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We have explored the crystal structure and magnetic properties of two intermetallic solid solutions of the IrIn3 structure type. Although Fe0.95Co0.05Ga3 and Fe0.975Ni0.025Ga3 are isomorphous and possess exactly the same concentration of valence electrons, they display noticeable differences in their crystal structure associated with a different nature of the Fe Co and Fe Ni dumbbells. The former contains an odd number of electrons compared to an even number of the latter dumbbell. Responding to localized spins of the Fe Co dumbbells, the 69Ga NQR relaxation rate in Fe0.95Co0.05Ga3 is governed by temperature independent spin-lattice relaxation typical for diluted paramagnetic centers at low temperatures. In Fe0.975Ni0.025Ga3 with zero magnetic moment of the dumbbells the 69Ga spin-lattice relaxation rate is strongly reduced and in-gap states in the energy gap show up as a broad maximum near 70 K.

We report the electronic properties of the Yb3Rh4Sn13-type single crystalline Ca3Rh4Sn13 by means of the electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, as well as 119Sn nuclear magnetic resonance (NMR) measurements. The negative sign of the Hall coefficient and Seebeck coefficient at low temperatures suggests that the n-type carriers dominate the electrical transport in Ca3Rh4Sn13, in contrast to the observations in Sr3Rh4Sn13 which has a p-type conduction. Such a finding indicates a significant difference in the electronic features between these two stannides. Furthermore, we analyzed the temperature-dependent 119Sn NMR spin-lattice relaxation rate for Ca3Rh4Sn13, (Sr0.7Ca0.3)3Rh4Sn13, and Sr3Rh4Sn13 to examine the change of the electronic Fermi-level density of states (DOS) in (Sr1-xCax)3Rh4Sn13. It indicates that the Sn 5s partial Fermi-level DOS enhances with increasing the Ca content, being consistent with the trend of the superconducting temperature. Since the total Fermi-level DOS usually obeys the same trend of the partial Fermi-level DOS, the NMR analysis provides microscopic evidence for the correlation between the electronic DOS and superconductivity of the (Sr1-xCax)3Rh4Sn13 system.

Electrical and thermal transport properties of the Heusler-type alloys, Ru2VAl1−xGax (x = 0.0–1.0) were studied by means of the electrical resistivity, Seebeck coefficient, and thermal conductivity measurements. All studied compounds show weak metallic characteristics with a low residual resistivity ratio. In addition, the Ru2VAl1−xGax alloys with x ≤ 0.75 show an n-type thermoelectric conduction from 10 to 300 K, while Ru2VGa displays p-type conduction. The estimated Fermi energy of these materials is higher than 0.5 eV, endorsing their metallic character. From the thermal conductivity study, we noticed that low-temperature thermal conductivity decreases with increasing Ga content for x ≤ 0.5 and then increases with further Ga substitution. This observation is essentially due to the change in the phonon scattering processes as a result of the substitution of heavier Ga atoms into the Al sites of Ru2VAl. It is important that an enhanced thermoelectric figure of merit ZT was found in Ru2VAl0.25Ga0.75, about seven times higher than that in Ru2VAl.

In this study, a Co-thin film was deposited on the van der Waals compound of FePS 3 for the investigation of interfacial magnetic coupling, which is crucial to the application in spintronic devices. As characterized by atomic force microscopy, the exfoliated FePS 3 surface was composed of defects within ± 1 monolayer height. The Co thin film covered the FePS 3 substrate uniformly with a roughness within ± 0.5 nm. The 2 nm-Pd/7 nm-Co/FePS 3 exhibited isotropic magnetism in the surface plane and the magnetic coercivity drastically decreased by more than 50% when the temperature was elevated from 85 K to 110–120 K, which is nearly the Neel temperature of FePS 3 . This observation indicates the interfacial magnetic coupling between Co and FePS 3 . The Co/FePS 3 magnetic coupling is robust even after annealing up to 200 °C. Furthermore, the measurement of X -ray magnetic circular dichroism confirmed the presence of non-compensated Fe moment along the in-plane direction is parallel to the Co magnetization direction. The net Fe-moment is supposed to play an essential role in mediating the magnetic coupling between the in-plane ferromagnetic Co and the perpendicular antiferromagnetic FePS 3 .

