Specific Magnetic Susceptibility Research Articles

Electronic and magnetic investigation of thefilled skutterudite compound CeRu4Sb12

We synthesized the filled skutterudite CeRu4Sb12 insingle-crystal form using a molten-metal-flux technique with Sbflux. The specific heat and magnetic susceptibility ofCeRu4Sb12 are well described by a logarithmic divergence ora power law in temperature indicating non-Fermi-liquid behaviour atlow temperatures. The electrical resistivity is sample dependentwith some specimens exhibiting non-Fermi-liquid behaviour below T~5 K in which ρ∝Tn with n~1.4. Theapplication of magnetic fields up to H = 80 kOe does notsignificantly change the non-Fermi-liquid ground state.

Record of industrial pollution in polish ombrotrophic peat bogs

Peat contains mostly diamagnetic organic matter, which is a good collector of all kinds of atmospheric dusts and industrial pollution. Ombrotrophic peat bogs are built up above the ground water table, so deposition and accumulation of magnetic particles are not influenced by ground water and the deposited particles remain largely “in situ”. During this study, 6 Polish ombrotrophic peat bogs from different locations have been investigated. Peat cores of about 30–50 cm in depth were taken from every bog. The specific low-frequency magnetic susceptibility was measured along the peat profile in fresh, not dried sample. In most profiles the susceptibility below 10 cm was slightly negative, which is characteristic for clean organic material. Above a depth 8–10 cm the susceptibility starts to increase. Independently of the profile location, the increase is observed in all bogs and according to isotopic (C-14) dating it is connected with the post war industrialisation (1945–1955). The maximum of the magnetic deposition noticed as maximum susceptibility enhancement is observed in a depth of about 5 cm below the surface. In the south-western part of Poland the peat profiles show the maximum susceptibility above 350 ×10−8m3kg−1. The susceptibility decreases in profiles from the central part of Poland to 30–60. In the northern and southeastern part of the country the maximum observed susceptibility is about 10 ×10−8m3kg−1. Hysteresis parameters pointed at anthropogenic ferromagnetic minerals as a carrier of magnetic signal.

Thermal and magnetic properties of defects in the spin-gap compoundNaV2O5

The specific heat, magnetic susceptibility and ESR signals of a Na-deficient vanadate Na_xV_2O_5 (x=1.00 - 0.90) were studied in the temperature range 0.07 - 10 K, well below the transition point to a spin-gap state. The contribution of defects provided by sodium vacancies to the specific heat was observed. It has a low temperature part which does not tend to zero till at least 0.3 K and a high temperature power-like tail appears above 2 K. Such dependence may correspond to the existence of local modes and correlations between defects in V-O layers. The magnetic measurements and ESR data reveal S=1/2 degrees of freedom for the defects, with their effective number increasing in temperature and under magnetic field. The latter results in the nonsaturating magnetization at low temperature. No long-range magnetic ordering in the system of defects was found. A model for the defects based on electron jumps near vacancies is proposed to explain the observed effects. The concept of a frustrated two-dimensional correlated magnet induced by the defects is considered to be responsible for the absence of magnetic ordering.

Novel relation between Tc and low- T energy gap 2Δ o in Bi2212 and La214: an STS study

On the basis of electronic specific heat, magnetic susceptibility and STS data in La214, we report that a pseudogap of almost the same scale as the low- T ( T<< T c) gap Δ o will develop below T ∼ T co ≡ 2Δ o/4.3 k B in La214 as in Bi2212. We also report that over a wide hole doping p range in both systems, T c almost scales with pΔ o, and suggest that ∼ pΔ o will function as an effective energy gap in determining T c.

