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.     

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.     

High temperature superconductivity in rare-earth (R)-barium copper oxides (RBa2)Cu3O9−σ

The series of rare-earth (R)-barium copper oxides with nominal composition (RBa₂)Cu₃O_9−σ and the prototype compound (YBa₂)Cu₃O_9−σ have been prepared from the R (except Pm), Y, and Cu oxides and Ba carbonate by sintering, followed by arc-melting and annealing in pure oxygen. X-ray diffraction measurements show that, except for R = Ce, Tb, and Lu, the compounds have the perovskite-type structure reported by Cava et al. for high superconducting transition temperature T_c (YBa₂)Cu₃O_9−σ. Electrical resistivity and magnetic susceptibility vs temperature measurements reveal super-conductive onsets above 90 K for all R elements, except La, Ce, Pr, and Tb, for which no superconductivity was observed down to 4.2 K. Light (heavy) rare-earth compounds tend to have relatively little (large) orthorhombic splitting in their X-ray patterns, relatively high (low) normal-state resistivities with negative (positive) temperature coefficients, and broad (sharp) superconductive transitions. The negligible destructive effect of the R magnetic moments on superconductivity indicates that the superconducting electrons are primarily associated with the Cu-O polyhedral clusters and interact only weakly with the R ions, suggesting that the (RBa₂)Cu₃O_9−σ compounds may constitute an interesting new class of “high T_c” magnetic superconductors.     

MAGNETIC PROPERTIES OF NEW SERIES R-Mo-Fe NITRIDES WITH THE ThMn12-TYPE STRUCTURE AT A LOWER Mo CONTENT

A systematic study has been made on formation condition, crystallographic structure and magnetic properties of RMo_1.5Fe_10.5N_x, where R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er. The interstitial nitrogen atom effects on Curie temperature, saturation magnetization and magneto-crystalline anisotropy have been investigated. Two important preliminary results have been obtained. (1) A single phase crystallized in the ThMn₁₂-type structure was stabilized with a smaller content of molybdenum, thus, the compounds possess a higher Curie temperature and a larger spontaneous magnetization. (2) A complete system of compounds with 1:12 type structure containing the light rare earth cerium and praseodymium was synthesized, which will be favorable for developing new rare earth hard magnetic materials.     

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.     

Spontaneous magnetostriction in R2Fe14B (R=Y,Nd, Gd,Tb, Er)

Thermal expansion anomalies of R₂Fe₁₄B (R=Y, Nd, Gd, Tb, Er) stoichiometric compounds were studied by X-ray diffraction with high-energy synchrotron radiation using a Debye–Scherrer geometry in temperature range of ∼10–1000 K. A large invar effect with a corresponding large temperature dependence of lattice parameters ∼10–15 K above their Curie temperatures (T_c) are observed. The a-axes show a larger invar effect than the c-axes in all compounds. The spontaneous magnetostrain of the lattices and bonds are calculated. The iron sublattice is shown to dominate the volumetric spontaneous magnetostriction of the compounds and the contribution from the rare-earth sublattice is roughly proportional to the spin magnetic moment of the rare earths. The bond-length changes are consistent with the theoretical spin-density calculation. The average bonds magnetostrain around Fe sites is approximately proportional to their magnetic moments.     

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.     

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：}     

Mössbauer studies of interstitial rare earth-iron intermetallics

Two series of interstitial rare earth-iron intermetallics, R₂Fe₁₇N_3-σ and R₂Fe₁₇C_3-σ have been prepared by gas phase reaction from the R₂Fe₁₇ parent compounds (R=Ce, Pr, Nd, ... Lu and Y). The interstitials raise the Curie temperature of the compounds by 390 K in the case of N and 330 K in the case of C. Mössbauer spectra at 15 K and 293 K, and data as a function of temperature for R=Er and Tm are analysed to yield hyperfine interactions at the four sites, and information on the local magnetization and its orientation. The change in hyperfine field is not proportional to the change in magnetization produced by the interstitials, being much greater in the nitrides than the carbides. Likewise for the isomer shifts. These effects are discussed in terms of the differences in electronic structure of the nitrides and carbides.     

