Previous Specific Heat Research Articles

Stability of the modulated states inErNi2B2C: A neutron diffraction study of chemically doped samples

Neutron-diffraction measurements on ${\mathrm{Er}}_{0.8}{R}_{0.2}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ $(R=\mathrm{Tb},\mathrm{Lu})$ and $\mathrm{Er}{\mathrm{Ni}}_{1.9}{\mathrm{Co}}_{0.1}{\mathrm{B}}_{2}\mathrm{C}$ have been carried out to investigate the influence of chemical doping on the stability of the modulated states in $\mathrm{Er}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$. Within the magnetically ordered phase and down to $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ (the lowest measured temperature), the powder diffractograms of Lu and Tb doped compounds are consistent with a transverse sine-modulated (fundamental) mode. A neutron diffraction study on a single-crystal ${\mathrm{Er}}_{0.8}{\mathrm{Lu}}_{0.2}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ recorded at $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ has confirmed the absence of higher order harmonics. In contrast, the low-temperature patterns of the Co doped compound reveal the presence of all the odd-order harmonics up to the fifth-order satellite, reminiscent of the structure of the undoped $\mathrm{Er}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ below the weak-ferromagnetic transition point ${T}_{\mathit{WF}}=2.1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$: a squared-up, noncompensated long-period antiferromagnetic state. The above-mentioned findings are consistent with the conclusions drawn from our previous specific-heat and magnetization measurements on the same compounds: on lowering the temperature further below ${T}_{N}$, both $\mathrm{Er}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ and Co doped compounds undergo a spontaneous transition at ${T}_{\mathit{WF}}$. In contrast, for the Lu and Tb doped compounds, no such second magnetic phase transition was observed down to $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$; eventually the squaring-up of these structures, as required by entropy arguments, should occur but at temperatures lower than $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

First-principles study on the electronic and magnetic properties of perovskite ruthenate SrRuO 3

We report a self-consistent full-potential LMTO band structure calculation on the electronic and magnetic properties of Ru-based perovskite SrRuO 3 in this article. For the assumed simple cubic structure with lattice constant a=0.3923 nm , the calculated spin moment per SrRuO 3 unit is 1.29 μ B. Most of the moment (approximately 65%) is located on the Ru site within a unit cell and the spin moment of each oxygen atom is about 0.10 μ B. The electronic density of states at Fermi level E F is about 43.5 (states/Ry/f.u.). For the practical orthorhombic structured SrRuO 3, the present calculation predicts a spin moment ∼1.08 μ B/f.u. and the corresponding DOS at Fermi level is ∼61.0 (states/Ry/f.u.). The present band calculation yields a reasonable enhancement of electron mass in comparison with a previous specific heat measurement at low temperature. It is concluded that SrRuO 3 is a typical itinerant ferromagnet instead of a highly correlated electron system.

Electron Spin Resonance Study of Cu Benzoate Using a3He–4He Dilution Refrigerator

An electron spin resonance (ESR) measurement system for use at ultralow temperatures using a 3 He– 4 He dilution refrigerator has been developed. As the first experiment, the ESR was measured on a quantum spin chain Cu benzoate down to 160 mK, in which a field-induced gap was recently found. [rf_4] The evaluation of a new ESR mode, the so-called breather mode, was found at the lowest temperatures. In the previous ESR down to 0.5 K, this mode was clearly found for H ∥ c , in which the magnitude of the gap is largest. In the present work, the achievement of low temperatures enabled us to observe a smaller gap in H ∥ b by suppressing the thermal excitation. The magnitude of the field-induced gap evaluated from the nonlinear field dependence of the mode shows good agreement with that determined by previous specific heat measurements.

The vibrational density of states revisited in the archetypical icosahedral quasicrystal Al62Cu25.5Fe12.5

We have studied the phonon dynamics of icosahedral i-Al62Cu25.5Fe12.5 using inelastic neutron scattering (INS) in isotope-doped samples, and have combined this with previous inelastic nuclear-resonant absorption (INA) of synchrotron radiation measurements. We are able to show that the maximum in the vibrational density of states (VDOS) at 14 meV is heavily weighted by copper. The INA results have shown that the upper peak at 27 meV is dominated by iron. We are able to explain previous lattice specific heat results from the low-energy region of the neutron-weighted VDOS, including the non-integer power behaviour.

