuMg3 and Sc3Ru2Mg were refined on the basis of single-crystal X-ray diffractometer data: new type, P4/mmm, a = 336.71(9), c = 1234.6(7) pm, wR = 0.0327, 240 F values, 12 variables for Er2RuMg3 and a = 324.67(6), c = 1077.2(3) pm, wR = 0.0345, 273 F values, 12 variables for Sc3Ru2Mg. The Er2RuMg3 and Sc3Ru2Mg structures are i3 superstructures of the CuAu type and thus belong to the large family of ordered bcc derivatives. The fundamental building units are distorted ErRu, ScRu, ScMg, and ErMg cubes. The magnesium-rich phase Er2RuMg3 has a pronounced Mg substructure (314–337 pm Mg–Mg) with distorted cuboctahedral coordination. This substructure is compared to other magnesium-rich compounds. Temperature dependent magnetic susceptibility studies show Curie-Weiss paramagnetism for RE2RuMg3 (RE = Dy, Ho, Er, Tm) with experimental magnetic moments close to the RE3+ free ion values. The compounds exhibit antiferromagnetic ordering at Néel temperatures of 6.5(1), 3.6(5), 3.5(5), and 5(1) K, respectively. Metamagnetic transitions underline the stable antiferromagnetic ground states. Lu2RuMg3 is a Pauli paramagnet.

Magnesium and cadmium in covalently bonded networks: synthesis and structure of AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) with TiNiSi type structure and the solid solution Yb2–xPtMgx

Abstract The equiatomic intermetallic compounds AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) and the whole solid solution Yb2-xPtMgx were synthesized from the elements in sealed niobium tubes in a high-frequency or a muffle furnace. All samples were characterized on the basis of their powder X-ray diffraction patterns. The structures of SrAuCd, CaPdCd, CaPtCd, CaPdMg, SrPtMg, CaAg1.017Mg0.983, SrAg1.032Mg0.968, and Yb1.792PtMg0.208 were refined on the basis of single-crystal X-ray diffractometer data. Some of the crystals showed small homogeneity ranges. All compounds crystallize with the orthorhombic TiNiSi type structure, space group Pnma. The crystal chemistry is briefly discussed and variations in chemical bonding as a result of the electronegativity of the transition metal are described.