Spin-disorder resistivity in the Cu2Mn(Al1−xSnx) heusler alloys

Electrical resistivity measurements have been performed on the Cu₂Mn(Al_1?xSn_x) Heusler alloys, where x = 0; 0.05; 0.10; 0.15, in the temperature range of 4–800 K. The experimental curves clearly show the importance of the ferromagnetic character on the resistivities of the alloys. The results obtained are in agreement with an interpretation in terms of a spin-disorder model.     

Spin-disorder resistivity in Ni2Mn(Sn1−xInx) heusler alloys

Electrical resistivity measurements have been performed on Ni₂Mn(Sn_1?xIn_x) Heusler alloys, where x = 0, 0.02, 0.05, 0.10 and 0.15, in the temperature range of 4–300 K. The experimental data clearly show the existence of two distinct kinds of resistivity behaviour, both described by an aTⁿ law, for 7 ? T ? 20 K. Between 170 and 300 K the data are well described by an AT + BT² phenomenological fit, and the results obtained are in good agreement with an interpretation based on electron-phonon and spin-disorder scattering.     

Die Temperaturabhängigkeit der magnetischen Jordan-Nachwirkung von Nickel

The magnetic after effect of pure polycristalline nickel and of a single crystal was measured between ?196 and +340 °C by a Förster second harmonic magnetometer. The viscosity constantS _v is shown to be proportional toB(T)·H_c(T) with an increasing functionB(T) for specimens of different magnetic hardness. The temperature dependence S_v(T) atH _c is rather complex in comparison to the simpleT- or √T-behaviour of former theoretical models. The latter is observed only forT??100 °C, whileS _v is nearly independent ofT between ?100 and +300 °C, and drops abruptly to zero forT?300 °C.     

Electrical resistivities of the intermetallic compounds NpRu2 and NpOs2

The electrical resistivities of the cubic intermetallic compounds NpRu₂ and NpOs₂ have been measured in the temperature range 1.5–300° K. The resistivity of NpRu₂ varies as T² up to 13° K. This behavior is in agreement with the predictions of the localized-spin-fluctuation model. The resistivity-temperature curve of NpOs₂ has the characteristics of a material that orders magnetically. The ordering temperature T_C = (7.4±0.5)°K was obtained from analysis of the data. The difference between the magnetic properties of NpRu₂ and NpOs₂ is discussed in terms of the variation in the actinide-actinide interatomic distance in these compounds.     

The electronic properties of chromium borides

Measurements of magnetic susceptibility between 300 and 100°K and of resistivity between 300 and 4.2°K are reported for the five intermediate compounds Cr₂B, Cr₃B₃, CrB, Cr₃B₄ and CrB₂. With the exception of CrB₂ (antiferromagnetic T_N = 88°K) all the compounds were found to be weakly temperature dependent paramagnets. Large, orbital contributions to the susceptibility are proposed for Cr₂B and Cr₅B₃. It is suggested that with the formation of discrete boron networks and the associated change in band structure in the higher borides this contribution diminishes very rapidly. At low temperatures Cr₂B₁ CrB and CrB₂ were all found to have a prominent T² behaviour in ρ(T). At high temperatures the resistivities of CrB and CrB₂ were found to vary linearly with temperature, the resistivity of Cr₂B on the other hand seemed to follow a T(1 ? BT²) law.     

Manifestation of quantum statistics in vibrational dynamics of poly(ethylene) crystals

The temperature dependences of the transverse expansion ?_⊥(T) and the longitudinal contraction ?_‖(T) (with respect to the axes of chain molecules) in large-sized poly(ethylene) (PE) crystal grains (100×60×60 nm) are measured using x-ray diffraction in the temperature range 5–380 K. The temperature dependence of the elongation of the molecular skeleton ?_C(T) is obtained by Raman spectroscopy. It is found that the dependences ?_⊥(T), ?_‖(T), and ?_C(T) exhibit a similar specific nonlinear behavior. Analysis of these dependences indicates that the nonlinearity is associated with the quantum statistics of transverse vibrations. The energies and amplitudes of zero-point (at T=0) transverse (torsional and bending) vibrations and the relevant zero-point components ?_‖(0) and ?_C(0) are estimated. It is revealed that the zero-point components make a considerable contribution to the dynamics of the PE crystal up to the melting temperature (～400 K).     

Heat capacity and thermodynamic properties of HoMnO<Subscript>3</Subscript> in the range of 364–1046 K

The temperature dependence of the molar heat capacity of HoMnO₃ has been measured by differential scanning calorimetry. The experimental data have been used to calculate the thermodynamic properties of the oxide compound (changes in the enthalpy H°(T)–H°(364 K), entropy S°(T)–S°(364 K), and reduced Gibbs energy Φ°(T)). The data on the heat capacity of HoMnO₃ have been generalized in the range of 40–1000 K.     