Magnetic studies of RCo12B6 compounds (R=Y,Ce, Pr,Nd, Sm,Gd and Dy)

Magnetization of the RCo₁₂B₆ borides (R=Y, Ce, Pr, Nd, Sm, Gd and Dy), which crystallize in a rhombohedral structure of the SrNi₁₂B₆-type, has been measured in the temperature range 4.2–300 K. All compounds were found to order magnetically with Curie temperatures ranging from 154 to 177 K. Saturation moments at 4.2 K were found to be 6.5, 5.4, 8.4, 8.8, 6.8, 2.1 and 5.9μ_B/f.u. for R=Y, Ce, Pr, Nd, Sm, Gd and Dy, respectively. These results imply a ferromagnetic coupling of Co and rare earth moments for light rare earths and an antiferrimagnetic coupling for heavy rare earths in these compounds. A spin-compensation effect is observed in GdCo₁₂B₆ alloys at T_comp=46 and 72 K, respectively. Results suggest that in CeCo₁₂B₆ the Ce ion exists in the quadripositive state. It is clear that RCo₁₂B₆ materials are not of interest for permanent magnet applications.     

Magnetic properties and structure of hydrogen-amorphized intermetallic compounds RFe2Hx (R=Y, Gd, Tb, Dy, Ho, Er)

The magnetic properties and structure of hydrogen-amorphized RFe₂H_x compounds (R=Y, Gd, Tb, Dy, Ho, Er) have been studied. It is shown that amorphization of the RFe₂H_x hydrides results in an increase of Fe-Fe, and a decrease of R-Fe exchange interaction energy compared to their crystalline hydride counterparts. The magnetic structure of amorphous RFe₂H_x compounds, with the exception of those with R=Y and Gd is apparently noncollinear ferrimagnetic, as in the crystalline hydrides. A model of the heterophase state of amorphous RFe₂H_x hydrides based on x-ray diffraction and magnetic data is proposed. Fiz. Tverd. Tela (St. Petersburg) 39, 908–912 (May 1997)     

RCo10Mo2(R=Y,Ho)化合物的磁性研究

利用SQUID磁强计和脉冲强磁场设备对RCo₁₀Mo₂(R=Y,Ho)化合物的磁性进行了研究.单个晶格模型和双子晶格模型和双子晶格模型被分别用于解释取向样品的磁化过程,稀土次晶格和过渡金属次晶格的各向异性以及它们之间的相互作用由此得到了较好的描述. 关键词：     

Ferrimagnetism and hyperfine interactions in RFe5Al7(R = rare earth)

Magnetization and Mössbauer (⁵⁷Fe, ¹⁵⁵Gd) studies of RFe₅Al₇(R = Y, Sm to Lu, ThMn₁₂ crystal structure) in magnetic fields up to 50 kOe and temperatures 4.1 to 500 K have been performed. The Mössbauer studies yield the distribution of the iron ions among the various inequivalent crystallographic and magnetic sites, the hyperfine fields and their temperature dependence. The magnetization curves display a great variety of unusual magnetic phenomena. Among those; strong anisotropy, magnetic and thermal hysteresis (H_c = 24 kOe for DyFe₅Al₇ at 4.1 K), negative magnetization at low temperatures when the sample is cooled in a magnetic field (even in 1 Oe), compensation points, maxima points and time-dependent magnetization. Most of the phenomena observed can be explained in terms of a spin structure previously suggested for the RFe₆Al₆ compounds, composed of 4 magnetic sublattices. The rare earth moments lie antiparallel to the iron moments in the (j) site and to the ferromagnetic component of a canted antiferromagnetic structure of iron in the (f) site. Iron in the (i) site is nonmagnetic.     