U2Co2Sn:An undoped non-Fermi-liquid system withCe≈γ−AT

Investigation of the low-temperature specific heat, magnetic susceptibility, and resistivity of ${\mathrm{U}}_{2}{\mathrm{Co}}_{2}\mathrm{Sn}$ for expected paramagnon behavior led instead to the discovery of a non-Fermi-liquid system obeying the Millis/Moriya theory prediction of an electronic specific heat that varies approximately as $\ensuremath{\gamma}\ensuremath{-}A\sqrt{T}$ over an appreciable temperature range, in this case over the whole temperature range (0.3--10 K) of measurement. The temperature dependence of the low-temperature resistivity, however, follows $\ensuremath{\rho}={\ensuremath{\rho}}_{0}{+AT}^{\ensuremath{\alpha}},$ with $\ensuremath{\alpha}(\ensuremath{\approx}1.8)$ lying below that predicted for a Fermi liquid (i.e., $\ensuremath{\alpha}=2)$ but above the $\ensuremath{\rho}={\ensuremath{\rho}}_{0}{+AT}^{1.5}$ predicted by the quantum phase transition, weakly interacting spin fluctuation theory of Millis/Moriya. Scaling of the specific heat with field indicates that the electron interactions responsible for the non-Fermi-liquid behavior are not single ion in nature. Several non-Fermi-liquid theories and their possible applicability to these results are discussed, as well as the possible influence of the relatively small U-U spacing in ${\mathrm{U}}_{2}{\mathrm{Co}}_{2}\mathrm{Sn}$ on the unusual non-Fermi-liquid behavior.

Dimerization of 3He in 3He-4He dilute mixtures filling narrow channels

We consider dimerization of ${}^{3}\mathrm{He}$ in a dilute solution of ${}^{3}\mathrm{He}$ in superfluid ${}^{4}\mathrm{He}$ filling straight narrow channels that can be found in nanoscale porous media. Dimer formation is facilitated by the restricted geometry and occurs despite the fact that in bulk fluid the interparticle interaction is too weak to lead to a bound state. Dimerization results in the effective ``bosonization'' of the system: a Bose quantum fluid of ${(}^{3}\mathrm{He}{)}_{2}$ arises in place of the ${}^{3}\mathrm{He}$ Fermi component. At high temperatures, when the ${}^{3}\mathrm{He}$ impurity quasiparticles form a Maxwell-Boltzmann gas, a drastic change in the thermodynamics occurs due to the presence of dimers. The specific heat and magnetic susceptibility of the ${}^{3}\mathrm{He}$ component, which we calculate at arbitrary degrees of dimerization, show a marked deviation from behavior expected of an undimerized ${}^{3}\mathrm{He}$ component. We show that the binding energy\char22{}which depends on the channel width\char22{}is expected to be sufficiently high to make experimental observation feasible. The presence of ${(}^{3}\mathrm{He}{)}_{2}$ dimers gives rise to an extra absorption mechanism for first sound propagating through the superfluid ${}^{4}\mathrm{He},$ due to resonant absorption and decay of dimers in the acoustic field. We have calculated the absorption coefficient. Several experiments suggest themselves, utilizing, perhaps, K-L zeolites or carbon nanotubes. If the dimers themselves turn out to be attractive, then quadrumers may appear: it may even be the case that a single ${}^{3}\mathrm{He}$ polymer will form over the entire length of the channel.

Characteristics of the thermodynamic and kinetic properties of NbH0.83 in the phase transition region

Measurements were made of the specific heat (in the temperature range 80–400 K), electrical resistivity (4.2–300 K), thermo-emf (4.2–300 K), thermal conductivity (7–300 K), magnetic susceptibility (4.2–400 K), and lattice parameters (30–300 K) of the alloy NbH0.83. The λ′→λβ phase transitions were studied. It was established that the structure of the niobium matrix of the hydride remains unchanged as a result of these transitions. It is shown that the β→λ phase transition (one-dimensional hydrogen ordering) is a three-stage one and is accompanied by a substantial change in the shear modulus of the hydride. The λ′ phase existing at T<110 K was determined. The electron thermal conductivity κel calculated for the λ′ phase in the range T<23 K is 25% higher than the measured thermal conductivity. In order to explain this fact and also the discontinuity in the concentration dependence of the coefficient of thermal expansion of NbHx for x≃0.83–0.84 and the approximately 1.5% compression of the NbH0.84 volume it is assumed that in the region of x c in the λ′ phase the topology of the Fermi surface of the NbHx interstitial alloy changes substantially.

