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1.
《Physics letters. A》1988,129(1):67-70
The temperature dependence of the resistivity for quickly quenched LnBa2Cux ceramics, with with Ln=Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb, has been investigated. It is shown that for the materials LnBa2Cu3Ox, with Ln=Sm, Eu, Gd, Dy, Ho, Er and Tm, the oxygen vacancy phase with Tc=60 K exists, although for the materials with Ln=Nd and Yb the existence of the Tc=60 K phase is not clear. The onset Tc of the Tc=60 K phase changes slightly depending on Ln involved in LnBa2Cu3Ox, Analysis of these data includes the determination of the lattice constants of the materials quenched at different temperatures.  相似文献   

2.
The structural and magnetic properties of the alloy system REIn0.5Ag0.5 [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 GdIn0.5Ag0.5 is ferromagnetic (Tc = 118 K), TbIn0.5Ag0.5 and DyIn0.5Ag0.5 are meta magnetic (TN = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (TN) 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.  相似文献   

3.
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.  相似文献   

4.
The main results of a model for 5d electrons in the heavy rare earth metals are presented. The model involves the use of wave functions based on published analyses for 4fn5d6s2 atomic configurations, and the spreading of each of these energy levels uniformly over a band of width W in the metals. Excess saturation magnetic moments above those of the tripositive ions can be explained by the model with W in the range 0.84±0.16eV in the five metals Gd, Tb, Dy, Er and Tm. The magnetic hyperfine fields in the metals include negative contributions from the 5d electrons which have been shown to amount to about ?250koe in Gd, Er and Tm.  相似文献   

5.
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 (μeff = 0.7 BM) compare well with the ideal Van Vleck behavior of Sm3+ ions with a J = 52 ground state and a low-lying excited first level J = 72. 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.  相似文献   

6.
The pressure dependence of the Young's and shear moduli of RFe2 (R = Sm, Gd, Tb, Dy, Ho and Er) has been determined at room temperature in the pressure range between 0 and 1 GPa The elastic moduli of GdFe2, DyFe2, HoFe2 and ErFe2 show a moderate increase with increasing hydrostatic pressure However, the elastic moduli of SmFe2 and TbFe2 exhibit an initially drastic increase followed by a high, and linear, pressure dependence From the pressure and temperature derivatives of the elastic moduli of these RFe2 Laves phase compounds the equations of state and the Gruneisen parameters have been derived The variation of the elastic properties with hydrostatic pressure is compared with the effect of magnetic fields The anomalous behavior of SmFe2 and TbFe2 is discussed.  相似文献   

7.
Samples whose dominant phase is R5Fe18B18 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Lu) were prepared by arc melting and vacuum annealing.Low temperature differential susceptibility measurements on Nd5Fe18B18 indicate a ferromagnetic transition at T ≈ 14K and perhaps a second magnetic transition at T ≈ 7K whose nature is not yet clear. Magnetic transitions were also observed in materials with R = Pr, Sm, Gd, Dy, Ho.Room temperature 57Fe Mössbauer measurements showed all samples to be paramagnetic; the quadrupole splitting and isomer shift were determined. Low temperature Mössbauer measurements indicate no magnetic ordering of Fe down to 1.5 K.  相似文献   

8.
用X射线衍射和磁测量手段研究了Ni部分替代Fe对具有ThMn12结构的Rfe11.3Nb0.7(R=Gd,Tb,Dy,Ho,Er和Y)化合物的结构与磁性的影响.研究表明,Ni部分替代Fe不改变晶体结构,但引起了晶胞体积收缩.随着Ni含量的增加,居里温度TC迅速上升,而饱和磁化强度Ms则单调减小.Ni部分替代Fe还导致了Fe次晶格的轴各向异性的迅速降低和RF11.3Nb0.7(R=Tb,Dy,Er)化合物中自旋重取向温度Tsr的变化.Tsr与Ni含量的关系用晶场理论给出了定性的解释. 关键词:  相似文献   

9.
代云雅  杨莉  彭述明  龙兴贵  周晓松  祖小涛 《物理学报》2012,61(10):108801-108801
采用第一性原理方法详细研究了氟化钙结构的多种金属氢化物MH2 (M= La, Nd, Gd, Tb, Y, Dy, Ho, Er, Lu, Sc, Ti, Zr, Hf)的力学性质(弹性常数、体弹模量、剪切模量、杨氏模量).计算结果表明, MH2 (M= La, Nd, Gd, Tb, Y, Dy, Ho, Er, Lu, Sc)在低温下具有稳定的氟化钙结构,其抵抗体积形变, 切应变和拉伸(或压缩)形变的能力从LaH2, NdH2, GdH2, TbH2, YH2, DyH2, HoH2, ErH2, LuH2到ScH2逐次递增, 而MH2 (M= Ti, Zr, Hf)在低温下的氟化钙结构不稳定.通过对两种稳定的氢化物(TbH2, ErH2) 和两种不稳定的氢化物(TiH2, HfH2)的电子态密度以及差分电荷密度进行对比, 发现它们的稳定性与金属和氢之间的相互作用有密切关系.  相似文献   

