K. Hiebl

Magnetic properties and structural chemistry of ternary silicides (RE, Th, U) Ru2Si2 (RE=rare earth)

Abstract Ternary silicides (RE, Th, U)Ru 2 Si 2 have been synthesized from the elements. All the compounds (RE = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were found to be isotypic and to crystallize with the structure type of ThCr 2 Si 2 (ordered derivative of the BaAl 4 -type). The magnetic behavior of these alloys was studied in the temperature range 1.5 K T T > 300 K closely follow a typical Van Vleck paramagnetism of free RE 3+ -ions. In the case of CeRu 2 Si 2 susceptibilities are well described for 20 K T eff = 2.12 BM indicates a high percentage (85%) of Ce 3+ . SmRu 2 Si 2 yields an effective moment μ eff = 0.54 BM, which compares reasonably well with the Hunds rule J = 5/2 ground level for free Sm + and a low-lying excited level with J = 7/2. For temperatures T > 15 K the magnetic susceptibility as a function of temperature follows the “Van Vleck behavior” for free Sm 3+ . At low temperatures ferromagnetic ordering was encountered for (Pr, Nd, Ho, Er, Tm)Ru 2 Si 2 , whereas antiferromagnetic ordering was observed for (Sm, Gd, Tb, Dy)Ru 2 Si 2 . The ordering temperatures are generally below 55 K. No superconductivity was found for temperatures as low as 1.8 K.

On the crystal structure and magnetic properties of the ternary rare earth compounds RETSb2 with RE≡rare earth and T≡Ni, Pd, Cu and Au

Abstract Novel compounds RETSb 2 have been prepared and characterized for T  Cu (RE  rare earth from La to Lu), Ni (RE  La to Ho), Pd (RE  La to Tb) and Au (RE  La to Sm). From X-ray powder diffraction analyses all compounds were found to crystallize as the ZrCuSi 2 type. Magnetic susceptibilities were generally measured in the temperature range from 4 to 100 K. YCuSb 2 and LaTSb z are temperature-independent paramagnets. RETSb 2 compounds are found to order antiferromagnetically below T  20 K. PrPdSb 2 and TbPdSb 2 undergo metamagnetic transitions, whereas PrCuSb 2 and ErCuSb 2 are simple ferromagnets. The Sm-containing compounds are typical Van Vleck paramagnets owing to the closely spaced multiplets.

Al, Ga substitution in RE2Fe17 (RE=Ce,Pr,Nd): magnetic behavior of RE2Fe15(Al,Ga)2 alloys

Alloys with the composition RE2Fe17 and RE2Fe15X2 (X=Al,Ga) have been synthesized by the arc‐melting technique followed by an 125‐h anneal at 900–1000 °C in evacuated silica capsules. The new compound Nd2Fe15Ga2 is unstable below 800 °C, and is only obtained by quenching from above 900 °C. From x‐ray powder diffraction analysis all alloys except Pr2 Fe15 Ga2 were found to crystallize with the hexagonal Th2 Zn17 type; indications for a preferential occupation of the (6c) sites by the X atoms are small. Substitution of Al, Ga atoms generally leads to a large increase of the Curie temperature and of the magnetocrystalline anisotropy, thereby enhancing the remanence as well as the coercivity. These effects are a consequence of the strongly distance‐dependent exchange interactions of the Fe‐Fe and Fe‐RE coupling mechanisms. As for binary Pr2 Fe17 , the easy axis of magnetization for Pr2 Fe15 Al2 was found to be in the basal plane.