We report a study of the thermoelectric properties of the two series of Ru2NbGa Heusler-type alloys by attempting chemical substitutions; (i) making the off-stoichiometry between Ru and Nb in Ru2-xNb1+xGa (x = 0.00, ±0.05, and 0.10) and (ii) doping the sp-elements M = Sn, In, and Ge onto the Ga sites in Ru2NbGa1-xMx (x = 0.05, 0.10, 0.20). All the investigated alloys show predominantly a semiconducting-like feature in the temperature-dependent electrical resistivity and the Seebeck coefficient measurements. Interestingly, the sample with x = −0.05 in the off-stoichiometry Ru2-xNb1+xGa series exhibits a substantial decrease in electrical resistivity as compared to the pristine Ru2NbGa sample and demonstrates metallic behavior at low temperatures. Besides, the Seebeck coefficient for the x = 0.10 alloy displays a positive sign in the temperature range under investigation, indicating that the hole-type carriers dominate the thermoelectric transport. This finding is in contrast to other compositions that show a negative sign in the Seebeck coefficient, suggesting that a significant modification of the electronic structure in the Ru1.90Nb1.10Ga alloy. Temperature-dependent thermal conductivity reveals the behavior of the excitation of phonon modes with temperature and indicates a dominant lattice phonons heat conduction in all alloys. Moreover, the thermal conductivity was found to be little affected by the chemical substitution, which is mainly caused by the crystallographic disorders through the different atomic mass and radius of the host and the substituent. The thermoelectric performances, i.e., the power factor (PF) and figure of merit (ZT), were calculated. We found an enhancement in the PF and ZT values in Ru2NbGa0.90Sn0.10, Ru2NbGa0.90Ge0.10, and Ru2NbGa0.95In0.05 alloys as compared to the parent compound of Ru2NbGa.

Investigation on temperature-dependent electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) of intermetallic Fe1−xCoxGa3 (0.005 ⩽ x ⩽ 0.5) compounds are carried out to probe their thermoelectric performance. From resistivity study, it is observed that increase in number of valence electrons introduced by Co doping leads to a change from semiconducting to metallic behavior, which occurs between x = 0.05 and 0.125. The characteristics of the Seebeck coefficient show a substantial decrease with the Co doping, due to the modifications in the band gap and the Fermi-level density of states. Analyses of thermal conductivity of the Co doped FeGa3 compounds reveal that thermal transport is essentially due to the lattice phonons. It is also noticed that the low-temperature peak in the lattice thermal conductivity of these compounds is reduced significantly with the increase in Co content, attributing to the enhanced scattering of phonons by point-defects. The value of the figure-of-merit, ZT = (S2/ρκ)T, is estimated for all compounds, and the maximum room-temperature ZT value of about 0.02 was achieved for Fe0.95Co0.05Ga3, and increased further with temperature to the value of about ∼0.05 at 400 K.

We report the results of aluminum substitution on the temperature-dependent electrical resistivity, Seebeck coefficient, as well as thermal conductivity of SrSi 2− x Al x alloys with 0 ≤ x ≤ 0.20. It is found that the substitution of Al onto the Si sites of SrSi 2 causes a significant decrease in the electrical resistivity and the Seebeck coefficient. The observations are associated with the downward shift of the Fermi level, due to hole-doping via Al substitution within a rigid-band scenario. The low-temperature thermal conductivity decreases markedly with increasing Al content. Analysis of the lattice thermal conductivity from the contribution of various thermal scattering mechanisms reveals that the reduction in the lattice thermal conductivity mainly arises from the grain-boundary and point-defect scattering of the phonons through chemical substitution.

Unlimited solid solution Fe1� xCoxGa3 was prepared from Ga flux. Its crystal structure was refined for Fe0.5Co0.5Ga3 (P42/mnm, a¼6.2436(9), c ¼ 6.4654(13), Z¼ 4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and 69,71 Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe–Fe and Co–Co dumbbells are preferred to the Fe–Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x40. The solid solution is metallic for x40.025. The study of the nuclear spin–lattice relaxation shows that the rate of the relaxation, 1/T1, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N 2 (EF).

