Magnetic properties of ternary RMn2Si2 and RMn2Ge2 compounds

Magnetic properties of RMn₂Si₂ and RMn₂Ge₂ compounds, where R is a rare earth metal, have been investigated by magnetometric measurements. RMn₂Ge₂ (where R is a light rare earth) and LaMn₂Si₂ are ferromagnets. Remaining compounds have antiferromagnetic properties. DyMn₂Si₂ and ErMn₂Si₂ show ferromagnetic properties at low temperatures. It was confirmed that the value of Curie (or Néel) temperature for the Mn sublattice decreases with increasing c constant.     

Magnetic ordering in rare earth iron silicides and germanides of the RFe2X2 type

Rare earth iron silicides and germanides of the RFe₂Si₂ or RFe₂Ge₂ type with R = La, Ce, Pr, Nd, Sm, Gd and Dy were measured for their magnetic susceptibility. The silicides and germanides of Nd and Gd are antiferromagnetically ordered below a Neel point of, respectively, 11 and 7°K for the silicides and 13 and 11 for the germanides. The Nd sublattice under-goes a spin-flop transition which at 4.2°K is at 11 KOe. Although the Fe sublattice is diamagnetic, all the samples showed a weak ferromagnetic ordering below a temperature of about 700°K. The ratio between the dia- and ferromagnetic phases is 94:6 per cent in the silicides and 80:20 in the germanides, as determined by Mössbauer spectroscopy and supported by magnetization measurements.     

Crystals and magnetic structure of RMn2Si2 (R = Pr, Nd, Y) and YMn2Ge2

Crystallographic and magnetic properties of PrMn₂Si₂, NdMn₂Si₂, YMn₂Si₂ and YMn₂Ge₂ intermetallics were studied by X-ray, neutron diffraction and magnetometric measurements. The crystal structure of all four compounds was confirmed to be body-centered tetragonal (space group I4/mmm). All were found to be antiferromagnetic with Néel points at 368, 380, 460 and 395 K respectively. Neutron diffraction results indicate that their magnetic structure consists of ferromagnetic layers composed of Mn ions piled up along the c-axis. Each layer is antiferromagnetically coupled to adjacent layer. The magnetic space group is I_p4/m′m′m′. No magnetic ordering of the R sublattice was observed at 1.8 K in the case of R = Pr and Nd.     

Magnetic properties of R3Co29Si4B10 (R=La, Ce, Pr, Nd, Sm, Gd and Dy) borides

The crystal structure and magnetic properties of quaternary rare-earth intermetallic borides R₃Co₂₉Si₄B₁₀ with R=La, Ce, Pr, Nd, Sm, Gd and Dy have been studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in a tetragonal crystal structure with the space group P4/nmm. Compounds with R=La, Ce, Pr, Nd and Sm are ferromagnets, while ferrimagnetic behavior is observed for R=Gd and Dy. The Curie temperatures vary between 149 K and 210 K. The Curie temperatures in R₃Co₂₉Si₄B₁₀ (R=Ce, Pr, Nd, Sm, Gd, Dy) compounds are roughly proportional to the de Gennes factors.     

Itinerant and local magnetism,superconductivity and mixed valency phenomena in RM2Si2, (R = rare earth,M = Rh,Ru)°

X-Ray, magnetization and Mossbauer (¹⁵¹Eu, ¹⁵⁵Gd, ¹⁶¹Dy and dilute ⁵⁷Fe) studies of RM₂Si₂ reveal that when R is a magnetic ion the compounds order antiferromagnetically. For M = Rh a second antiferromagnetic phase transition is observed, corresponding to Rh itinerant electron magnetic ordering. In EuRh₂Si₂ the Eu ion is predominantly divalent with a mixed valent component. In EuRu₂Si₂ the Eu is predominantly trivalent. LaRu₂Si₂ and LuRu₂Si₂ display enhanced electron paramagnetism and become superconducting at 3.5 K and 2.4 K respectively. LaRh₂Si₂, YRh₂Si₂ and LuRh₂Si₂ display an itinerant electron magnetic phase transition, T_M (LaRh₂Si₂) = 7 K, and at lower temperatures a superconducting phase transition, T_c(LaRh₂Si₂) = 3.8 K. There is evidence that in the superconducting phase the itinerant magnetic order survives.     

