Effect of high magnetic field on the morphology of (Cu, Ni)6Sn5 at Sn0.3Ni/Cu interface

The effect of high magnetic field on the microstructure of (Cu, Ni)₆Sn₅ intermetallic compound layer in Sn0.3Ni/Cu couples at 250 °C was examined. The applied magnetic field changed the morphology of outer (Cu, Ni)₆Sn₅ crystals on the Sn side from faceted shape to stick shape. The high magnetic field affected the crystal orientations of (Cu, Ni)₆Sn₅ and reduced the Ni content in the outer layer. The morphology evolution of (Cu, Ni)₆Sn₅ is attributed to the content of Ni solute decreased by magnetic field. The effects of high magnetic field on the liquid convection and phase diagram are considered to be responsible for the Ni content.     

Structure and electrical properties of liquid Sn,Sn0.962Ag0.038, Sn0.987Cu0.013, and Sn0.949Ag0.038Cu0.013

We have studied the structure, electrical conductivity, and thermopower of liquid Sn, Sn_0.962Ag_0.038, Sn_0.987Cu_0.013, and Sn_0.949Ag_0.038Cu_0.013 alloys, which are used as lead-free solders. Diffraction data have been used to develop structural models of the melts. The conductivity and thermopower data have been interpreted in terms of the proposed structural models and resonance s-d scattering. Original Russian Text ? S.I. Mudry, V.M. Sklyarchuk, Yu.O. Plevachuk, I.I. Shtablavyi, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 171–175.     

Thermodynamic properties of the Al-Eu-Sn melts

Mixing enthalpies of melts of the binary systems Al-Eu at 1300–1473 K (in the concentration ranges 0 < x _Eu < 0.2 and 0.57 < x _Eu < 1) and Eu-Sn at 1250–1300 K (0 < x _Sn < 0.2; 0.51 < x _Sn < 1) were studied for the first time by the isoperibolic calorimetry technique. It was determined that there are moderate (ΔH_min = ?23 kJ/mol at x _Eu = 0.39) and large (ΔH_min = ? 63 kJ/mol at x _Sn = 0.42) exothermic formation effects for these melts, correspondingly. Using the information obtained by us and taken from literature, thermodynamic properties of these melts were calculated in the wide temperature range by the model of ideal associated solutions (IAS). The mixing enthalpies of melts of the ternary Al-Eu-Sn system were modeled using the analogous data for the binary boundary systems.     

Interactions magnetiques hyperfines et quadrupolaires combinees pour les ions d'impuretes 119Sn2+ dans Cr2O3

Hyperfine magnetic interactions have been observed for the first time for Sn²⁺ ions introduced as doping agents in a magnetically ordered oxide (¹¹⁹Sn: Cr₂O₃). Mössbauer resonance at low temperature shows for ¹¹⁹Sn²⁺ the simultaneous presence of hyperfine magnetic and quadrupole interactions, which have the same order of magnitude at 77 K. From the spectra, the following parameters have been determined: tranfered hyperfine magnetic field: H_Sn²⁺ (77 K = 38 ± 1kOe, sign and value of the quadrupole interaction constant: eV_zzQ = + 3,6 ± 0,3 mm/s, asymmetry parameter: η = 0,15 ± 0,05, polar (θ) and azimutal (?) angles: $\text{θ ? ? ? 90°}$, and chemical shift: $\text{δ}\text{BaSnO}{}_3\text{= + 2,89 ± 0,02}\text{mm}\text{/}\text{s}$. The investigation shows that Sn²⁺ is localized at the surface of the Cr₂O₃ grains.     