Structure-mediated transition in the behavior of elastic and inelastic properties of beach tree bio-carbon

Microstructural characteristics and amplitude dependences of the Young modulus E and of internal friction (logarithmic decrement δ) of bio-carbon matrices prepared from beech tree wood at different carbonization temperatures T _carb ranging from 600 to 1600°C have been studied. The dependences E(T _carb) and δ(T _carb) thus obtained revealed two linear regions of increase of the Young modulus and of decrease of the decrement with increasing carbonization temperature, namely, ΔE ～ AΔT _carb and Δδ ～ BΔT _carb, with A ≈ 13.4 MPa/K and B ≈ ?2.2 × 10^?6 K^?1 for T _carb < 1000°C and A ≈ 2.5 MPa/K and B ≈ ?3.0 × 10^?7 K^?1 for T _carb > 1000°C. The transition observed in the behavior of E(T _carb) and δ(T _carb) at T _carb = 900–1000°C can be assigned to a change of sample microstructure, more specifically, a change in the ratio of the fractions of the amorphous matrix and of the nanocrystalline phase. For T _carb < 1000°C, the elastic properties are governed primarily by the amorphous matrix, whereas for T _carb > 1000°C the nanocrystalline phase plays the dominant part. The structurally induced transition in the behavior of the elastic and microplastic characteristics at a temperature close to 1000°C correlates with the variation of the physical properties, such as electrical conductivity, thermal conductivity, and thermopower, reported in the literature.     

Electron-phonon scattering in potassium at high magnetic fields

We have measured the temperature dependence of both the zero-field resistivity and the transverse magnetoresistance of polycrystalline potassium wires (?(300 K)/?(4.2 K)=140 to 6000) in fieldsH?35 kG and at temperaturesT?4.2 K. Our principal findings are: 1) The presence of a large magnetic fieldH=35 kG does not alter the temperature dependence of ? from that observed atH=0; below 4.2 K theT-dependent part of the resistivities,_?T (H=0) and_?T (H=35 kG), fit well to the function exp (?Θ*/T) with the same Θ*=23K. 2) Deviations from Matthiessen's rule are significantly reduced in a strong field so that the magnitude of_?T (H=0) approaches that of_?T (H=35 kG) as sample purity decreases. 3) The slope of the high-field linear magnetoresistance increases slightly (?8%) from 1.5 K to 4.2 K. We attribute the exponential temperature dependence of_?T (H) to the freezing out of electron-phonon umklapp processes as has been shown for the zero-field resistivity. The reduction in deviations from Matthiessen's rule at high fields can be understood within semiclassical theory, but the latter cannot explain the failure of_?T (H) to saturate at high fields. A proposal by Young that electron-phonon umklapp scattering may contribute aT-dependent high-field linear magnetoresistance in potassium is considered.     

Magnetic properties of Zr(Cr1−xCox)2 alloys and their hydrides

Magnetic properties of Zr(Cr_1?xCo_x)₂ alloys, with 0 ? x ? 0.75, and their hydrides were determined over the temperature range 4 to 275 K. All systems were paramagnetic. The susceptibility (?) is significantly enhanced both by increase of the Co content and by hydrogenation in all cases except cubic ZrCr₂, for which ? is virtually unchanged by hydrogenation. The rise in ? is ascribed to electron transfer from Co to Cr and to H. This transfer increases the local density of states for Co at the Fermi energy. The temperature dependence of the susceptibility can be represented by an equation of the form ? = ?₀ + C/(T ? θ), indicating Pauli and Curie-Weiss contributions to ?. The contributions are attributed to the ZrCr₂ matrix and the solute Co atoms, respectively. The Co atoms on Zr sites are weakly coupled antiferromagnetically. Pressure-composition isotherms for the ZrCrCo-H₂ system are given at 80, 120 and 165°C. At 80°C this alloy hydrogenates to the composition ZrCoCrH_3.25 at a pressure of 50 atm.     

Zur Widerstandsanomalie von Legierungen bei tiefen Temperaturen

Dilute alloys of Cu-Fe, Au-Fe, Zn-Mn, and Ag with V, Cr, Mn, Fe, Co are produced by simultaneous evaporation of both components on a substrate at 77 °K. By this method one succeeds in solving all systems, especially Cu alloys with high Fe concentration, which alloys normally show precipitations after cooling from the molten state. For these alloys we observe resistance minima up to 150 °K. Besides this, Cu-Fe shows a resistance maximum which depends on concentration. For Au-Fe and Ag-Mn we measure resistance anomalies which are even bigger for quenched films than for annealed films and bulk material. Apparently the lattice defects have an influence on the resistance anomaly. The increase of the resistance with decreasing temperature can be described by the functionρ _s /ρ _s0 =f(T/T _k ) for all systems. The result does not agree with the theories basing on Kondo's model. Here is tried an explanation by means of spin-orbit interaction. This interaction results in a temperature dependent cross-section for a molecule consisting of a magnetic impurity and a lattice defect.     

