Magnetoelastic coupling in dilute rare earth alloys

A model for coupling between Rare Earth ion and the lattice via conduction electrons is presented. It should be useful in explaining large magnetostriction effects in rare earth metals and their alloys.     

Amorphous rare earth alloys: Random-anisotropy ferromagnetism in the pair approximation

A self-consistent two-spin cluster approximation is used to calculate magnetization curves and correlation functions for a ferromagnetic amorphous alloy within the random-anisotropy model for the case of unit total angular momentum (j = 1) and correlations between the anisotropy axes.     

Charged particle erosion of solid rare gases and dilute rare gas alloys

We present the first experimental results on electron-induced erosion of solid neon. The measurements are interpreted qualitatively within a new model invoking excitation transport by free excitons and their subsequent decay at the surface. The model accounts for the magnitude of the observed yield and the energy dependence. A theoretically predicted decrease in the erosion yield due to doping with a heavier rare gas, in casu argon, has been observed experimentally. The strong influence of very small amounts of different types of impurities makes sample purity a crucial problem in investigations of the erosion of solid rare gases.     

Magnetic coupling of rare earth moments in amorphous alloys

Several amorphous Gd alloys containing about 75 at % Gd were prepared, the second component being Al, Cu, Ga, Rh or Pd. All these alloys were found to be ferromagnetic with quite similar ordering temperatures. Possible coupling mechanisms between the localized moments are discussed. It is shown that the RKKY coupling scheme can only be of minor importance in these alloys.     

Spin structure of some Sm-phase light-heavy rare earth alloys

The magnetic structures and ordered moments of alloys between Tb, Dy and Ho and Pr and Nd have been determined from neutron diffraction data on polycrystalline samples. The observed magnetic scattering is discussed in terms of the ordering on the hexagonal and cubic sites, respectively.     

Magnetic properties of some hcp light-heavy rare earth alloys

The magnetic properties of alloys between Tb, Dy and Ho and Pr and Nd have been studied in the hcp structure. Their properties may be understood in terms of the change of the effective de Gennes factor and the axial ratio on alloying.     

On the origin of rare earth magnetostriction in compounds of perovskite-type structure

It has been shown that a gigantic rare earth magnetostriction is possible in a perovskite-type structure as well as in a garnet structure. Numerical calculations of multipole moments of the rare earth ion have allowed us to predict the directions of maximum values of magnetostriction in dysprosium aluminate. Measurements confirm the highly anisotropic character of magnetostriction in rare earth compounds of perovskite-type structure and show that the rare earth magnetostriction of compounds with different structures (garnets, perovskites) is determined mainly by the rare earth ion and not by their structures.     

Theory of solid solubility for rare earth metal based alloys

Both parabola and ellipse separating schemes are used to study the solid solubilities for the binary alloy systems based on the 13 rare earth metals. It has been found that the soluble elements can be separated from the insoluble ones by a parabolyy ₁=a?bx ₁ ² or an ellipse(x ₂?m)²/c²+(y₂?n)²/d²=1. The results show that the overall reliabilities of the solid solubilities for the 897 binary alloys based on the rare earth metals are 89.2% and 92.8% for the parabola and ellipse regularities respectively. The constants a and b in the parabola equation, andm, n, c andd in the ellipse equation are discussed, which can be related to some appropriate parameters for each host metal respectively.     

Theory of solid solubility for rare earth metal based alloys

Both parabola and ellipse separating schemes are used to study the solid solubilities for the binary alloy systems based on the 13 rare earth metals. It has been found that the soluble elements can be separated from the insoluble ones by a parabolyy ₁=a−bx ₁ ² or an ellipse(x ₂−m)²/c²+(y₂−n)²/d²=1. The results show that the overall reliabilities of the solid solubilities for the 897 binary alloys based on the rare earth metals are 89.2% and 92.8% for the parabola and ellipse regularities respectively. The constants a and b in the parabola equation, andm, n, c andd in the ellipse equation are discussed, which can be related to some appropriate parameters for each host metal respectively.     

Magnetoelastic effects in rare earth metals and alloys near magnetic phase transitions

Magnetoelastocaloric effects in rare earth metals and alloys have been thermodynamically investigated. It is found that these magnets, along with the ordinary elastocaloric effect, exhibit a giant magnetoelastocaloric effect near the magnetic ordering temperatures, which is proportional to the temperature derivative of spontaneous magnetostriction.     

Pressure effects on the superconductivity of ternary rare earth palladium Heusler alloys

The application of hydrostatic pressure linearly depresses the superconducting transition temperature with a typical rate of dT_c/dP ～10^-5 K/bar for the Heusler alloys RPd₂Z, where R=Sc, Y, Tm, Yb, Lu and Z=Sn, Pb. This depression can be explained by a stiffening of the primitive cubic palladium sublattice with increasing pressure.     

Infrared and ESR spectroscopy of KTaO3 : Er

Infrared reflection and ESR spectra of KTaO₃ : Er³⁺ single crystals have been investigated. The frequency of the lowest optical phonon mode TO₁ has been found to increase as compared to undoped KTaO₃ crystals, which indicates the suppression of the ferroelectric instability of the system. The ESR spectra have revealed the presence of two Er³⁺ centers of different (cubic and non-cubic) symmetries in KTaO₃ : Er³⁺.     