Gilbert Damping Constant of Quaternary Co2MnAl1?x Sn x Heusler Alloy Thin Films

Polycrystalline quaternary Co₂MnAl_1?x Sn _x films with x=0.25, 0.5, 0.75,?1 were prepared at room temperature using magnetron sputtering technique on SiO₂ substrates and post-annealed at various temperatures. We investigated the crystal structures, magnetic properties, and magnetic damping constants (??) of the prepared films. Out-of-plane angular dependences of the resonance field and the linewidth of the ferromagnetic resonance spectra were measured and analyzed using the Landau?CLifshitz?CGilbert equation to determine the magnetic properties and damping constant. Co₂MnAl_0.75Sn_0.25 and Co₂MnSn films had A2 ordered crystal structure while Co₂MnAl_0.25Sn_0.75 and Co₂MnAl_0.5Sn_0.5 films had A2 ordering up to 400?°C and 300?°C annealing temperature, respectively, and they had B2 ordering for the remaining temperatures. Also the crystal structure deteriorated at 600?°C for all of the film systems. The saturation magnetization, M _S , of films increased with annealing temperature till 400?°C except Co₂MnAl_0.5Sn_0.5 in which M _S increased till 500?°C, which is consistent with the structural analysis. The effective magnetization was obtained from the FMR spectra and it was found that it decreased with increasing Sn-concentration and reached a minimum value at Co₂MnAl_0.25Sn_0.75 composition. Lastly, Co₂MnAl_1?x Sn _x films annealed at 500?°C showed the best crystal ordering. The lowest ?? value was 0.008 and obtained from Co₂MnAl_0.5Sn_0.5 films annealed at 500?°C.     

Elastic Properties of Superconducting Stannides: Yb3Rh4Sn13 and Ca3Rh4Sn13

We present an experimental investigation of the temperature and magnetic field dependence of the elastic constants in the two stannide compounds Yb ₃ Rh ₄ Sn ₁₃ and Ca ₃ Rh ₄ Sn ₁₃ . We find a small elastic softening of the c₄₄ mode of ca. 2% in the normal state. The temperature dependence of the various elastic modes are quite anomalous in the superconducting state. A comparison of our results is given with corresponding results of CeRu ₂ , an amorphous superconductor and other amorphous materials.     

Viscous feature of Sb-Bi alloy under magnetic field

Viscosity of SbBi melts under different magnetic induction intensity was investigated by using RHEOTRONI C VIII torsional oscillation viscometer with 0-0.27 T horizontal magnetic field. The viscosity of all melts measured decreased with increasing temperature under different magnetic intensity. Furthermore, the viscosity increased as horizontal magnetic intensity enhanced. The effect of magnetic induction intensity on the viscosity of melts increased with the content of Sb in the melts. The viscosity-temperature curves can be well fitted with Equation η = η₀ + AB².     

Direct observation of magnetostructural transition in the Ni–Mn–Sn alloy using in situ optical microscope

The microstructure evolution of the magnetic-field-induced transition in Ni_44.4Mn_44.8Sn_10.8 alloy was directly observed using in situ optical microscope under pulsed high magnetic field. The microscopic observations indicate that the growth of austenite during magnetic field application might be through the movement of the interface between martensite and austenite phases. This kind of induced austenite state is stable and remained even removing the magnetic field. Based on the experimental results, the change of the brightness contrast might be used to further investigate this irreversibility of the magnetostructural transition and determine the critical transition magnetic fields.     

Band edge motion in quantizing magnetic field and nonequilibrium states in Pb1−x Sn x Te alloys doped with In

Galvanomagnetic and oscillation effects in Pb_1–x Sn _x Te single crystals doped with 0.5 at % In have been studied in magnetic fields up to 60 kOe at temperatures from 4.2 to 30 K under hydrostatic pressure up to 18 kbar. Beyond the ultraquantum magnetic field limit (H _uql) for the metallic state of Pb_1–x Sn _x Te(In) alloys, Fermi level pinning by high-density quasilocal states takes place. In a strong fieldH>H _uql the equationE _F = const is valid instead of the equationn = const which is usual for degenerate semiconductors (E _F is the electron or hole Fermi energy, andn is their concentration). This makes it possible to determine the direction of the band edge motion in the Pb_1–x Sn _x Te energy spectrum in a quantizing magnetic field in the direct and inverse spectral regions. It is found that the charge carrier transitions between quasilocal and band states are of anomalously long duration (10⁵ sec atT=4.2 K). By the application of a quantizing magnetic field we obtained a nonequilibrium metallic state of the system with a frozen or slowly diminishing Fermi surface. The characteristic time of the transition was found as a function of temperature and pressure. The relaxation kinetics of the nonequilibrium states induced by a quantizing magnetic field and infrared irradiation is discussed.     

