La-Ce Alloys Research Articles

Strategy to improve magnetic property of sintered (Nd, Ce)–Fe–B magnets: Moderate replacement of cerium with lanthanum

In this work, we proposed a method to enhance the magnetic properties of (Nd, Ce)–Fe–B magnets with Ce/TRE ratios below 25 wt% by introducing a moderate amount of La elements. The segregation behavior of La elements towards grain boundaries (GBs) was utilized to optimize the GB phase structure. Incorporation of La atoms into the main phase induces lattice expansion, leading to an increased formation of Ce3+ ions with enhanced magnetic moments. Comparative analysis with the original magnet (La/Ce = 0 wt%) demonstrates that the magnet with a La/Ce ratio of 10 wt% exhibits improvements of 0.3% in remanence, 12.6% in coercivity, and 0.6% in maximum energy product. These results underscore that the moderate addition of La elements enhances the fluidity of the rare earth-rich phase and optimizes the distribution of lamellar GB, consequently reinforcing the magnetic isolation effect. Furthermore, the promotion of the transformation from Ce4+ to Ce3+ ions contributes to the comprehensive enhancement of the magnetic properties. This research offers a novel strategy for fabricating high-performance and resource-efficient sintered magnets based on LaCe alloys.

First-Principles Investigations on Structural, Elastic, and Thermodynamic Properties of Ce-La Alloys Under High Pressure

The structural stability, thermodynamic, elastic, and electronic properties of cerium (Ce)- lanthanum (La) alloys were investigated for different Ce/La ratios under pressure by first-principles calculations using on-the-fly (OTF) pseudopotential and general gradient approximation (GGA). The ground-state properties of lanthanum and cerium obtained by minimizing the total energy agree favourably with other work.We derived the elastic constants, bulk modulus, and shear modulus of the La-Ce alloys for different Ce/La ratios. Using the quasi-harmonic Debye model, the thermodynamic properties of the La-Ce alloys including the thermal expansion coefficient α and heat capacity Cv are successfully obtained in the temperature range from 0 K to 1000 K. Furthermore, the electronic properties such as density of states and charge densities were also studied.

Phase analysis of Mg–La–Nd and Mg–La–Ce alloys

The ternary solubilities and solidification details of the Mg–Nd–La and Mg–La–Ce systems were examined through the evaluation of two alloys from each system. Thermodynamic parameters of the two systems were optimized using the observed phase constituents and measured ternary solubilities by SEM combined with the DSC signals of the four alloys. Isothermal sections at 500 °C and solidification paths of the two systems were evaluated.

Pressure-induced magnetic phase transition (spin glass → Kondo) in [formula omitted]Ce alloys

In most spin glass systems the freezing temperature T o lies well above the Kondo temperature T K. The relatively rapid increase of T K caused by pressure should lead to a spin glass to Kondo phase transition as predicted by Larsen. Evidence for such a transition has been found in high pressure resistivity measurement on La Ce alloys.

Intermediate-temperature superconductivity of the kondo system [formula omitted]Ce under hydrostatic pressure

The superconducting transition temperature T c of La Ce alloys (<3 at .% Ce) was measured as a function of hydrostatic pressure (up to 12 kbar) in the temperature range between 80 mK and 6K. Alloys with 2 at .% Ce show the striking phenomenon of re-entrant superconductivity in the pressure range of 6–8 kbar.

Hyperfine Interaction Studies of Local Moments in Metals

The aim of this article is to describe hyperfine measurements on dilute magnetic alloys. We discuss only single impurity effects. The study of a paramagnetic impurity in a non-magnetic host is split into two parts: first the weak resonant coupling corresponds to a well isolated magnetic moment, secondly the strong resonant coupling corresponds to a situation where the Kondo or the spin fluctuation temperature is an order of magnitude greater than the experimental temperature. After a brief summary of the theoretical problems and some remarks on the possibility of the radioactive measurements, we restrict the experimental review to few cases: study of the Au Yb and Cu Fe alloys by Mössbauer effect (M.E.), study of the Pt CO, Au CO and La Ce alloys by nuclear orientation experiments (N.O.).

Skew scattering in alloys with cerium impurities

Skew scattering by magnetic impurities in dilute magnetic alloys induces an extraordinary Hall effect which has now been observed in many systems. The author calculates the extraordinary Hall effect induced by cerium impurities for which the conduction electron-impurity interaction is mainly due to resonant scattering. The results are compared with experimental data on La-Ce alloys. The anisotropy of the magneto-resistance of such alloys is calculated and compared with some preliminary experimental results.