Structural chemistry and magnetic behaviour of ternary uranium gallides U{Fe,Co,Ni,Ru,Rh,Pd,Os,Ir,Pt}Ga5☆

The crystal structure of UCoGa5 was refined from single-crystal v-ray counter data. The space group was P4/mmm (No. 123) and the lattice parameters were a = 4.2357(5) A and c = 6.7278(9) A; v = 1. For 214 independent reflections (¦Fo¦>3σ) the reliability factor obtained was R − (Σ¦ΔF¦)/Σ¦Fo¦= 0.027. UCoGa5 crystallives with the HoCoGa5-type structure, combining structural units of the AuCu3- and PtHg2-type. Isotypic compounds were synthesived with all the group VIII elements: U{Fe,Co,Ni,Ru,Rh,Pd,Os,Ir,Pt}Ga5. Magnetic susceptibilities of the new compounds were studied in the temperature range of 80 K < T < 1100 K, and were found to be practically temperature independent. The crystal chemistry and magnetochemical behaviour of the new uranium gallides is discussed.

Formation, crystal chemistry and magnetism of compounds RE2TGe6, RE rare earth, T Pd, Pt, Cu, Ag and Au

Abstract Novel ternary compounds RE 2 TGe 6 (RE  Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb; T  Pd, Pt, Ag, Au) were synthesized by argon arc melting followed by a heat treatment at 600 or 800 °C for 150 h. From X-ray powder analysis all compounds were found to be isotypic with structure type Ce 2 CuGe 6 . Magnetic susceptibilities were measured for RE 2 CuGe 6 (RE  Ce, Pr, Nd, Sm) and Ce 2 PdGe 6 . All compounds exhibit antiferromagnetic ordering below 20 K. The paramagnetic effective moments agree with the values for tripositive RE ion moments. The Sm containing sample reveals typical Van Vleck type paramagnetism above the Neel point.

Crystal chemistry and magnetism of neodymium stannides including compounds of the structural series REnSn3n−2

The binary system Nd−Sn has been investigated employing X-ray powder techniques and magnetic susceptibility measurements up to 600 K and 6 T. The formation of the compounds Nd 5 Sn 3 , Nd 5 Sn 4 , Nd 11 Sn 10 , NdSn, “Nd 3 Sn 5 ,” and NdSn 3 has been confirmed. New phases Nd 2 Sn 5 , Nd 3 Sn 7 , and NdSn 2 have been observed and their crystal structures were found to be isotypic with the structure types of Ce 2 Sn 5 , Ce 3 Sn 7 , and NdSn 2 (ZrGa 2 ), respectively. Further representatives of the Ce 2 Sn 5 -, the Ce 3 Sn 7 -, and the NdSn 2 -type have been synthesized for La, Pr, and Sm. The lanthanum-containing compounds are diamagnets above 80 K. La 2 Sn 5 and LaSn 2 become superconducting at 5.4 and 3.6 K, respectively. Pr 2 Sn 5 and PrSn 2 exhibit metamagnetism, whereas Pr 3 Sn 7 is a weak ferromagnet. Nd 5 Sn 3 and Nd 3 Sn 5 are metamagnets with Neel temperatures T N =40 K and T N =14 K, respectively, whereas Nd 5 Sn 4 , Nd 11 Sn 10 , NdSn, and Nd 3 Sn 7 order ferromagnetically at 67, 75, 32, and 10.5 K, respectively. NdSn 2 , Nd 2 Sn 5 , and NdSn 3 prove to be antiferromagnets at low temperatures. For the new samarium stannides Sm 3 Sn 7 and SmSn 2 , peaks in the susceptibility curves at 20 and 32 K give evidence of antiferromagnetic spin structures.

Magnetism of ternary compounds RE6Fe13X; RE=Pr, Nd; X=Cu, Ag, Au, Zn, Cd, and Hg

Novel compounds RE6Fe13X (X=Cu, Ag, Au, Zn, Cd, Hg) have been synthesized by arc melting (Cu, Ag, Au) or by reaction sintering (Zn, Cd, Hg), followed by heat treatment at 550 or 600 °C up to 350 h in evacuated silica capsules. From room temperature x‐ray powder diffraction analyses the alloys were found to crystallize with the ordered Nd6Fe13Si type. The Curie point of all the compounds is found to lie around room temperature. Due to their low magnetization values a ferrimagnetic coupling within the Fe sublattice is suggested. A canted RE‐spin structure cannot be ruled out. 57Fe Mossbauer spectra were recorded from the samples with X=Ag and Au. Additionally, 197Au spectra were taken from the two Au‐containing compounds. The 57Fe spectra are composed of various subpatterns, originating from the different Fe sites and were found to be essentially unaffected by the specific element RE and X. In all cases under investigation the spectra could only be fitted under the assumption of an easy axis of magnetizatio...