Giant quantum oscillations of the magnetothermoelectric coefficient in semimetallic Sb-Bi and Sb-As alloys

Quantum oscillations of the magnetothermoelectric coefficient α_ii(B) are investigated in semimetallic Sb-Bi and Sb-As alloys in stationary magnetic fields up to 15 T and at temperatures from 1.9 to 30 K. Quantum oscillations of α_ii(B) of a giant amplitude are observed when the longitudinal or transverse magnetic field is oriented along a binary C ₂ axis or a bisectory C ₁ axis and also when rotating the transverse magnetic field in angle ranges up to [+55°, ?55°] around them.     

High temperature EPR linewidths in MnO and MnS

EPR linewidths ΔH in MnO and MnS were studied at 300–1100°K. The remarkable constancy of _χT(ΔH) for T ? 3T_N follows from an extension of the Mori-Huber theories and delineates the region where critical-like behavior first becomes apparent as T approaches T_N.     

Note on the magnetic properties of amorphous rare-earth nickel alloys

The magnetic properties of several amorphous rare-earth nickel alloys close to 30 at% Ni have been studied in the temperature range 4.2–300 K. The Curie temperatures range from 2 K in Pr₆₉Ni₃₁. Alloys in which the rare-earth component has an orbital moment show large intrinsic coercive forces below T_c. These coercive forces vary considerably with temperature, the temperature dependence of the alloys Dy₆₉Ni₃₁ and Tb₆₉Ni₃₁ is satisfactorily described by means of an exponential law of the form H_c(_T) = H_c(0) exp(-αT).     

Quasiequilibrium treatment of the coverage of oxygen on tungsten at high temperature and low pressure

The quasiequilibrium treatment of heterogeneous reactions suggested by Batty and Stickney¹) and first order desorption kinetics are combined to formulate a model of the equilibrium coverage of oxygen on tungsten at high temperatures (1200 ? T ? 2500°K) and low oxygen partial pressures (10^?9 ? P_O2 ? 10^?5 Torr). The results are compared with existing data and the agreement is fairly good in view of the extreme simplicity of the theoretical model.     

Independence of spin and phonon resistivity in some kondo alloys

The temperatures of the resistivity minima (T_min) of several AlMn, AlCr, ThU, ZnMn and ZnCr alloys are calculated by using the empirical expressions for the phonon resistivities. The comparison between the calculated and observed T_min values seems to indicate the approximate additivity of spin and phonon resistivities in these alloys.     

Thermophysical study of structural phase transitions in Na<Subscript>0.95</Subscript>Li<Subscript>0.05</Subscript>NbO<Subscript>3</Subscript> solid solution

Temperature dependences of specific heat C_p(T) and coefficient of thermal expansion ;(T) for Na_0.95Li_0.05NbO₃ sodium-lithium niobate ceramic samples are investigated in the temperature range of 100–800 K. The C_p(T) and α(T) anomalies at T₃ = 310 ± 3 K, T₂ = 630 ± 8 K, and T₁ = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ? Q ? S(R) ? T2(S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition Q → R/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the C_p(T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed.     

Structural and magnetic studies of the alloy system GdInxAg1-x

The structural and magnetic studies below room temperature of the alloy system GdIn_xAg_1-x(0?x?1) are reported. It has been found that alloys with x?0.5 crystallize in CsCl type cubic structure, but the distortion of the unit cell starts for alloys with x#62;0.5 and for these alloys the unit cell becomes tetragonal. No phase change is evident from the low temperature (295-8 K) structural studies. However, a break appears in the X^-1_m vs. T linear plot of each alloy of this system at a specific temperature (designated as break temperature T_B). The variation of T_B with x is similar to the variation of phase transition temperature with x reported for LaIn_xAg_1-x. Close agreement has been found in the values of effective magneton number (p), magnetic ordering [Néel (T_N) or Curie (T_C)] and paramagnetic Curie (θ_p) temperature for materials studied by us and earlier workers. The variation of magnetization with applied field strength (2.5-65)×10⁵ Am^-1) at 4.2 K has also been reported for ferromagnetic of this system. It has been concluded that alloys with 0.4?x?0.6 are simple ferromagnets with parallel alignment of magnetic moment in the ground state. The angular arrangement of the magnetic moment starts appearing in the ground state for alloys with x?0.4 for x#62;0.6 and continues till x becomes closure to 0.17 or 0.84. The alloys with x=0.17 or x=0.84 have θ_p and T_C equal to zero and appear paramagnetic. Angular arrangement in spins again appear for alloys with x?0.17 or x#62;0.84, however all materials with 0?x?0.17 or 0.84?x?1 remain antiferromagnetic.     

High-temperature absorption coefficient of methane at 3.392μ

The spectral absorption coefficient of methane at 3.392μ has been measured in the temperature range 965 ?T, °K≤2710 behind incident and reflected shock waves. It is given by the relation P'=P'₀(T₀/T)ⁿ where P'₀=(1.34±0.58)x10²cm^-1atm^-1 at T₀=300°K and n=2.88±0.21. The empirically determined temperature exponent n may be approximately accounted for by a simplified theoretical analysis.