Structural transformation studies on the rare earth containing Heusler alloys Pd2RESn

The Heusler alloys Pd₂RESn form for rare-earths (RE) from Tb to Lu and for Sc and Y. Of these, the alloys containing Yb, Tm, Lu, Sc and Y are superconducting. We have carried out structural studies on all these alloys by studying the temperature dependence of the X-ray patterns in the temperature range 5 to 300 K. Some nonstoichiometric compositions were also investigated. Structural transformation is observed only in Tb and Dy containing alloys while none of the superconducting alloys show a transformation. The transformation temperature is lowered by about 50 K in going from stoichiometric Pd₂TbSn to nonstoichiometric Pd₂Tb_0.95Sn while it is completely suppressed in Pd₂Dy_0.95Sn. Magnetic and Mössbauer studies on Dy compound are also reported.     

On the Tc of dilute alloys

The equation for the critical temperature T_c, of a dilute superconducting alloy due to Markowitz and Kadanoff (MK) is generalized to include renormalization effects due to the electron-phonon interaction. Such corrections constitute a 50% effect in weak coupling superconductors like aluminum while in strong coupling systems like lead this correction gives a factor of 2.5. The mean square anisotropy parameter appearing in the T_c equation is also generalized to remove the separability assumption of the electron-phonon interaction. Some consequences of these two corrections to the analysis and systematization of data for dilute superconducting alloys is discussed.     

On the magnetoresistance in dilute magnetic alloys

Many-particle contributions to extended Suhl equations are considered to derive a magnetoresistance, which saturates for nonzero magnetic fields below the unitatarity limit in agreement with experiments.     

The influence of hexagonal anisotropy on the magnetic structure of antiferromagnetic rare earth metals and alloys

The effect of hexagonal base plane anisotropy on the antiferroniagnetic (AF) spiral spin structure of rare earth metals and alloys has been investigated. Minimization of the anisotropy energy is considered either by a reorientation of rigid coherent sections of the spiral or by a continuous modulation of the spiral periodicity. Both results indicate that when the spiral periodicity is commensurate with the hexagonal anisotropy the energy is greater than for spirals which are non-commensurate. The calculations predict that when the temperature is varied in the AF phase, the magnetic structure becomes unstable as a commensurate turn angle is approached, which may provide a qualitative explanation for the abrupt changes in the c-axis thermal expansion and temperature dependence of the elastic constant C₄₄ that have been observed experimentally in dysprosium and terbium-50% holmium. Further consequences of the spiral perturbation by hexagonal anisotropy are considered.     

Anisotropic thermal expansion of yttrium metal and yttrium-based rare earth alloys at low temperature

We report on thermal expansion measurements at low temperatures of pure Y and RE (RE: Er, Dy, Tb and Gd) single crystals. We estimate the electronic and lattice contributions for the thermal expansion of pure yttrium. For the dilute RE alloys, the thermal expansion exhibits crystal field effects. These are explained with a free energy including crystal field, elastic and magnetoelastic terms.     

Formation of Tsai-type 1/1 approximants in In-Pd-RE (RE: rare earth metal) alloys

The formation of the 1/1 crystal approximant phase (1/1 phase) to the icosahedral phase (i phase) in In-Pd-RE (RE: rare earth metal) systems has been investigated. A new series of 1/1 phases were found in In₅₃Pd₃₃RE₁₄ (RE; Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) alloys. For Y, Sm, Gd, Tb, Dy, and Ho, the 1/1 phases were found in annealed alloys, indicating that they are thermodynamically stable. The atomic structure of the 1/1 phases was directly observed by high-angle annular dark-field imaging performed via scanning transmission electron microscopy, revealing that the 1/1 phases consisted of a periodic arrangement of Tsai-type icosahedral clusters. Further, the atomic size effect on i phase formation, as well as formation conditions previously reported for other Tsai-type i and 1/1 phases were examined. It was found that the ratio of the atomic radius of base metals such as In and Pd affects i phase formation. Moreover, the appropriate range of the radius ratio for i phase formation was narrower than that for 1/1 phase formation.     

ZA27合金中稀土及铁的晶界偏聚与交互作用

根据分子动力学理论建立了液态ZA27合金的原子集团，结合计算机编程构造出ZA27合金α相与液相共存时的原子构形及α相大角度重位点阵晶界模型.利用递归法计算了铁、稀土元素 固溶 于晶粒内，游离于固液相界面及其在α相晶界处的环境敏感镶嵌能，计算了铁、稀土元素与 Al 的键级积分.由此得出：铁、稀土处于固液相界区比在晶内更稳定，解释了铁、稀土在α相内溶解度很小，结晶时富集于固液相界前沿液体中，从而导致凝固结束后铁、稀土元素偏聚于晶界，并形成成分复杂的稀土化合物的事实. 关键词： 稀土 晶界 递归方法 电子结构