a b s t r a c t We report the results of a 23 Na nuclear magnetic resonance (NMR) study on Na3Cu2SbO6 at temperatures between 4 and 300 K. This material has been a subject of current interest due to indications of spin gap behavior. The temperature-dependent NMR shift exhibits a character of low-dimensional magnetism with a broad maximum at Tmax � 95 K. While the NMR shift data can be fitted well to both antiferromagnetic–antiferromagnetic (AF–AF) and antiferromagnetic–ferromagnetic (AF–F) alternating chain models, the former yields a spin gap of 62 K which is too small as compared to the value obtained from the neutron scattering measurement. On the other hand, a spin gap of about 112 K based on the AF–F alternating chain scenario is quite consistent with the reported value. In addition, the employment of the AF–F alternating chain picture to analyze the spin-lattice relaxation rate reveals a gap size of 105 K, in good agreement with the 8.9 meV peak observed in the inelastic neutron scattering experiment. With this accordance, we point out that the AF–F alternating chain picture is more appropriate for the

We report the results of yttrium substitution on the electrical resistivity (r), the thermal conductivity (k), as well as the Seebeck coefficient (S) of the Sr1� xYxAl2Si2 alloys with 0 � x � 0.20. Both r(T) and S(T) data suggest that SrAl2Si2 is a semimetallic, low charge carrier density system with a pseudogap at the Fermi level density of states (DOS). Upon substituting Y onto the Sr sites, the electrical resistivity and the absolute value of the Seebeck coefficient decrease significantly. Such an observation can be associated with the modification of the electronic band structure due to electron doping via Y substitution. Analysis of the thermal conductivity reveals the contribution of various thermal scattering mechanisms through chemical substitution. Theoretical studies with density functional theory are also employed to investigate the electronic band structure of Sr1�x YxAl2Si2. It is revealed that SrAl2Si2 possesses a shallow DOS at the Fermi level with both n-type and p-type charge carriers. Upon Y substitution a shift in the Femi level occurs such that the Sr1�x YxAl2Si2 system becomes more metallic with increasing x, being consistent with the experimental findings.

article i nfo Available online 1 April 2011 Measurements of the electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) on the rare earth ternary intermetallic YMn4Al8 has been performed in the temperature range 10-300 K to investigate the electronic structure and the possible existence of pseudogap. YMn4Al8, with linear chains of Mn atoms, is an itinerant electron magnet that has a narrow pseudogap in the spin excitation spectrum. For comparison, the nonmagnetic counterpart YCu4Al8 has also been studied. It is found that the replacement of Cu for Mn leads to a dramatic increase in the electrical conductivity, indicating an increased metallic nature of YCu4Al8. The evident difference in the magnitude of the Seebeck coefficient between YMn4Al8 and YCu4Al8 as well as the sign reversal of S(T) in YCu4Al8 suggest that the Fermi level in YMn4Al8 is located within a rapidly varying density of states (DOS)/pseudogap and a significant change in temperature dependent DOS is taking place. A detailed analysis of the thermal conductivity by separating lattice and electronic contribution and the comparison with the electrical resistivity indicates a more ordered and increased metallic state for YCu4Al8 than that of YMn4Al8.

Normal state electrical and thermal properties, including electrical resistivity ( ρ ), Seebeck coefficient ( S ), and thermal conductivity ( κ ) of the CaAl x Si 2− x ( x =0.9–1.2) system were investigated. It is found that the electrical resistivity and Seebeck coefficient exhibit a typical metallic character throughout the temperature range investigated, and the metallicity of this series is enhanced with increase in Al/Si ratio. On the other hand, the thermal conductivity shows a weak temperature variation at low temperatures, whereas κ follows a T 2 -dependence for T >150 K. Analysis of the electronic thermal resistivity based on Klemen’s model reveals that the scattering of electrons from the defects and static imperfections becomes dominant as the temperature approaches T c . These results are discussed in the light of simultaneous existence of various crystal structures and development of ultra-soft phonon mode recently observed in the CaAlSi system.

A series of Ni 2 MnGa 1− x Al x ( x = 0, 0.03, 0.05, 0.10, 0.15 and 0.20) alloys are studied by means of electrical resistivity, ρ ( T ), Seebeck coefficient, S ( T ), thermal conductivity, κ ( T ), as well as specific heat measurements. It is observed that the martensitic transition temperature show a significant but complex variation for the low level of partial Al substitution with respect to Ga whereas magnetic ordering temperature is little affected. However, upon increasing Al content ( x ≥ 0.10), a drastic suppression of the martensitic transition along with a gradual broadening/suppression of the magnetic ordering take place. Such observations are in sharp contrast to the general expectation for the nonmagnetic and isoelectronic Al substitution with respect to Ga. X-ray diffraction studies revealed that increase in Al substitution leads to the formation of B 2 phase and which plays an important role on the martensitic and magnetic transition characteristics and physical properties of Ni 2 MnGa 1− x Al x alloys.