Physical properties of Ba 2MnZn 2As 2O 2

We have measured the specific heat, electrical resistivity, and magnetic susceptibility of Ba 2MnZn 2As 2O 2. This phase has a magnetic transition at 30 K, and zero-field-cooled and field-cooled magnetic susceptibilities separate below this transition. The specific heat has a γT term suggesting a spin-glass-like state. The electrical resistivity is semiconducting with an activation energy of 1070 K, which rapidly decreases at the rate of −106 K/ GPa .

Metal–insulator transition in 1 T-TaS 2− xSe x

The transition metal dichalcogenide, 1 T-TaS 2, shows metal–insulator transition (MIT) accompanying the nearly commensurate (NC)–commensurate (C) charge density wave (CDW) phase transition at 180 K. It has been proposed that the low-temperature C-CDW phase is a Mott insulator. However, our specific heat and magnetic susceptibility measurements in the 1 T-TaS 2− x Se x system revealed no indications of effective mass enhancement or intrinsic localized spins in the insulating phase. So we propose a new model for the MIT in which the interlayer coupling of the CDW superstructure plays an important role.

Non-Fermi-liquid behavior in Kondo lattices induced by peculiarities of magnetic ordering and spin dynamics

A scaling consideration of the Kondo lattices is performed with account of singularities in the spin excitation spectral function. It is shown that a non-Fermi-liquid (NFL) behavior between two critical values of the bare $s-f$ coupling constant occurs naturally for complicated magnetic structures with several magnon branches. This may explain the fact that a NFL behavior takes place often in the heavy-fermion systems with peculiar spin dynamics. Another kind of a NFL-like state (with different critical exponents) can occur for simple antiferromagnets with account of magnon damping, and for paramagnets, especially with two-dimensional character of spin fluctuations. The mechanisms proposed lead to some predictions about behavior of specific heat, resistivity, magnetic susceptibility, and anisotropy parameter, which can be verified experimentally.

Evidence of field-induced non-Fermi-liquid behavior in YbCu 5− xAl x compounds

We measured the specific heat, magnetic susceptibility and electrical resistivity of YbCu 5− x Al x in magnetic fields up to 13 T. Between x=1.6 and 2 these compounds order antiferromagnetically with a Néel-temperature between 0.25 and 2 K, respectively. In high fields the antiferromagnetic transition is suppressed and a crossover to Fermi-liquid behavior occurs. At a critical field B cr, non-Fermi-liquid (nFl) behavior is found which is characterized by a −log T contribution to the specific heat C/ T down to 300 mK as well as deviations from T 2 behavior in the electrical resistivity. The magnetic susceptibility measured in B cr is proportional to 1− a√ T below 6 K. A scaling analysis of the specific heat and magnetization data obtained in higher fields ( B> B cr) points to collective effects responsible for the field-induced nFl behavior. This is the first system besides CeCu 6− x Ag x where field-induced nFl behavior is found.

Disappearance of magnetic moments in CePd 1− xNi xAl

We present the chemical pressure effect on the specific heat and magnetic susceptibility in the substituted system CePd 1− x Ni x Al. By substitution of 10% of Ni, T N has almost disappeared. Further substitution of Ni drastically diminishes the magnetic moment and the effective number of Bohr magnetons. The entropy integrated up to 10 K is 66% for CePdAl, and it decreases to 3% of R ln 2 with increasing x. The electronic specific-heat coefficient C/ T approaches 1.1 J/mol K 2 for CePd 0.9Ni 0.1Al at low temperatures. Single crystals for x=0.0 and 0.1 have been grown to investigate the magnetic anisotropy.

The non-Fermi-liquid behavior in magnetic Kondo lattices induced by peculiarities of spin dynamics

A scaling consideration of the Kondo lattices is performed with account of singularities in the spin excitation spectral function. It is shown that a non-Fermi-liquid (NFL) behaviour occurs naturally for complicated magnetic structures with several magnon branches. This may explain the fact that a NFL behaviour often takes place in the heavy-fermion systems with peculiar spin dynamics. The mechanisms proposed lead to some predictions about behaviour of specific heat, resistivity, magnetic susceptibility and anisotropy parameter, which can be verified experimentally.