10.
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.  相似文献   

11.
We present the electrical resistivity measurements of equiatomic RPt compounds, with R  La, Pr, Nd, Gd, Tb, Dy, Ho and Er, which crystallize into two different orthorhombic structures. The different contributions to the total resistivity were separated. From the phonon contribution ϱp we estimated the Debye temperature θD of the different compounds. Except for GdPt, the increase of the magnetic resistivity above Tc arise from crystal field effects which are larger than those calculated in the point charge model. The paramagnetic Curie temperature and the saturated magnetic resistivity follow approximately the de Gennes law and allowed us to estimate effective mass and the exchange constant through the series.  相似文献   

12.
The systems RFe6Al6(R = Y, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) crystallize in the tetragonal body centered I4/mmm structure. In striking contrast to the magnetic behaviour of RFe4Al8 (weakly coupled R and Fe sublattices, complicated magnetic structure, low Tc ~ 130 K), in the RFe6Al6 systems all magnetic sublattices order simultaneously at a relatively high temperature. The magnetization curves start with low values at low temperatures and rise to very high values at Tmax ~ 230 K and then drop to 0 at Tc ~ 330 K. All samples show strong hysteresis effects at temperatures just below Tmax. Mossbauer studies of 57Fe in the (f) and (j) sites and 151Eu, 155Gd, 161Dy, 166Er and 170Yb in the (a) site yield all hyperfine interaction parameters and temperature dependence of the local magnetic moments. All Mossbauer and magnetization experimental results can be explained in a self consistent way with a simple molecular field model. The Fe in the (j) site plays the dominant role in its strong intrasublattice ferromagnetic exchange and its strong antiferromagnetic exchange with the rare earth site. The Fe in the (f) site have an antiferromagnetic intrasublattice exchange, they have a canted strcuture with the ferromagnetic component parallel to the (j) sublattice magnetization.  相似文献   

13.
Measurements of hyperfine interactions at 155Gd nuclei in metallic compounds between Gd and 3d transition metals and at 61Ni in GdNi compounds by Mössbauer spectroscopy are reported. The results are discussed in terms of various models proposed for the electronic structure of these compounds. The Gd isomer shifts with respect to metallic Gd are at variance with the model of a strong d electron transfer from rare earths to transition metal ions. From the observation of a linear relation between magnetic hyperfine fields at Gd and at Dy nuclei in corresponding compounds it is inferred that crystal-field induced variations of Dy moments are neglible and that the conduction electron polarization induced by 4f moments is directly related to that caused by 3d moments.  相似文献   

14.
Elastic properties, thermal expansion coefficients and electronic structures of Ti0.75X0.25C carbides (X=W, Mo, Ta, Nb, V, Hf, Zr, Cr and Al) were systematically investigated using ab initio density functional theory (DFT) calculations. The calculated elastic moduli, electronic structures and thermal expansion coefficients α(T) of pure TiC are in good agreement with experimental data and other DFT calculations. Based on a phenomenological formula, the trends of elastic properties and ductile/brittle behavior of Ti0.75X0.25C were analyzed. It was found that alloying elements W, Mo, Ta, Nb, V and Hf can increase elastic moduli, while Zr, Cr and Al reduce moduli. The nearly free electron model and Debye approximation were applied in the evaluation of α(T). The anharmonic effect was taken into account by including volume-dependent elastic moduli and Debye temperature. Results show that alloying additions of 3d V, 4d Zr and Mo slightly reduce α(T), while 3d Cr increases α(T), Al, 4d Nb, 5d Hf and W almost keep α(T) unchanged in Ti0.75X0.25C at high temperatures. The electronic structures of Ti0.75X0.25C were calculated and analyzed, and the electronic density of states was used to interpret variations of elastic properties and ductile/brittle behavior induced by alloying additions.  相似文献   

