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

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 < T < 1100 K and in fields up to 1.3 T revealing a typical Van Vleck paramagnetism of free RE³⁺-ions for temperatures T > 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 (μ_eff = 0.7 BM) compare well with the ideal Van Vleck behavior of Sm₃₊ ions with a $\text{J =}\text{5}\text{2}$ ground state and a low-lying excited first level $\text{J =}\text{7}\text{2}$. 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 properties and structural chemistry of ternary silicides (RE,Th, U)Ru2Si2 (RE = RARE EARTH)

Ternary silicides (RE, Th, U)Ru₂Si₂ 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 ThCr₂Si₂ (ordered derivative of the BaAl₄-type). The magnetic behavior of these alloys was studied in the temperature range 1.5 K < T < 1100 K. Magnetic susceptibilities at temperatures T > 300 K closely follow a typical Van Vleck paramagnetism of free RE³⁺-ions. In the case of CeRu₂Si₂ susceptibilities are well described for 20 K < T < 1100 K by a Van Vleck paramagnetism of widely spaced multiplets; the observed effective paramagnetic moment μ_eff = 2.12 BM indicates a high percentage (85%) of Ce³⁺. SmRu₂Si₂ yields an effective moment μ_eff = 0.54 BM, which compares reasonably well with the Hund's 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 Sm³⁺. At low temperatures ferromagnetic ordering was encountered for (Pr, Nd, Ho, Er, Tm)Ru₂Si₂, whereas antiferromagnetic ordering was observed for (Sm, Gd, Tb, Dy)Ru₂Si₂. The ordering temperatures are generally below 55 K. No superconductivity was found for temperatures as low as 1.8 K.     

Magnetic properties of RE2Au compounds (RE = Pr,Nd, Gd,Tb, Dy,Ho, Er,Tm and Y)

Magnetic properties of nine RE₂Au compounds have been studied in fields of up to 19 kOe in the temperature range 4.2K–300K. It has been found that all compounds are paramagnetic at room temperature except Gd₂Au. The compounds with Pr, Nd, Ho, Er and Tm exhibit Curie-Weiss behaviour with paramagnetic moments in close agreement with those expected for the free RE³⁺ ion. The moment of gold was found to be zero. The compounds with Pr, Nd, Tb, Dy, Er and Tm are antiferromagnetic at low temperatures. It appears that Ho₂Au is ferromagnetically ordered below 4.5 K. No evidence for magnetic ordering was found for Y₂Au. The compound with Tb exhibits metamagnetic behaviour.     

Magnetic properties of RCoSi2 compounds (R=rare earth)

New ternary silicides of composition RCoSi₂ (R=rare earth and Y) have been prepared and found to crystallize in the orthorhombic CeNiSi₂-type structure. Their magnetic properties have been studied by means of susceptibility measurements between 2 and 250 K. The Ce and Y compounds show essentially temperature independent Pauli paramagnetism. The compounds with R=Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm show antiferromagnetic ordering below 20 K. The effective rare earh moments in the paramagnetic state agree well with the free ion values, and, for the heavy rare earths, the Néel temperatures vary with the De Gennes factor. There is no indication for a magnetic contribution from the Co sublattice.     

Magnetic properties of R2Pt compounds with R = Gd,Tb, Dy,Ho, Er and Tm

Magnetic properties of polycrystalline samples of R₂Pt compounds (R = Gd, Tb, Dy, Ho, Er and Tm) are presented. The Gd, Td, Dy, Ho based compounds are ferromagnetic with Curie temperatures ranging between 155 and 17 K. Er₂Pt and Tm₂Pt are antiferromagnetic with Néel temperatures of 9 and 5 K respectively. The observed properties are discussed considering indirect exchange interactions and crystal field effects acting on the rare earth ions which lies in very low symmetry sites.     

Magnetic properties of ternary gallides of type RNi4Ga (R=rare earths)

The magnetic properties of RNi₄Ga (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) compounds have been investigated. These compounds form in a hexagonal CaCu₅ type structure with a space group P6/mmm. Compounds with the magnetic rare earths, R= Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm, undergo a ferromagnetic transition at 5, 17, 20, 19, 12, 3.5, 8 and 6.5 K, respectively. The transition temperatures are smaller compared to their respective parent compounds RNi₅. PrNi₄Ga is paramagnetic down to 2 K. LaNi₄Ga and LuNi₄Ga are Pauli paramagnets. All the compounds show thermomagnetic irreversibility in the magnetically ordered state except GdNi₄Ga.     