High pressure resistance measurements of some lanthanum-cerium alloys

The room temperature, high pressure resistances of some La-Ce alloys have been studied in the present work. The pressure of the resistance anomaly associated with the γ→ α phase change in pure cerium (f.c.c.→ f.c.c.) increases smoothly with increasing lanthanum content from a value of 7 kB for cerium to about 25 kB for lanthanum. This suggests that the resistance anomaly in pure lanthanum could be associated with an electronic change similar to that observed in cerium, rather than due to the d.hex.→ f.c.c. structural change. The pressure at which the resistance anomaly associated with the α→ α′ change in cerium occurs increases rapidly with increasing lanthanum content and the magnitude of the effect decreases such that it cannot be detected at above 40 % lanthanum, indicating a possible critical point for this transformation.

Pair-breaking effects in the superconducting Kondo alloy LaCe

The depression of the superconducting transition temperature of LaCe alloys and the upper critical fieldHc2(T) of La and LaCe was measured, down to 0.05 K. The results disagree with calculations, based on recent theories, including the temperature dependence of the spin-flip amplitude.

Pressure dependence of the Kondo resistance anomaly and the pair breaking effect in La-Ce alloys

The pressure dependence of the parr breaking effect and of the resistance anomaly was measured in LaCe alloys. The results indicate that the maximum in the pressure dependent pair breaking effect is due to a monotonic shift of the Kondo temperatureTk with pressure from valuesTk> ≪Tc0 toTk ≫Tc0, whereTc0 is the superconducting transition temperature of pure lanthanum.

Superconductivity and Magnetic Order in La–Ce Alloys

Superconductivity and magnetic order have been studied both above and below the Kondo temperature for the La–Ce system. Electrical resistivity measurements on La 0.2, 1.0, 2.0, 3.2, and 4.0 wt% Ce have been made from 0.060 to 20.0 K. All samples showed a Kondo-like minimum Tmin in the resistivity with a subsequent maximum Tmax. Tmin was found to be proportional to n1/7, where n is the concentration, and Tmax(H=0) was proportional to n2. The resistivity due to the magnetic impurities went as αln (T/T0) on both sides of Tmax. Above Tmax, α was almost independent of n, and below Tmax it was proportional to n2. Applied magnetic fields had little effect on α even through Tmax increased linearly with H. The magnitude of the resistivity at the peak was essentially independent of n, but decreased for increased H. The superconducting transition temperature was depressed as n increased, but more slowly than predicted by Abrikosov and Gor'kov, and the critical field curves were considerably depressed below the multiple pair breaking theory of Fulde and Maki.

Note on the Kondo Temperature of La-Ce Alloys

Note on the Kondo Temperature of La-Ce Alloys

Spin Compensation in an Element, Cerium

The low-temperature susceptibility above the magnetic ordering temperature of La-Ce alloys (Ce concentration \ensuremath{\le} 40 at%) and of $\ensuremath{\alpha}$-Ce and $\ensuremath{\beta}$-Ce is proportional to ${T}^{\ensuremath{-}\frac{1}{2}}$. This is the temperature dependence recently suggested by Anderson in the case of spin compensation. The susceptibility per Ce atom for the alloys above the magnetic ordering temperature is independent of Ce concentration. It is suggested that these systems exhibit spin compensation.

Low Temperature Resistivity, Magnetic Susceptibility, and Superconducting Transition Temperature in Lanthanum Containing Rare-Earth Impurities

The resistivities and the magnetic susceptibilities of lanthanum containing small amounts of other rare-earth metals have been measured at low temperatures. Resistance minima have been found at about 6.5°K in fcc La-Ce alloys and at about 5.8°K in hcp La-Ce alloys. The temperature at which the resistance minimum occurs is independent of the concentration of Ce. Any minimum has not been found in the alloys with solutes other than Ce. The observed resistivity of all the alloys contains a term proportional to log T in accordance with the recent theories on the s - d or s - f resistivity due to Kondo and others. The magnetic susceptibilities of La-Ce, La-Pr, and La-Nd alloys are not inconsistent with the resistive behaviors of these alloys. The effective s - f exchange integrals for various rare-earth solutes have been calculated from the resistivity data and compared with those calculated from the change of the superconducting transition temperature of La due to added rare-earth metals. The agreement between...