The effects of Ge partial substitution onto Si site of Er 5 Si 4 alloy were investigated by means of thermal and electrical transport measurements. Temperature-dependent electrical resistivity ( ρ ), Seebeck coefficient ( S ), and thermal conductivity ( κ ) measurements from 7 to 300 K were performed on a series of Er 5 Si 4− x Ge x alloys with x varying from 0 to 2. Noticeable anomalies were observed at the magnetic phase transition in Er 5 Si 4 alloy in these transport measurements. It was also found that the resistivity of Er 5 Si 4− x Ge x alloys gradually increases and the Curie temperature T C decreases upon replacing Si with Ge. No sign of anomalous feature was detected in Er 5 Si 2 Ge 2 , indicating that the magnetic phase transition may be suppressed at this substitution level.

Temperature can induce some free carriers in semiconducting carbon nanotubes (SCNs). Such carriers would exhibit the temperature-dependent electronic excitations. The dielectric function e , which represents the intrinsic excitation properties, is calculated with the random-phase approximation (RPA). The screened excitation spectra include both L = 0 intraband e–h excitations and L = 1 damped interband plasmon. Such electronic excitations are very effectively deexcitation channels. When electrons are excited from valence bands to conduction bands by the external fields, they could further decay by the e–e Coulomb interactions. Time-resolved carrier deexcitations processes in SCNs have been investigated by means of pump-probe experiments. This is the first theoretical work on the electron decay rate due to the e–e Coulomb interactions. The Fermi Golden rule, which includes the screened e–e interactions , is used to calculate the decay rate. 1/ τ is very sensitive to change in state energy or wave vector. The L = 0 intraband e–h deexcitations mainly occur in the low-energy states, and the band-edge state has the largest decay rate. The high-energy state might be deexcited by the L = 1 mode. The calculated results could essentially explain the experimental measurements from the time-resolved photoemission spectroscopy.

The quantum-size features of finite carbon nanotubes would induce interesting electronic and optical properties. The discrete electronic states in the presence of the static electric field (E) are calculated from the tight-binding model with the curvature effects. Electronic properties (symmetry of electronic states, energy spacing; state degeneracy) are significantly affected by the magnitude and the direction (α) of E, and the geometric structure (radius, length; chirality). E can make the complete energy-gap modulation. The optical excitation spectra exhibit rich absorption peaks, which directly reflect the characteristics of electronic properties. The absorption frequency, the number of absorption peaks, and the spectral intensity are very sensitive to the change in E. There are more absorption peaks when E is oriented closer to the cross-section plane. The optical measurements could be used to verify the predicted absorption spectra and electronic properties.

We use the sp 3 tight-binding model to calculate electronic structures of single-walled carbon nanotubes. All the n and a electrons would take part in charge screening. As a result of the cylindrical symmetry, the momentum (q) and angular momentum transfer (L) are conserved in the electron-electron Coulomb interactions. The static dielectric function e (q,L), which determines the charge screening ability, is evaluated from the random-phase approximation. e of L = 1 at long wavelength limit (q → 0) is very important in understanding the dielectric screening in the presence of a uniform transverse electric field E ⊥ . e (q = 0,L = 1) hardly depends on the chiral angle, and the dependence on the nanotube radius is weak. It quickly grows as the Fermi level increases, that is, the screening response is largely enhanced by the increasing free carriers.

Electrical and magnetic properties of CeCuGe were investigated through electrical resistivity, thermal conductivity and magnetization measurements in the temperature range 2–300 K. Magnetization measurements indicate a paramagnetic to ferromagnetic transition at T=10 K, in agreement with previous work. There are two distinct paramagnetic regimes: At high-T the magnetic moment per cerium is 2.50 μB, nearly equal to the expected 2.54 μB for Ce3+, while at low-T the effective moment decreases to 2.20 μB per cerium. This decrease is attributed to crystalline electric field effects. In the ferromagnetic region, the hysteresis curve indicates a rather small anisotropy (Hc less than 20 Oe). There is also very little remanence (the ratio of the remanence to the technical saturation magnetization is about 0.05), implying that this material is magnetically quite soft, with a very small magnetocrystalline anisotropy, contrary to what was reported in a previous investigation. In the temperature regime 10–30 K the resistivity obeys a T2-behavior, consistent with the appearance of spin fluctuations above the ferromagnetic transition. In the same temperature regime, the thermo-power exhibits a linear rise in addition to a T2 term, anomalous behavior which we also attribute tentatively to the development of spin fluctuations.