Magnetic and structural studies of the alloy system REIn0.5Ag0.5

The structural and magnetic properties of the alloy system REIn_0.5Ag_0.5 [RE = Gd, Tb, Dy, Ho, Er, Tm and Yb] are reported. All these alloys (except that of Yb) crystallize in a cubic CsCl type structure at room temperature. Low temperature X-ray diffraction data does not reveal any structural phase transformation down to 8 K. On the basis of magnetic susceptibility data at a different temperature (3–300 K) and applied magnetic field (2 × 10⁵ to 8 × 10⁶ A m^-1, it has been concluded that GdIn_0.5Ag_0.5 is ferromagnetic (T_c = 118 K), TbIn_0.5Ag_0.5 and DyIn_0.5Ag_0.5 are meta magnetic (T_N = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (T_N) equal to 24, 22, 21 and 20 K, respectively. The evaluated effective magneton number (p) is found to be slightly larger compared to theoretical values for tripositive ions of Gd, Tb and Dy and a bit smaller for Ho, Er, Tm and Yb. The results have been qualitatively explained using appropriate theories.     

Susceptibility measurements on some R5In3 compounds

The magnetic susceptibility of some rare earth-indium compounds has been measured in the temperature range 4.2–300 K under a constant field of 1 kOe. The compounds with R = Gd, Tb and Dy are antiferromagnetic, having Néel temperatures between 4.2 and 78 K ; those with R = Ho, Er and Tm seem to be ferromagnetic with ordering temperatures probably below 4.2 K. Y₅In₃ presents a temperature independent susceptibility.     

Magnetic properties of the rare-earth diborodicarbides (RB2C2)

The magnetic susceptibility of RB₂C₂ has been measured in the temperature range of 3–300 K. Curie-Weiss fits to the susceptibilities led to effective moments in agreement with those expected for R³⁺ ions. The RB₂C₂ (R = Ce, Nd, Sm, Gd, Tb, Er, and Tm) compounds are antiferromagnetic. Metamagnetic transitions at low fields were observed for CeB₂C₂ and TbB₂C₂. The compounds, DyB₂C₂ and HoB₂C₂, are ferromagnets with complex magnetic structures. Praseodymium borocarbide becomes a Van Vleck paramagnet at low temperature. The magnetic ordering temperatures of these compounds are discussed in terms of their crystal structure and the RKKY theory.     

Susceptibilite magnetique des composes ternaires TCu2Ge2(T = Gd,Tb,Dy,Ho,Er,Tm)

Susceptibility measurements are performed on the tetragonal TCu₂Ge₂ ternary compounds in the temperature range 4.2–200 K under a constant magnetic field of 5 KOe. The compounds with T = Gd,Tb,Dy and Ho are antiferromagnetic with Néel temperatures 12,15,8 and 6.4 K respectively. The compounds with T=Er and Tm do not show any ordering temperature down to 4.2 K. The temperature dependence of the reciprocal susceptibility of all compounds follows a Curie-Weiss law. The paramagnetic Curie temperatures for all compounds are negative.     

A new family of rare earth compounds,the ternary silicides RE2RhSi3 (RE = Y,La, Ce,Nd, Sm,Gd, Tb,Dy, Ho,Er) - crystal structure electrical and magnetic properties

New ternary silicides RE₂RhSi₃ (RE = Y, La, Ce, Nd, Sm, Gd, Tb, Dy, Ho, Er) have been prepared. They crystallize with a hexagonal symmetry structure which is derived from the AlB₂-type. Si and Rh atoms are inside RE₆ distorted trigonal prisms and are ordered in a two dimensional sublattice perpendicular to the c axis. The a and c parameters are approximately twice those of the corresponding disilicides RESi₂. La₂RhSi₃ and Y₂RhSi₃ are not superconducting down to 1.6 K. Nd₂RhSi₃ is ferromagnetic at 15 K, but the other silicides order antiferromagnetically with metamagnetic phase transitions for certain of them.     

Magnetic properties of some RPd2Si2 compounds (R=Gd,Tb, Dy,Ho and Er)

The magnetic susceptibility of the ternary compounds, RPd₂Si₂ (where R=Gd, Tb, Dy, Ho and Er) has been measured. GdPd₂Si₂ order antiferromagnetically at 13 and 20 K respectively; the rest of the compounds do not show clear ordering down to 4.2 K. Palladium carries no moment in these compounds. The De Gennes formula is not obeyed indicating that the exchange interaction between the 4f moments via conduction electrons is not isotropic     

Structural relative stabilities and pressure-induced phase transitions for lanthanide trihydrides REH3 (RE=Sm,Gd, Tb,Dy, Ho,Er, Tm,and Lu)

The structures, structural relative stabilities, pressure-induced phase transitions, and equations of state for lanthanide trihydrides REH₃ (RE=Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) are systematically studied using ab initio calculations under a core state model (CSM). The obtained ground-state parameters, such as lattice constants and bulk modulus, agree well with the available data. Among the P6₃/mm, P3?c1, and P6₃cm structures, the P6₃cm structure is found to be the most stable structure for lanthanide trihydride via the comparison of the calculated total energies. With the help of Birch–Murnaghan equation of state, the structural transitions from hexagonal to cubic for REH₃ (RE=Sm, Gd, Ho, Er, and Lu) under pressure are affirmed; especially, the similar behavior of REH₃ (RE= Tb, Dy, and Tm) is reasonably predicted for the first time by this means. For the transitions, the repulsive interactions of H–H atoms may play an important role in terms of the analysis of the structures in the vicinity of the theoretical phase transition.     