Magnetism and structural chemistry of ternary silicides: (RE, Th, U)Pt2Si2 (RE = rare earth)

Abstract Ternary silicides (RE, U, Th)Pt2Si2 have been prepared from the elements. All the compounds (RE= Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and U, Th) were found to be isotypic and crystallize with the primitive tetragonal CePt2Si2-type structure closely related to the CaBe2Ge2-type. The magnetic properties of these alloys were studied in the temperature range 1.5 K 200 K. A nonmagnetic ground state is reflected from the magnetic susceptibility data of CePt2Si2, which are interpreted in terms of interconfiguration fluctuations (ICF). The magnetic results of SmPt2Si2 (μeff = 0.7 BM) compare well with the ideal Van Vleck behavior of Sm3+ ions with a J = 5 2 ground state and a low-lying excited first level J = 7 2 . At temperatures below 40 K antiferromagnetic ordering is found for (Gd, Tb, U)Pt2Si2; whereas in case of (Dy, Ho, Er, Tm)Pt2Si2 the onset of ferromagnetism is indicated below 4 K. None of the samples exhibited a superconducting transition above 1.8 K.

Magnetic behaviour of ternary silicides CeT2Si2 (T ≡ Ru, Rh, Pd, Os, Ir, Pt) and boron substitution in Ce{Ru, Os}2Si2−xBx

Abstract The ternary silicides CeT 2 Si 2 have been investigated with respect to crystal chemistry and magnetochemical behaviour. Ce{Ru, Rh, Pd, Os} 2 Si 2 crystallize with the body-centred tetragonal ThCr 2 Si 2 -type structure, whereas CePt 2 Si 2 and h-CeIr 2 Si 2 adopt the primitive tetragonal CePt 2 Si 2 -type structure and CaBe 2 Ge 2 -type structure respectively. h-CeIr 2 Si 2 exhibits a phase transition into a ThCr 2 Si 2 -type low temperature modification ( T u ≈ 920 ° C ). The magnetic behaviour at low temperatures is characterized by the onset of antiferromagnetic ordering in the case of CeRh 2 Si 2 whereas a non-magnetic cerium ground state is proposed for the remaining platinum metal members Ce{Ru, Pd, Os, Ir, Pt} 2 Si 2 , which was interpreted in terms of the interconfiguration fluctuations model. Boron solubility in Ce{Ru, Os} 2 Si 2− x B x at 1000 °C was found to be limited at x ≈ 1 and resulted in a rather small change in the susceptibility values as compared with those of the ternary silicides CeRu 2 Si 2 and CeOs 2 Si 2 .

Ternary compounds REMSb2, RE≡La, Ce, Pr, Nd, Sm, Gd; M≡Mn, Zn, Cd; compound formation, crystal structure and magnetism

Abstract Ternary compounds REMnSb 2 (RE  La, Ce, Pr, Nd, Sm), REZnSb 2 (RE  La, Ce, Pr, Nd, Sm, Gd) and RECdSb 2 (RE  La, Ce, Pr, Nd, Sm) were synthesized. From room temperature X-ray powder diffractometry all compounds were found to crystallize with the ZrCuSi 2 -type structure. The magnetic behavior of REMnSb 2 compounds is characterized by the onset of ferromagnetism of the Mn sublattice in the temperature range between 100 and 520 K. Ordering of the rare-earth sublattice below 50 K is indicated for samples containing Ce, Pr and Nd. CeZnSb 2 remains paramagnetic in the temperature range investigated (4.2–550 K).