Effect Of Rare Earth Substitution Research Articles

Magnetic properties of Fe‐(Nd, Sm)‐B amorphous alloys

AbstractThe magnetization behaviour of amorphous alloys Fe80–xRExB20 (RE = Nd, Sm) with 0 ≤ x ≤ 16, prepared by melt‐spinning technique. The effect of rare earth substitution on the magnetic properties (Tc, M 0, Hc …) of amorphous alloy has been investigated. Using Random Magnetic Anisotropy Model (RMA), we have analysed our results and obtained some fundamental parameters. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Power factors of late rare earth-doped Ca 3Co 2O 6 oxides

Polycrystalline samples of (Ca 1− x R x ) 3Co 2O 6 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 Gd 3+>Tb 3+>Dy 3+>Ho 3+. 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 Ho 3+ for Ca 2+. For the Ho-doped samples ( x ≤ 0.05 ) , the power factor was significantly improved by increasing Ho concentration.

Effect of Rare Earth Substitution on Machinability of R-Fe-B Sintered Magnets

The machinability of sintered Nd-Fe-B magnets with nominal compositions of (Nd 1–xDy x) 16Fe 78B 6 ( x = 0, 0.05, 0.10, 0.15) and (Nd 1–yPr y) 16Fe 78B 6 ( y = 0, 0.33, 0.67, 1), has been investigated. The bending strength, fracture toughness and the Vickers Hardness were measured. It shows that the Dy substituted magnets shows higher Vickers Hardness than the Pr substituted magnets. The brittle index for investigated magnets improves monotonously with increasing Dy content, reduces with increasing Pr content, respectively, which seems to relate closely to the change of the lattice parameters.

The effect of rare-earth substitution at the Ba site on the flux pinning properties of Y(Ba 2− xR x)Cu 3O 7− δ (for R=La, Pr, and Nd)

The behavior of the critical current density ( J c) and critical temperature ( T c) with rare-earth substitution at the Ba site in Y(Ba 2− x R x )Cu 3O 7− δ (0⩽ x⩽0.15) (for R=La, Pr, and Nd) has been investigated. In the case of magnetic rare-earth substitutions (Pr and Nd), a specific secondary peak appears and grows in the J c– H curves with increasing x, whereas no such peak emerges in a case of nonmagnetic rare-earth (La) substitution. This result suggests that the magnetic moment at the Ba site is an important factor generating defects that act as effective “field-induced type” pinning centers. However, the magnetic moment does not directly affect the variation in T c. That is, while the T c of Pr-substituted samples decreases monotonically with increasing x, the T c of Nd-substituted samples exhibits a maximum at low x (∼0.05), as is the case for La-substituted samples. Accordingly, Nd substitution is considered to be the most effective way of enhancing J c, because of its ability to generate defects that can act as effective pinning centers without inducing any noticeable suppression of superconductivity in the matrix.

The effect of rare earth substitution on the magnetic properties of Ni0.5Zn0.5MxFe2−xO4 (M: rare earth)

Variation of the complex permeability with frequency of Ni 1− x Zn x Fe 2 O 4 ( x =0.5, 0.6 and 0.7) prepared by a combustion method has been measured over a wide range of frequency, up to 1.8 GHz. Zn content improves permeability but moves the onset of resonance to lower frequencies. The influence on some properties of samples prepared by the insertion of small amounts of Ruthenium, Yttrium and rare-earth cations into the Ni 0.5 Zn 0.5 M x Fe 2− x O 4 ferrite has been also investigated. Relative losses and Curie temperature of all the samples have been measured. Ferrites substituted with Ru and Gd improve microwave behavior compared to non-substituted samples.

Amorphous magnetic RE-Fe-Al alloys

Detail studies of the effects of rare-earth substitution on the magnetic properties of bulk amorphous hard magnetic Nd/sub 60/Fe/sub 30/Al/sub 10/ alloys were carried out. Amorphous ribbons of alloys RE/sub 60/Fe/sub 30/Al/sub 10/ (with RE=Nd,Sm,Gd and Dy) were prepared by melt-spinning at 30 m/s. As temperature increases, instead of just a simple transition from ferromagnetic state to paramagnetic state, these ribbons undergo a superparamagnetic stage that ranges over about 100 K. Ribbons of alloys RE/sub 60/Fe/sub 30/Al/sub 10/ with RE=Nd,Sm and Dy exhibit high values of coercivity (in MA/m) range at 4 K, while coercivity of ribbons of alloys with RE=Y and Gd remain low below 100 kA/m.

Effects of rare-earth substitution in : mixed-valence and magnetic properties

The lattice parameters and magnetic properties of (R = Ho, Er) have been investigated. The deviation of the lattice parameters from Vegard's law indicates that the Ce valence in both systems fluctuates with the concentration of the dopant R. This fluctuation is directly relevant to the degree of localization of Ce 4f electrons, and is independent of the atomic size of the dopant element. The observed metamagnetic transition of has been analysed from the description in the band picture. The Ce valence fluctuation from the mixed-valence state to the localized state increases the moments of the Ce and Fe ions, and the Curie temperature. The changes in the mixed-valence state also affect the properties of the Ce-Fe coupling.

Systematic Raman study of effects of rare-earth substitution on the lattice modes of high-Tc superconductors.

We report on the effect of rare-earth substitution on the Raman spectra of $R{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ perovskites where $R=\mathrm{Y},\mathrm{La},\mathrm{Pr},\mathrm{Nd},\mathrm{Sm},\mathrm{Eu},\mathrm{Gd},\mathrm{Dy},\mathrm{Ho},\mathrm{Tm},\mathrm{and} \mathrm{Lu}$. These spectra show both the presence of Raman modes that are intrinsic to the superconducting material and also those due to impurity phases. The intrinsic Raman modes near 340 ${\mathrm{cm}}^{\ensuremath{-}1}$ and 500 ${\mathrm{cm}}^{\ensuremath{-}1}$ which have been attributed, respectively, to Cu(2)-O(2,3) bending and Cu(1)-O(4) stretching vibrations, show substantial and systematic variations in vibrational frequency as a function of the ionic radius of the rare earth. These variations are in good agreement with neutron-scattering determinations of bond lengths, which supports the vibrational assignment of these modes. Pr${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ shows no anomalous behavior in its vibrational spectrum even though it was the only sample studied that was not superconducting. This suggests that the valency of Pr is similar to the other rare earths studied and cannot account for the absence of superconductivity in this material. Assignment of other Raman modes in the rare-earth spectra requires identification of impurity phases, which even in small concentrations, can significantly contribute to the Raman spectra. Impurity phases can be preferentially at the surface of samples and can be substantially modified by heat treatment in an argon atmosphere. These impurity phases have previously been confused with disorder-induced Raman modes.

Superconductivity in Bi2.2Ca2.8−x Sr x Cu2O y system and effect of rare earth substitution

The oxide system Bi2.2Ca2.8−xSrxCu2Oy has been investigated for superconductivity as a function of Ca/Sr ratio withx=0.7, 1.0, 1.4 and 1.8. All these compositions are found to be superconducting with onset temperature in the range of 80–90 K implying a large homogeneity range between Sr and Ca for the superconductivity to occur in this system. Effect of partial replacement of Bi by rare earths has been studied and it is observed that 20% replacement of Bi by Nd and Eu does not significantly affect the superconducting transition temperature.