Magnetic properties of RNi2Si2 compounds (R= rre earth)

We report an extensive study of the magnetic properties of tetragonal RNi₂Si₂ compounds (R=Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm), through resistivity, neutron diffraction, susceptibility and magnetization experiments. All compounds exhibit complex incommensurate antiferromagnetic structures, while a transition occurs in TbNi₂Si₂ between a modulated phase and a simple antiferromagnetic structure, stable at low temperature. The magnitude of the bilinear exchange interactions deviates from the Gennes law and the direction of the ordered magnetic moments presents anomalies across the series, including the probable existence of other types of interactions between the rare earth ions.     

Magnetic properties of RAu2Si2 rare earth compounds

The magnetic properties of the R Au₂Si₂ compounds with R = Ce-Er have been investigated. It was found that the compounds for which R = Ce, Sm, Gd, Tb and Dy are antiferromagnetically ordered at temperatures ranging from 5.7 to 15.9°K. PrAu₂Si₂ and NdAu₂Si₂ exhibit paramagnetic behavior for temperatures as low as 4.2°K. The magnetic structure is ferrimagnetic for the compounds in which R = Eu, Ho, and Er. The Eu compound is in the divalent state. The Néel and Curie points for this system do not follow the De-Gemnes function. Curie-Weiss Behavior is exhibited by all the compounds with effective moments in good agreement with that of a free tripositive lanthanide ion. The difference in magnetic properties between R Au₂Si₂ and the isomorphous R Fe₂Si₂ series is discussed.     

The magnetic hyperfine field at Cd nuclei in the rare earth ferromagnets Gd,Tb, Dy,Ho, Er and Tm

The time differential perturbed angular correlation technique has been used to study the combined magnetic and electric hyperfine interactions at the site of a¹¹¹Cd impurity in the rare earth ferromagnets Gd, Tb, Dy, Ho, Er, and Tm at 4.2 °K. The following magnetic hyperfine fields at the site of¹¹¹Cd have been found: ¦H _hf ¦=340(7) kG in Gd, 275 (5) kG in Tb, 221 (4) kG in Dy, 116 (3) kG in Er and 60 (6) kG in Tm. In Ho two magnetically different sites were observed with magnetic fields of 159 (3) and 139 (3) kG. Both sites are equally populated. The coupling constantJ _5f of the conduction electron-4f interaction has been calculated for the different rare earth metals from the measured hyperfine fields by means of the RKKY theory.     

The Magnetic Hyperfine Field of 111Cd in the Rare Earth–Nickel Laves Phases RNi2

The magnetic hyperfine field of ¹¹¹Cd in the C15 Laves phases RNi₂ has been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature for the rare earth constituents R = Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm.     

Low temperature magnetization measurements on heavy rare earth molybdenum sulfides, (RE)1.2Mo6S8

Magnetization measurements on the heavy rare earth molybdenum sulfides, (RE)_1.2Mo₆S₈ (RE = Gd, Tb, Dy and Ho) were performed to further clarify the natures of their magnetic orders found in our recent resistivity and ac susceptibility measurements below 1 K. The variations of their magnetic and superconducting transition temperatures along the series of the rare earth ions in the Periodic Table are interpreted by means of available theories.     

Magnetic susceptibility and electrical resistivity of some Th2Zn17-type rare-earth zinc phases

We report measurements of the magnetic susceptibility and electrical resistivity of the iostructural compounds RE₂Zn₁₇ (RE=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu). The composition dependence of the lattice parameter and effective moment indicate that all the RE ions are trivalent except Yb which is divalent. Magnetic order is observed in compounds where RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er. A second transition is seen for RE=Pr, Ho, Sm and Tb. Superzone boundary effects are observed in the electrical resistivity of these four alloys as well as in Er₂Zn₁₇. Resistivity measurements reveal concentrated Kondo behavior (or 4f instability) of Ce in Ce₂Zn₁₇.     

Magnetic properties of ternary rare-earth compounds of the type R2Fe14B

Ternary tetragonal compounds of the composition R₂Fe₁₄B were observed for R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The lattice constants and the X-ray density of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 20 T. These latter measurements were made in two mutually perpendicular directions, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy was found to consist of contributions due to the Fe and rare-earth sublattice, respectively.