The transport properties including electrical resistivity ( ρ ), thermal conductivity ( κ ), as well as Seebeck coefficient (S) of intermetallic FeGa3 have been measured as a function of temperature between 10 and 300 K. The electrical resistivity exhibits metallic behavior in the temperature range we investigated. The thermal conductivity is approximately 6 W/m K at room temperature, and is mainly governed by the lattice thermal conductivity. The observed Seebeck coefficient is positive, indicating p-type carriers dominating the thermoelectric transport for FeGa3. In addition, the Fermi level of 0.14 eV measured from the top of valence band was estimated. These observations are in contrast with the reported semiconducting behavior for this compound, presumably attributed to the off-stoichiometric effect on the electronic band structure of FeGa3.

In order to access the spin glass-like feature in the CoSi 1-x Al x alloys, we measured the DC magnetization under zero-field-cooled (ZFC) and field-cooled (FC) procedures for CoSi 0.85 Al 0.15 and CoSi 0.70 Al 0.30 with various external magnetic fields. It has been found that the magnetic susceptibility and the irreversibility between ZFC and FC measurements in both compounds are very sensitive to the applied field. We associated the formation of the spin glass state with the Si/Al disorder in these materials.

We report the investigations of specific heat, thermal conductivity and thermoelectric power on the intermetallic Lu5Rh4Si10 at temperatures above the superconducting transition Tc∼3.9 K. All measured results consistently show anomalous peaks at its charge density wave (CDW) transition TP∼147 K. The observed peaks in the specific heat and thermal conductivity are significantly large, in contrast to conventional CDW systems. It suggests that possibly strong interchain interactions manifest the CDW transition in this material.

We report the transport properties, including electrical resistivity ( ρ ) and Seebeck coefficient ( S ) of Ge-substituted MnSi 1− x Ge x (with x =0, 0.02, 0.05, and 0.10) alloys as a function of temperature between 10 and 300 K. It was found that the partial substitution of Ge at Si site has a surprisingly weak effect on the ferromagnetic transition temperature T C in MnSi, indicating that the negative chemical pressure produced by the substitution of larger ion Ge in place of Si is unable to significantly influence the magnetic ordering. In addition, the temperature-dependent Seebeck coefficient shows similar behaviour for theses alloys, which suggests that the electronic density of states (DOS) of MnSi near the Fermi level is essentially unaffected by Ge substitution for Si.

Spin gap characteristics of the Zn-substituted quasi-one-dimensional (1D) compounds BaCu 2− x Zn x V 2 O 8 ( x =0, 0.1, 0.2, and 0.5) have been investigated by means of the 51 V NMR measurements. For all studied compositions, two 51 V NMR lines which are associated with two vanadium crystallographic sites have been resolved. Within the present doping level, the temperature-dependent NMR shift of each individual site exhibits a character of spin gap. While the deduced spin gap remains almost unchanged, the entire curve of the NMR shift substantially decreases for the high Zn concentration. Such an observation is interpreted as the reduction of the transferred hyperfine field from Cu 2+ , due to the creation of spin vacancies along the spin chains.

We report the results of 27 Al NMR Knight shift measurement on FeSi 1− x Al x ( x =0.02 and 0.05) as related to the influence of Al substitution on the magnetic properties and energy gap features of FeSi. For both compositions, the temperature-dependent 27 Al NMR Knight shifts exhibit activation-type behavior with the broad maximum at around 400 K. The observed data can be well reproduced by using a model band structure with two narrow peaks in the density of states separated by a small energy gap. The deduced gap was found to be insensitive to the Al content, indicative of little modification on the band structure of FeSi with addition of itinerant carriers. However, the absolute value of Knight shift increases with Al concentration, revealing an enhancement of the Pauli-type spin susceptibility via Al substitution.