Metallic materials for superconductor stabilization with very high specific heat and good thermal conductivity

In a search for materials useful for enthalpy stabilization of technical superconductors we have performed specific-heat measurements on PrCu₂, PrB₆, NdSn₃ and Nd_0.9Pr_0.1Sn₃ between 3 and 10 K and in magnetic fields up to 7 T. Due to different types of phase transitions these compounds exhibit large peaks in the heat-capacity curves. In these materials the high specific heat values are not substantially reduced the the external magnetic fields, which makes them attractive for technical application.     

Ab-initio Calculation of Half-Metal Ferrimagnetic Sn0.9Mn0.05Co0.05O2

Based on first-principles spin-density functional calculations, using the Korringa?CKohn?CRostoker (KKR) method combined with the coherent potential approximation (CPA), we investigated the half-metallic ferrimagnetic properties of SnO₂ codoped with Mn and Co impurities (Sn_0.90(Mn_0.05, Co_0.05)O₂) within the self-interaction-corrected (SIC) local density approximation. Mechanism of hybridization and interaction between magnetic ions in Sn_0.90(Mn_0.05, Co_0.05)O₂ is investigated. The band structure model has been used to explain the strong ferrimagnetic interaction observed and the mechanism that stabilizes this state is proposed.     

Observation of Various and Spontaneous Magnetic Skyrmionic Bubbles at Room Temperature in a Frustrated Kagome Magnet with Uniaxial Magnetic Anisotropy

The quest for materials hosting topologically protected skyrmionic spin textures continues to be fueled by the promise of novel devices. Although many materials have demonstrated the existence of such spin textures, major challenges remain to be addressed before devices based on magnetic skyrmions can be realized. For example, being able to create and manipulate skyrmionic spin textures at room temperature is of great importance for further technological applications because they can adapt to various external stimuli acting as information carriers in spintronic devices. Here, the first observation of skyrmionic magnetic bubbles with variable topological spin textures formed at room temperature in a frustrated kagome Fe₃Sn₂ magnet with uniaxial magnetic anisotropy is reported. The magnetization dynamics are investigated using in situ Lorentz transmission electron microscopy, revealing that the transformation between different magnetic bubbles and domains is via the motion of Bloch lines driven by an applied external magnetic field. These results demonstrate that Fe₃Sn₂ facilitates a unique magnetic control of topological spin textures at room temperature, making it a promising candidate for further skyrmion‐based spintronic devices.     

Zero‐Field Nernst Effect in a Ferromagnetic Kagome‐Lattice Weyl‐Semimetal Co3Sn2S2

The discovery of magnetic topological semimetals has recently attracted significant attention in the field of topology and thermoelectrics. In a thermoelectric device based on the Nernst geometry, an external magnet is required as an integral part. Reported is a zero‐field Nernst effect in a newly discovered hard‐ferromagnetic kagome‐lattice Weyl‐semimetal Co₃Sn₂S₂. A maximum Nernst thermopower of ≈3 µV K^?1 at 80 K in zero field is achieved in this magnetic Weyl‐semimetal. The results demonstrate the possibility of application of topological hard magnetic semimetals for low‐power thermoelectric devices based on the Nernst effect and are thus valuable for the comprehensive understanding of transport properties in this class of materials.     