Magnetic Excitations in Polyoxometalate Clusters Observed by Inelastic Neutron Scattering: Evidence for Anisotropic Ferromagnetic Exchange Interactions in the Tetrameric Cobalt(II) Cluster [Co4(H2O)2(PW9O34)2]10-. Comparison with the Magnetic and Specific Heat Properties

The ground-state properties of the tetranuclear Co2+ cluster [Co4(H2O)2(PW9O34)2]10- were investigated by combining specific heat, magnetic susceptibility, and magnetization measurements with a detailed inelastic neutron scattering (INS) study on a fully deuterated sample of K10[Co4(H2O)2(PW9O34)2]·22H2O. As a result of the single ion anisotropy of the octahedral Co2+, the appropriate exchange Hamiltonian of the Co4 spin cluster is anisotropic. INS turns out to be essential for the determination of energy splittings in the ground state resulting from the coupling. Besides the energy pattern, INS provides information about the wave functions of the split ground-state components of the spin cluster. Based on the Hamiltonian ĤAN = ∑i=x,y,z −2Ji(S1iS3i + S1iS4i + S2iS3i + S2iS4i) − 2J‘i(S1iS2i) the following set of parameters is obtained: Jz = 1.51 meV, Jx = 0.70 meV, Jz‘ = 0.46 meV, Jx‘ = 0.44 meV, r = 1.6, where r = Jx/Jy = Jx‘/Jy‘. These parameters also reproduce the magnetic specific heat, susceptibility...

Electronic Structure and Martensitic Transformation in Ni2MnGa Heusler Alloy

The ferromagnetic Ni2MnGa Heusler alloy is known to exhibit a martensitic transformation from cubic to tetragonal phase. The neutron studies [1, 2] established the existence of a weakly first-order structural phase transition at about 265 K. A number of studies have been concentrated on premartensitic transition. The results of elastic, thermal, and electron microscopy measurements clearly show the formation of premartensitic phase existing in the temperature range of 30-60 K above the martensitic transformation temperature [3]. The fact of the existence of premartensitic state is confirmed by the behaviour of the elastic constants [4, 5]: The elastic constant C' associated with the transverse acoustic (TA2) branch plays an important role in the structural transformation. The basic feature of this kind of transition is the instability of the phonon system, which leads to the crystal lattice rearrangement. The nearly complete softening m the (q, q, 0) TA 2 branch results in a premartensitic first-order transition which involves a commensurate periodic distortion of the parent structure Ni2MnGa with the periodicity equal to that of the soft mode [2]. The specific heat, elastic constants, and magnetic susceptibility in a ferromagnetic Ni2MnGa alloy exhibit anomalous behaviour [6, 7] at the temperature of condensation of the [110] TA2 phonon at the q = 0.33. But the phonon anomaly is not related to the magnetic ordering.

Quantification and Characterization of Maghemite in Soils Derived from Volcanic Rocks in Southern Brazil

AbstractMany soils developed from volcanic rocks in southern Brazil exhibit spontaneous magnetization caused by the presence of fine-grained maghemite (γ-Fe2O3), but few attempts were made to quantify or characterize this important soil component. To that end, clays were separated from freely drained soils derived from acid (≥63% SiO2), intermediate (54–62% SiO2), and basic (≤53% SiO2) igneous rocks produced by the Paraná flood volcanism. The sample set included soils with a wide range of pedogenic development on different landscape positions. The Fe oxide mineralogy of these samples was examined by using a combination of selective dissolution, magnetic susceptibility, and X-ray diffraction (XRD) techniques. Hematite and maghemite were the primary Fe oxides in mature soils (Oxisols, Ultisols, and Alfisols) developed from basic rocks; whereas goethite was dominant in all other soils, especially those formed from acid-intermediate rocks. The association of maghemite with basic rock materials suggests that it was primarily formed by oxidation of lithogenic magnetite. A strong, positive correlation (R2 = 0.89) was obtained between mass specific magnetic susceptibility (χ) of the clay fractions and maghemite contents estimated by XRD. Either method could be used for quantitative analyses, but χ was more sensitive than XRD at low maghemite concentrations (&lt;2 wt. %). The clay-sized maghem-ites were superparamagnetic with an estimated value for the mass specific magnetic susceptibility (χlf) value of 91,000 × 10−8 m3 kg−1 and frequency dependent variations of 10–15%. The maghemites also had low unit cell constants, which, if attributed entirely to replacement of Fe by Al, would correlate with Al substitutions in the range of 5–16 mole %. Selective dissolution of the soil maghemites was achieved by treatment of Fe oxide concentrates with 1.8 M H2SO4 at 75°C for 2 h.

