Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Anomalous hyperfine field and orbital moment of cobalt in RCo2; R = Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Tm

⁵⁹Co spin echo NMR spectra in the magnetically ordered phase of the MgCu₂ type RCo₂ compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been observed. For the RCo₂ with the easy direction of magnetication parallel to the 〈011〉 or 〈111〉 direction, the ⁵⁹Co hyperfine fields at two magnetically inequivalent Co sites are found to be antiparallel, revealing a large anisotropy in the ⁵⁹Co hyperfine field. The results are discussed in terms of a large and anisotropic orbital moment of Co. The transferred hyperfine field due to rare earth spins is estimated from well resolved satellite lines observed in Tb_1?xY_xCo₂. The nuclear quadrupole splitting in the magnetically ordered phase is found to be always larger than that in the paramagnetic phase.     

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.     

Tetragonal distortion from cubic symmetry at lower temperatures in the Cs2NaLnCl6 compounds (elpasolites) with light lanthanides

Single crystal magnetization- and NMR-measurements show that the Cs₂NaLnCl₆ compounds with the light rare earth Ce and Nd, contrary to that with the heavy rare earth Ho, are tetragonally distorted from cubic symmetry at lower temperatures. Because of this distortion, detailed single crystal magnetization data are required in order to evaluate the Ln crystal-field level scheme. The size of the distortion is such that it splits the ground quadruplet of Nd⁺³ into doublets nearly two Kelvin apart.     

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 Mössbauer studies of FeNb2O6

Fe⁵⁷ Mössbauer spectra of FeNb₂O₆ were obtained from 15.0K down to 1.9 K. The isomer shift, 1.42±0.01 mm sec^?1 relative to Cr, was found to be temperature independent, whereas the magnitude of the quadrupole splitting was observed to decrease slightly with temperature. The quadrupole splitting and the hyperfine field at 1.9 K are -2.41±0.01 mm sec^?1 and 34.6±0.3 kOe respectively. The directions of the hyperfine fields experienced by the Fe nuclei are in the a-c plane symmetrically displaced with respect to the crystallographic axes.     

Rare earth single-ion anisotropy and the magnetic structures of the RTiO3 perovskites: R = Tb,Dy, Ho,Er and Tm

Attention is drawn to common features in the magnetic structures of the isostructural RMO₃ phases where R = Tb, Dy, Ho, Er and Tm and M = Al, Ti, Cr, Fe and Co. The orientation of the rare earth magnetic moment with respect to the orthorhombic c-axis depends only on R. For R = Er and Tm the moments are parallel to the c-axis while for R = Tb, Dy and Ho they lie in the a-b plane. The in-plane moments are canted with respect to the a and b axes with both ferromagnetic and antiferromagnetic components and the canting angles are constant for a given R independent of M. Using symmetry arguments we show that the above systematics can be understood in terms of the rare earth single-ion anisotropy. Detailed calculations incorporating a crystal field of C_s symmetry determined for Er³⁺ in YAlO₃ and an isotropic molecular field of magnitude appropriate to the RTiO₃ compounds produce results in agreement with the experimental observations. Essentially the same results are obtained for a crystal field of D_4h symmetry. The B²₀O²₀ term in the crystal field Hamiltonian is identified as the factor which determines the orientation of the rare earth moment.     

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.     

Sn Mössbauer spectroscopy of Gd0.8L0.2Mn6Sn6 and Tb0.8L0.2Mn6Sn6 compounds (L=Sc,Y, Lu)

The HfFe₆Ge₆-type compounds Gd_0.8L_0.2Mn₆Sn₆ and Tb_0.8L_0.2Mn₆Sn₆ (L = Sc, Y, Lu) have been studied by ¹¹⁹Sn Mössbauer spectroscopy. The values of the apparent quadrupolar splitting clearly evidence the easy plane magnetization of the gadolinium compounds and the easy axis one in the terbium compounds. The three tin sites behave differently with the nature and size of the substituting L element. For a given series, the hyperfine field of the Sn_2d site is almost unchanged whatever the size of the L element. The hyperfine field of the Sn_2e site strongly varies with the L size in relation with atomic displacements. The hyperfine field of the Sn_2c site exhibits a more complicated behavior. The field difference in the easy plane and easy axis compounds confirms the angle-dependent anisotropic contribution of the Mn moment to the hyperfine field. The analysis of the results also suggests the play of angle-dependent contributions arising from the rare earth moment.     

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 R3Rh2 compounds with R=Gd, Tb,Dy, Ho and Er

Bulk magnetic measurements performed on polycrystalline samples of the tetragonal compounds R₃Rh₂ with R=Gd, Tb, Dy, Ho and Er are presented. All the compounds are ferromagnetic at low temperature. However in Tb₃Rh₂ an antiferromagnetic behaviour is observed between 14 and 24 K. In Gd₃Rh₂, where the magnetocrystalline anisotropy must be negligible, it seems that the magnetic structure is not collinear. In the other compounds the observed properties essentially result from indirect exchange interactions and crystal field effects acting on the rare earth ions which lie in low symmetry sites.     