Magnetic studies of Sn2+–Sn4+-substituted barium hexaferrites synthesized by mechanical alloying

The effect of Sn²⁺–Sn⁴⁺ mixture on magnetic properties of BaM has been studied by Mössbauer spectroscopy and vibrating sample magnetometry. The results show that the magnetization reached a maximum for x=0.2 and then diminished. Mössbauer spectra showed that Sn²⁺–Sn⁴⁺ ions preferentially occupy 2b and 4f₂ sites, followed by 4f₁ and 2a sites; whilst the 12k was the least affected by the substitution. The preference for the 4f₂ and 4f₁ sites is responsible for the increase in the magnetization at low substitutions, due to their spin down configuration. At x≥0.3 values, a steep drop of both M_s and M_r was recorded, which might be due to the appearance of small amounts of tin oxide (SnO₂) as a secondary phase. A large variation of the intrinsic coercivity, H_ci, (4.8 to 0.909 kOe) was obtained as a function of the substitution. The rapid decrease of H_ci has its origin in the preference of Sn²⁺–Sn⁴ ions for the 2b and 4f₂ sites.     

Growth of diffusion layers at liquid Al–solid Cu interface under uniform and gradient high magnetic field conditions

The effect of high magnetic fields on interfacial reactive diffusion in liquid/solid (Al/Cu) couples was experimentally investigated at a temperature of 973 K. Regardless of any magnetic field, compound layers consisting of the δ, ξ₂, η₂ and θ phases were produced at the interface. The magnetic flux density, B, exerted a non-monotonic influence on the growth of the diffusion layers. Moreover, the mean thickness of the diffusion layers (parallel to B) was found to be always greater than that of the diffusion layers (perpendicular to B) under the applied magnetic fields. These phenomena should be attributed to the effects of two types of the Lorentz force under a uniform high magnetic field on diffusion behavior. In addition, the growth of intermetallic phases could be retarded by a magnetic field gradient due to the magnetic force in the axial direction.     

In situ study on growth behavior of Cu6Sn5 during solidification with an applied DC in RE-doped Sn–Cu solder alloys

The growth behavior of Cu₆Sn₅ intermetallic compounds in rare earth (RE)-doped Sn–Cu solder alloys with an applied direct current (DC) has been in situ investigated using synchrotron radiation imaging technology. The morphological evolutions of Cu₆Sn₅ with various shapes of I-like, Y-like and bird-like are directly observed. After doping RE, the number of I-like and bird-like Cu₆Sn₅ is decreased, but the number of Y-like Cu₆Sn₅ is increased. The morphologies of Cu₆Sn₅ are more uniform and the mean lengths of Cu₆Sn₅ of different shapes are reduced in RE-doped alloys compared with that in RE-free alloys, which is attributed to the adsorption effect of RE. The growth orientation of Y-like Cu₆Sn₅ is changed after La is doped. Additionally, with an applied DC, the nucleation rate of Cu₆Sn₅ is increased and the growth rate is markedly enhanced resulting in the refinement of Cu₆Sn₅. Furthermore, the mechanisms of refinement caused by RE and DC are specifically discussed.     

Superconducting and normal state properties of dilute alloys of LaSn3 containing Nd impurities

The results of an investigation of the superconducting and normal state physical properties of (LaNd)Sn₃ alloys are reported. Superconducting state data are presented describing the depression of the superconducting transition temperature T _cwith Nd impurity concentration, the reduction of the reduced jump in heat capacity C/C ₀ with decreasing reduced superconducting transition temperature T _c/T_c0, and the pressure dependence of T _c. Normal state data for the temperature dependences of the magnetic susceptibility and heat capacity demonstrate the importance of crystalline electric field effects in the physical behavior of (LaNd)Sn₃ alloys and indicate that Nd interimpurity magnetic interactions and possibly a small amount of Nd-Sn antisite disorder are manifested in the experimental results. Theories based on an isotropic exchange depairing model are unable to give a satisfactory account of all of the experimental data, suggesting that the physical properties of(LaNd)Sn₃ alloys may be modified by processes involving the orbital exchange scattering of host conduction electrons by the Nd impurities.Supported by the U.S. Department of Energy under Contract No. Ey-76-S-03-0034-PA227-3.Fellow of the Consejo Nacional de Investigaciones, Cientificas y Tecnicas, de la Republica Argentina; leave from Centro Atomico Bariloche, Bariloche, Argentina.     