Magnetic ordering in NdRh2Si2 and ErRH2Si2

Neutron diffraction and magnetization study of polycrystalline NdRh₂Si₂ and ErRh₂Si₂ was performed in the temperature range from 4.2 to 293 K. Both compounds are of ThCr₂Si₂ type crystal structure and exhibit antiferromagnetic ordering below T_N = 53 K and T_N = 12.8 K respectively. The magnetic structure wave vector is τ = [0, 0, 1].     

Magnetic and structural characteristics of the RInCu2 compounds in the Heusler L21 structure

Magnetic and structural behaviour of materials of composition RInCu₂ (R = rare earth) were investigated. All the compounds (R = La-Lu) were found to be isotypic and to crystallize with the Heusler L2₁ type structure. The magnetic behaviour of the compounds was studied in the temperature range 2–300 K. The RInCu₂ (R = Sm, Gd, Tb, Dy) compounds are antiferromagnetically ordered at low temperatures T_N = 12 K for GdInCu₂, Ce in CeInCu₂ is in a pure trivalent state. LaInCu₂ is Pauli paramagnetic and LuInCu₂ is diamagnetic. No superconductivity was observed for temperatures as low as 1.8 K. The observed magnetic properties result from indirect exchange interaction and crystal field effects and compared to the isomorphous MnInCu₂.     

Neutron diffraction studies of the magnetic ordering in the rare earth compounds TbNi2Si2, HoCo2Si2 and TbCo2Si2

Neutron diffraction studies and magnetic measurements on the compounds TbNi₂Si₂ (1), HoCo₂Si₂ (2) and TbCo₂Si₂ (3) revealed a collinear antiferromagnetic order below T_N = 10 ± 1 K (1), T_N = 13 ± 1 K (2) and T_N = 30 ± 2 K (3) with the rare earths moments oriented along the c-axis [m₀ = 8.8 ± 0.2 μ_B (1), m₀ = 8.1 ± 0.2 μ_B (2), m₀ = 8.8 ± 0.2 μ_B (3)] and the corresponding wavevector are $\text{k}\text{= [}\text{1}\text{2}\text{1}\text{2}\text{0] (1)}\text{and}\text{k}\text{= [ 0 0 1] (2) (3)}$. The magnetic structure of the compounds HoCo₂Si₂ and TbCo₂Si₂ consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically (+?+?) while for TbNi₂Si₂ the ordering within (0 0 1) plane is antiferromagnetic and the planes (0 0 1) are indeed decoupled.     

Ferromagnetic rare-earth and diamagnetic iron sublattices in ternary RFe0.67Ge1.33 type compounds

The magnetic properties of RM_2?xSi_x and RM_2?xGe_x where R = La, Ce, Nd, Sm, Eu and Gd and M = Fe, Co, Ni and Ag have been measured. It has been found that for samples of x = 0.4 both R and M sublattices are paramagnetically above 4.2δ K in the high spin state, whereas, if x = 0.67, R is magnetically ordered whereas M is diamagnetic.     

Neutron diffraction study of magnetic ordering in PrCu2Si2, PrCu2Ge2, PrFe2Ge2 and NdFe2Ge2

A neutron diffraction study of polycrystalline PrCu₂Si₂ [1], PrCu₂Ge₂ [2], PrFe₂Ge₂ [3] and NdFe₂Ge₂ [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below T_N = 19 ± 1 K [1], T_N = 16 ± 1 K [2], T_N = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu₂Si₂ and PrCu₂Ge₂ and +--+ for PrFe₂Ge₂ and NdFe₂Ge₂. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field.     

Magnetic properties of R2Re2Si2C (R=Ho and Er)

We have investigated magnetic properties of R₂Re₂Si₂C (R=Ho and Er) using magnetic susceptibility, magnetization and heat capacity measurements. Both the materials order antiferromagnetically. The ordering temperatures (T_N) for Ho₂Re₂Si₂C and Er₂Re₂Si₂C are, ∼8.8 and ∼7.6 K, respectively. Our measurements indicate crystal field effects in the bulk properties of both these compounds. The experimental results have been analyzed by taking into account the effect of crystalline electric field and magnetic exchange interaction.     

Neutron diffraction study of magnetic ordering in Tm0.5Eu0.5Se

A single crystal of the magnetic semiconductor Tm_0.5Eu_0.5Se was studied by means of neutron diffraction in the temperature range from 1.8 to 293 K. Long-range magnetic order is detected at temperatures below T_c = (18.5±1) K. The measured ferromagnetic moment component of (2.12±0.05) μ_B per rare-earth ion at saturation in zero external magnetic field indicates approximately antiparallel alignment of Tm moment and Eu spin (mutual angle 134°). The experimentally determined neutron magnetic form factor confirms the divalent state of both Tm and Eu in Tm_0.5Eu_0.5Se.     