The intersublattice molecular field in the rich Fe−4f intermetallics

Some experimental evidence is given to show that the3d-4f spin coupling parameter is rather insensitive to the kind of the rare earth spin and iron composition in the R _n Fe _m intermetallics. The intersublattice molecular field has been calculated for the rich Fe–4f compounds on the basis of a value of 6.72 K for this parameter as derived from high magnetic field studies. This field affects the R magnetic moment and originates from iron sublattice in the R₂Fe₁₇, R₆Fe₂₃, RFe₃ and RFe₂ compounds. The values of the field for the new magnetic materials of the R₂Fe₁₄B type have also been calculated.     

Nuclear magnetic resonance of RCo3(R:Rare earth)

The nuclear magnetic resonance of⁵⁹Co nuclei in magnetic domains of RCo₃(R:Y, Nd, Sm, Gd, Tb, Dy and Ho) has been measured under external fields up to about 50 kOe at 4.2 K. To assign the observed NMR signals to each Co site, the⁵⁹Co nuclear magnetic resonance of R(Co_1−xNi_x)₃ and R(Co_1−xFe_x)₃ has also been measured under the same conditions. The results of NMR studies show that the cobalt atoms at the 6c site in the light R compounds(YCo₃, NdCo₃ and SmCo₃) and these at the 3b site in the heavy R compounds(GdCo₃, TbCo₃ and HoCo₃) have a large orbital contribution.     

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     

EXAFS study of intermetallics of the type RGe2 (R=La,Ce, Pr,Nd, Sm,Gd, Tb,Dy, Ho,Er and Y) Part I: Determination of Ge-Ge distances

A study of theEXAFS associated with theK x-ray absorption discontinuity of germanium in pure germanium and in the rare-earth germanides RGe₂ (where R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) has been carried out. The Ge-Ge distances have been obtained in these compounds. Considering the phase to the RGe₂ system, the bond lengths in these compounds have been determined. The values obtained by us for the RGe₂ compounds (R=La, Ce, Pr, Nd, Sm, Gd, Dy and Y) agree with those obtained earlier by crystallographic methods. The bond lengths for the compounds TbGe₂, HoGe₂ and ErGe₂ are also being reported.     

Cooling by adiabatic (DE)pressurization - the barocaloric effect

Abstract

The barocaloric effect reflects a new cooling principle at low temperatures without the need of liquefied gases nor magnetic fields as used in other cooling techniques. A pressure induced structural and/or magnetic phase transition is used to obtain a significant change in the system's entropy which leads to its cooling if done adiabatically. The effect is illustrated for the two rare earth compounds Pr₁ ? _xLa_xNio₃ and Ce_x(La,Y)₁ ? _xSb using a structural and a magnetic phase transition, respectively. In situ experiments on Ce_x(La,Y)₁?_xSb are presented and reveal a cooling rate of up to 2 K per 0·5 GPa pressure change at working temperatures below 20 K for x=1 and up to 0·42 K per 0·24 GPa for x=0·85 at around 10K.     

Mössbauer study of magnetic order in RBa2Fe3O8

Complete replacement of copper by iron in RBa₂Cu₃O₇ leads to RBa₂Fe₃O₈ (R=Y, rare earth). Mössbauer spectroscopy measurements of⁵⁷Fe and¹⁵¹Eu in RBa₂Fe₃O₈ (R=Y, Eu, Ho, Er) at temperatures 4.2–800 K have been performed. Some of the spectra reveal two inequivalent iron sites, probably corresponding to iron in the Fe(2) site (fivefold oxygen coordination) and in the Fe(1) site (octahedral oxygen coordination). In all compounds the iron moments order antiferromagnetically at the same Néel temperatureT _N720 K. The¹⁵¹Eu Mössbauer spectra of EuBa₂Fe₃O₈ show that the Eu ion is trivalent and exposed to a small exchange field from the iron sublattices.     

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：}