Comparative analysis of crystal field effects and optical spectroscopy of six-coordinated Mn ion in the Y2Ti2O7 and Y2Sn2O7 pyrochlores

The electronic energy levels of the six-coordinated Mn⁴⁺ ion in the pyrochlores Y₂B₂O₇ (B = Sn⁴⁺, Ti⁴⁺) have been computed using the exchange charge model of crystal field theory. The calculated Mn⁴⁺ energy levels and their trigonal splitting are in good agreement with the experimental spectra. The calculated crystal field parameters show that the higher crystal field strength in Y₂Sn₂O₇ arises from an increased orbital overlap effect between the Mn⁴⁺ ion and the nearest oxygen ions, which are located at the 48f crystallographic position of the pyrochlore lattice. This increased overlap in Y₂Sn₂O₇ occurs despite the fact that the Mn⁴⁺-O²⁻ bond distance in Y₂Sn₂O₇ is longer than in Y₂Ti₂O₇ and is attributed to a lack of hybridization (covalent bonding) between the filled 2p orbital of oxygen ion occupying the 48f site of the pyrochlore lattice and the filled Sn⁴⁺ 4d¹⁰ orbital. The low temperature emission spectrum of Mn⁴⁺ activated Y₂Sn₂O₇ is analyzed in terms of a weak zero phonon line (R-line) with accompanying vibrational side bands.     

Interfacial reaction and elemental redistribution in Sn3.0Ag0.5Cu-xPd/immersion Au/electroless Ni solder joints after aging

Sn3.0Ag0.5Cu solder doped with 0, 100, and 500 ppm Pd was reflowed with electroless Ni/immersion Au substrate. As Pd concentration increased in the solder, formation and growth of (Cu,Ni)₆Sn₅ were suppressed. After thermal aging, Cu₄Ni₂Sn₅ and Cu₅NiSn₅ were observed at interface of Sn3.0Ag0.5Cu-xPd/Au/Ni systems. As compared to Cu₄Ni₂Sn₅, more Pd dissolved in Cu₅NiSn₅. In addition, Pd doping enhanced the growth of Cu₄Ni₂Sn₅ and slowed the formation of Cu₅NiSn₅, which would stabilize the intermetallic compound. Based on quantitative analysis by field emission electron probe microanalyzer, the correlation between Pd doping and elemental redistribution in solder joints was probed and discussed. This study described a possible mechanism of the formation of different intermetallic compounds in Pd-doped lead-free solder.     

Theory of Unusual Superconducting Phase Transitions in Heavy Fermion Metals at High Magnetic Fields

We present a non-perturbative theory of paramagnetically-driven superconducting (SC) phase transitions in heavy-fermion metals, which reliably determines their stable SC phases, treats properly the corresponding finite jumps of the order parameter, and can account for unusual features reported recently for this type of materials. It is found that for quasi-2D heavy-fermion metals, such as CeCoIn₅, at high magnetic fields oriented perpendicular to the highly conducting planes, the effect of the Fulde-Ferrel (FF) modulation is too weak to prevent a direct first-order phase transition from the normal to the uniform SC state. For 3D heavy-fermion metals, such as URu₂Si₂, the FF modulation stabilizes, under a decreasing magnetic field, a non-uniform SC state via a second-order phase transition from the normal state. However, at a slightly lower field the modulated phase becomes unstable, transforming to a uniform SC state via a first-order transition.