The antiferromagnetic structure of ErCo2Si2 by neutron diffraction

The magnetic structure of the tetragonal ErCo₂Si₂ compound is determined by neutron diffraction on powder sample at 4.2 K. The magnetic ordering is connected with a symmetry lowering, magnetic space group P_2s$\text{1}$ (Sh⁷₂)k = 000. The structure is collinear antiferromagnetic with the erbium magnetic moments making an angle of 56.2° with the c axis. The magnetic moment value for erbium is 6.75μ_B.     

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.     

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.     

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.     

First order magnetic phase transition in tetragonal NpCu2Si2

Magnetization and Np²³⁷ Mössbauer studies of the tetragonal compounds NpM₂Si₂ (M = Cr, Mn, Fe, Co, Ni, Cu) were performed. NpMn₂Si₂ is ferromagnetic. All other compounds order antiferromagnetically. Only in NpCu₂Si₂ the Mössbauer studies reveal a first order magnetic phase transition at T_N = 34 K. It is interpreted in terms of Blume's model, originally developed for cubic UO₂.     

Magnetic structures of PrCO2Si2 and TbCo2Si2 compounds

Neutron diffraction studies of polycrystalline PrCo₂Si₂ and TbCo₂Si₂ compounds were carried out at 4.2 and 293 K. Both samples have collinear antiferromagnetic order below T_N(31(1) and 46(1) K for Pr and Tb compound respectively), with their magnetic moments parallel to the c axis. The ordered magnetic moment values of Pr and Tb at 4.2 K (3.19 and 9.12 μ_B respectively), are close to the saturation value of the free ions. The corresponding magnetic space group P_l4/mnc (Sh⁴¹⁰₁₂₈) is body-anticentered ($\text{k =}\text{111}\text{222}$ refering to P_l cell).     

Influence of Si and Co substitutions on magnetoelastic properties of R2Fe17 (R=Y, Er and Tm) intermetallic compounds

The magnetostriction of the off-stoichiometric R₂Fe₁₇-type intermetallic compounds based on R₂Fe_14−xCo_xSi₂ (R=Y, Er, Tm and x=0, 4) was measured, using the strain gauge method in the temperature range 77-460 K under applied magnetic fields up to 1.5 T. All compounds show sign change and reduction in magnetostriction values compared to the R₂Fe₁₇ compounds by Si substitution. For Y₂Fe₁₄Si₂ and Er₂Fe₁₄Si₂, saturation behaviour is observed near magnetic ordering temperature (T_C), whereas for Tm₂Fe₁₄Si₂, saturation starts from T>143 K. Also, Co substitution has different effects on the magnetostriction of R₂Fe₁₄Si₂ compounds. In Er₂Fe₁₀Co₄Si₂ and Tm₂Fe₁₀Co₄Si₂, saturation occurs below the spin reorientation temperature (T_SR). In addition, in Er₂Fe₁₄Si₂, a sign change occurs in the anisotropic magnetostriction (Δλ) as well as the volume magnetostriction (ΔV/V) at their T_SR values. The volume magnetostrictions of the Tm-containing compounds show an anomaly around their T_SR. In R₂Fe₁₄Si₂ compounds, parastrictive behaviour is also observed in ΔV/V near their T_C values. In addition, the magnetostriction of the sublattices is investigated. Results show that in R₂Fe₁₄Si₂ compounds, the rare-earth sublattice contribution to magnetostriction is negative and comparable to the iron sublattice, whereas, in R₂Fe₁₀Co₄Si₂ compounds, the rare-earth sublattice contribution is positive and larger than Fe sublattice. These results are discussed based on the effect of Si and Co substitutions on the anisotropy field of these compounds. Influence of the spin reorientation transition on the magnetostriction of these compounds is discussed in terms of the anisotropic sublattice interactions.     

R2Fe17C化合物的结构与内禀磁性的研究

本文系统研究了R₂Fe₁₇C(R=Y.Sm,Gd,Tb.Dy,Er)化合物的结构与内禀磁性,并与相应的R₂Fe₁₇化合物进行了比较。R₂Fe₁₇C的居里温度比相应R₂Fe₁₇的居里温度增加大约200K。本文讨论了C原子对该化合物结构与磁性的影响,同时,还对Sm₂(Fe_1-xCo_{x 关键词：}