Thermodynamics of CeNiSn at low temperatures and in weak magnetic fields

Detailed experimental and theoretical studies of the low-temperature specific heat, magnetic susceptibility, thermal expansion and magnetostriction of the orthorhombic compound CeNiSn are presented. All anomalies observed in the thermodynamic and magnetic properties of CeNiSn are explained in a framework of a model of metallic Kondo lattice with well developed spin-liquid-type excitations. The pseudogap behavior of these excitations appears due to interplay between spin-fermions and soft crystal-field (CF) states. The thermodynamic relations for the spin liquid are derived. Together with the explanation of inelastic neutron scattering spectra given earlier within a same approach these studies of the low-temperature thermodynamics and magnetic response give a consistent description of the nature of anomalies in the low-temperature thermodynamics of perfect and imperfect CeNiSn crystals.

Thermodynamics of the Superconducting Phase Transition inBa0.6K0.4BiO3

We suggest that the transition to superconductivity in a single crystal of Ba_{0.6}K_{0.4}BiO_3 with a T_c = 32K, and having critical fields with anomalous temperature dependencies and vanishing discontinuities in specific heat and magnetic susceptibility, may well be an example of a fourth order (in Ehrenfest's sense) phase transition. We have derived a free energy functional for a fourth order transition and calculated (for the temperature range ${T_c/2 < T \simeq T_c}$) the temperature dependence of the critical fields. We find $H_{c1}(T)\propto (1-T/T_c)^3, H_0(T)\propto (1-T/T_c)^2$ and $H_{c2}(T)\propto (1-T/T_c)^{1}$ in general agreement with experiments.

Dispersion of Nd spin correlations in heavy-fermion like Nd1.85Ce0.15CuO4

The T′-phase compound Nd2−xCexCuO4 exhibits at T&amp;lt;2 K resemblance with heavy-fermion behavior above a critical Ce content which has been established by specific heat, magnetic susceptibility, magnetoresistance, and μSR experiments and described qualitatively by the Zeeman route to heavy-fermion behavior. We present inelastic neutron scattering measurements at the onset of this doping regime at x=0.15 performed on a single crystal at T=0.05 K. The magnetic response from correlated Nd spins is reminiscent of the spin waves in Nd2CuO4. The dispersion of the Nd–Nd correlations has been determined in several Brillouin zones along the line ΓMAZΓ. Its medium energy is shifted to lower energies by more than 40% compared to the undoped compound. An energy gap of the Nd–Nd correlations is still observed but also an incipient soft mode has been found between the points A and M, which might indicate a magnetic instability. In addition, single-site scattering from slowly relaxing Nd spins contributes to the total magnetic scattering, indicating a hybridization of the Nd-4f electrons with the strongly correlated Cu-3d conduction electrons.

Magnetic properties of induced ferromagnet PrPtAl

The magnetic properties of orthorhombic PrPtAl with TiNiSi-type crystal structure and a nonmagnetic crystalline-electric field (CEF) ground-state singlet were investigated by measurements of specific heat, magnetic susceptibility, magnetization, and electrical resistivity. The results illustrate that in PrPtAl magnetic exchange interactions are strong enough to overcome the singlet–singlet CEF splitting of 21 K and to induce long-range magnetic order at TC=5.8 K.