Power factors of late rare earth-doped Ca3Co2O6 oxides

Polycrystalline samples of (Ca_1−xR_x)₃Co₂O₆ with R = Gd, Tb, Dy and Ho at x=0-0.1 were synthesized and the effects of rare earth substitution on their thermoelectric properties were investigated. In the high-temperature region, the rare earth substitution resulted in an increase in the Seebeck coefficients (S), and the S values increased with decreasing ionic radius of rare earth elements in the order Gd³⁺>Tb³⁺>Dy³⁺>Ho³⁺. In contrast, the influence of rare earth substitution on the electrical resistivity was small. The high-temperature power factor was thereby improved by the late rare earth substitutions, particularly those with Ho³⁺ for Ca²⁺. For the Ho-doped samples (x≤0.05), the power factor was significantly improved by increasing Ho concentration.     

Properties magnetiques des composes terres rares-plomb TPb3(T = Pr,Nd, Sm,Tb, Dy,Ho)

We have studied the low field susceptibility of TPb₃ compounds (T = Pr, Nd, Sm, Tb, Dy, Ho) between 3 and 300 K. All these compounds except SmPb₃ follow a Curie-Weiss law with a paramagnetic moment close to the free ion value. The compounds with Sm, Tb, Dy and Ho order antiferromagnetically.The magnetization of the three last compounds has been studied in static magnetic fields up to 85 koe.     

Exchange-striction of rare earth-Al2 laves phase compounds

The exchange-striction of the cubic Laves phase compounds R-Al₂ (R =Gd, Tb, Dy, and Ho) has been determined at 0 K from measurements of thermal expansion. The results are interpreted in terms of rare earth sublattice (R-R) interactions, using the molecular field approximation. It is found that the signs of the strain derivatives of the molecular field constants are positive for Dy-Al₂ and Ho-Al₂ and negative for Gd-Al₂ and Tb-Al₂ compounds.     

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.     

Rfe10.5V1.5Nx化合物的结构和内禀磁性研究

系统地研究了Rfe_10.5V_1.5N_x（Ｒ＝Ｙ，Ｃｅ，Ｎｄ，Ｓｍ，Ｇｄ，Ｔｂ，Ｄｙ，Ｈｏ，Ｅｒ）化合物的结构和内禀磁性，并与相应的Rfe_10.5V_1.5N_x化合物进行了比较。同Rfe_10.5V_1.5N_x化会物相比，由于ｖ含量低，Rfe_10.5V_1.5N_{x关键词：}     

Transferred hyperfine fields at 119Sn in Fe1−xMxSn [M≡Mn, Co and Ni]

The transferred hyperfine fields at ¹¹⁹Sn, using Mössbauer spectroscopy are reported for the hexagonal B-35 compounds with a general formula Fe_1?xM_xSn, where MMn, Co and Ni. In these compounds, Sn atoms occupy two crystallographically inequivalent sites. For FeSn the observed spectrum consists of a quadrupole doublet and a magnetic pattern corresponding to 2(d) and 2(a) sites respectively. The data have been analysed to resolve the controversy regarding hyperfine parameters. On replacing Fe by Mn atoms, additional lines appear in the higher velocity region of the Mössbauer spectrum and the intensity of the nuclear Zeeman pattern increases at the expense of quadrupole doublet. The resulting Mössbauer spectra have been analysed by taking only the nearest neighbour interactions into account. This analysis shows that on replacing each Fe atom by a Mn atom, the hyperfine field at 1(a) Sn site increases by about 40 kOe and a field of about 35 kOe is produced at the 2(d) Sn sites. Further, from the nuclear Zeeman pattern for 2(d) sites, the sign of quadropole splitting for these sites could also be determined and was found to be positive. However, the substitution of Co and Ni in place of Fe atoms results in a broad unresolved pattern suggesting that the hyperfine field at the 1(a) sites decreases and a finite field develops at the 2(d) site. The origin of transferred hyperfine fields at the two inequivalent Sn sites is discussed, the magnetic transition temperatures of these compounds have been estimated and the magnetic moments of M-atoms have been inferred.     

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.     

NMR of 27 Al in paramagnetic single-crystal DyAl2

NMR of ²⁷Al was observed in a spherical single crystal of DyAl₂ in the paramagnetic state. The well split quadrupole spectrum yielded a quadrupole frequency ν_Q = 561 kHz and hyperfine constant H_hf^p = -3.17 kOe/n_B. The anisotropy of the spectrum is well explained by the dipolar interaction.     

Magnetic anomalies of thermal expansion in (rare-earth) Ni2 intermetallic compounds

The thermal expansion of eight RENi₂ intermetallic compounds (RE = La, Nd, Sm, Tb, Dy, Ho, Er, Tm) and YNi₂ have been measured between 3.8 and approx. 300 K. The anomalies found at the paramagnetic-magnetically ordered phase transition have allowed an accurate determination of the Curie temperatures. From the low temperature comparison of the thermal expansion of the light RE compounds with that of LaNi₂, and of the heavy RE compounds with that of YNi₂, the Debye temperatures have been obtained. In the case of the compounds DyNi₂, TbNi₂ and HoNi₂ the contributions from crystal field and exchange interactions to the spontaneous volume strain at the magnetically ordered phase have been calculated, the agreement between experiment and calculation being good.