15.
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.  相似文献   

16.
A theory of bandwidth anisotropy in metallic ferromagnets developed previously is specialised to the case of 5d electrons in a hexagonal close-packed lattice. This theory is combined with a model for 5d electrons in the heavy rare earth metals to give a new theory for the low temperature values of the magnetic anisotropy coefficientsκ 2 0 andκ 4 0 in Tb, Dy, Ho, Er and Tm. In this theory the magnetic anisotropy is due to a combination of (i) crystal fields acting on 5d and 4f electrons and (ii) bandwidth anisotropy associated with a dependence of 5d bandwidths on magnetization direction. After use is made of empirical upper limits on the eighth order magnetic anisotropy in Gd, there remain four partially adjustable parameters of importance in the theory. These can be chosen to give a good fit to the six observed values forκ 2 0 andκ 4 0 in Tb, Dy and Ho. Crystal fields corresponding to negative point charges are seen by 5d electrons, but because of 4f – 5d interactions effective fields of larger magnitude and opposite sign act on 4f shells. Bandwidth anisotropy gives a significant contribution toκ 4 0 of opposite sign to that due to crystal fields, and dominates the latter in Tb and Er.  相似文献   

17.
《Physics letters. A》1997,229(4):259-261
Positron lifetime and Doppler broadening of the annihilation line measurements have been performed at room temperature in high-Tc superconductors RBa2Cu3Oy, where R: La, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er and 6.9 < y ≤ 7. Doppler broadening of the annihilation line measurements have also been performed in high-Tc superconducting samples R RBa2Cu3Oy, where R: Nd, Sm, Eu, Ho, Y, Er as a function of temperature between 14 K and 293 K. It was observed that the positron lifetime and the S parameter values at room temperature have no obvious trend in their variation from the yttrium substitution by a rare-earth element. It was also observed that the temperature dependence of the positron annihilation parameters is similar in the high-Tc superconducting samples.  相似文献   

18.
The pressure derivatives of the elastic constants cij of orthorhombic Li2Ge7O15 have been determined at 293 K by the method of pressure-induced shifts of resonance frequencies of thick plates at ca. 15 MHz in the range between 0 and 1500 bar. Approaching the transition at ca. 630 bar, all Pij = dcij/dp (i, j = 1, 2, 3; p pressure) develop strongly negative values. At higher pressures a similar behaviour with reversed sign is observed. The pressure derivatives of the pure “shear resistances” c44, c55, and c66 depend only slightly on pressure even in the vicinity of the transition. The main interactions driving the transition are of the totally symmetric type. The values dK?1/dp (K volume compressibility) deviate strongly from the quasi-invariant value of ca. 5 observed in almost all stable crystals (dK?1/dp = ? 1750 at 620 bar and 1380 at 700 bar). The anomalous piezoelastic behaviour reflects the anomalous thermoelastic behaviour: negative Pij in the low pressure (high temperature) phase correspond to positive Tij = d log cij/dT (T temperature) and vice versa.  相似文献   

19.
Tetragonal R1+εFe4B4 alloys with R = Gd and Dy have been investigated by Mössbauer spectroscopy, using the 155Gd and 161Dy resonances, respectively. The Gd quadrupolar interaction e2qQ = 12.65(5)mm/s is the largest observed to date in metallic compounds of Gd. For Dy this interaction is e2qQ = 74(2) mm/s, a value rather small for a Dy compound. Both results imply a strong lattice contribution to the electric field gradient. A crystal-field term A02 = -2450(50) K/a2o is inferred. Our data are consistent with a point-charge calculation, provided charges of opposite signs are assumed for Fe and B atoms. Hyperfine parameters show some dispersion, reflecting the quasi incommensurate nature of the R and Fe+B sublattices in the R1+εFe4B4 structure.  相似文献   

20.
The systems RM6Al6 (R = rare earth or Y, M = Cr, Mn, Cu, Rh) were studied by magnetization measurements and by Mossbauer spectroscopy of 155Gd, 161Dy, 166Er and 170Yb. The magnetization studies show weak R-R antiferromagnetic exchange interactions in RCu6Al6(Tn)Gd) = 21 K, less than 4 K for all other R and strong crystalline field effects. Similar phenomena are observed in RMn6Al6 and RCr6Al6, however, due to the presence of a Mn or Cr local moment the systems order ferrimagnetically. In RCr6Al6the order temperatures are low Tc ~ 25 K, yet Tc(GdCr6Al6) = 170 K. The Mossbauer studies observations are consistent with the magnetiza results. In the case where Er and Yb are not ordered at 4.1 K, the spectra still show magnetic hyperfine structure however of paramagnetic nature. The spectra yield the hyperfine interaction spin Hamiltonian parameters and the spin relaxation rates. These turn out to be extremely slow (1O8–1O9 sec?1, a very uncommon phenomenon for a concentrated Er or Yb metallic system.  相似文献   

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