Heavy electron and giant exchange YbNiBC: Yb Mössbauer spectroscopy and magnetization studies

We report low temperature 170Yb Mossbauer spectroscopy and magnetization measurements on two tetragonal non-superconducting quaternary borocarbides, YbNi2B2C and YbNiBC, and present LIII edge X-ray absorption data in YbNiBC. Both compounds show evidence of 4f-conduction band hybridisation. In the heavy electron YbNi2B2C, measurements down to 0.023 K show that only a small hyperfine interaction is present and we estimate an upper limit of 0.05–0.1 μ B for any Yb moment. In YbNiBC, magnetic ordering is observed below 4.2 K, in agreement with previous specific heat measurements. The single ion easy magnetization axis lies along the c axis but the ordered Yb moments lie in the basal (a, b) plane. Their (extrapolated) saturated value is unusually low (0.35 μ B). The Yb-Yb exchange interaction is very large and highly anisotropic with the dominant component lying in the basal plane. We also report 166Er Mossbauer and specific heat data in the ferromagnet ErNiBC.

A Mössbauer spectroscopy and -edge study of the Kondo lattice

We present a detailed study of the magnetic and crystal-field properties of the hexagonal Kondo lattice , using Mössbauer spectroscopy in the temperature range 0.1 K - 50 K. -edge x-ray absorption spectra at 10 K and 300 K were also obtained; they indicate that the Yb ion is very close to trivalent over the whole temperature range. In the antiferromagnetic phase, the thermal variation of the spontaneous moment has been measured and the derived transition temperature is in agreement with previous specific heat and magnetic data. In the paramagnetic phase, the two components and of the g-tensor of the ground crystal-field doublet have been measured. These g-values cannot be accounted for by a crystal-field-only model, and we interpret this in terms of a Kondo reduction of the paramagnetism and of the spontaneous moment , with a Kondo temperature . In addition, the spectra in the antiferromagnetic phase show inhomogeneous broadenings due to the presence of random distortions with respect to the hexagonal Yb site symmetry, and, close to , dynamical effects are clearly evident and allow the fluctuation frequency to be measured in the magnetically ordered phase.

Neutron Diffraction Study of Antiferromagnetic Order in the Kondo Compound CePdSn

Successive phase transitions in the Kondo compound CePtSn are studied by neutron scattering experiments on a single-crystalline sample. Antiferromagnetic phase transitions are observed at T N =6.2 K and T M =3.8 K, which are second and first order transitions, respectively, in accord with the previous specific heat measurement. The magnetic structure is a single- Q type S n ν = a ν e i k · R n + a ν * e - i k · R n with incommensurate modulation vectors k =0.466 b * and 0.418 b * in the low ( T < T M ) and intermediate ( T N < T < T M ) temperature phases, respectively. The polarization vectors a ν cannot uniquely be determined from scattering intensities, and thus those which reproduce the intensities are selected using a maximum entropy method. In the low-temperature phase, the polarization vectors have a , b and c components, and the root mean square of the moment is m rms =0.84± 0.08 µ B ( m a rms =0.72, m b rms =0.31, m c rms =0.29 µ B ) at T =2 K. In the intermediate-temperature phase, the polarizat...

Elastic properties in the heavy-fermion superconductor UPd2Al3

Abstract Elastic constants and thermal expansion on UPd2Al3 have been measured. Elastic constants exhibit anomalies around TN = 14.5 K and Tc = 1.8 K. Anomalous behaviors around 0.6 K in C11, C33 and thermal expansion are consistent with previous specific heat measurements. Superconducting Gruneisen constants possess large values of ωa = 23 and Ω c =47 .

Neutron Diffraction Study of Antiferromagnetic Order in the Kondo Compound CePtSn

Successive phase transitions in the Kondo compound CePtSn are studied by neutron scattering experiments on a single-crystalline sample. Antiferromagnetic phase transitions are observed at T N =6.2 K and T M =3.8 K, which are second and first order transitions, respectively, in accord with the previous specific heat measurement. The magnetic structure is a single- Q type S n ν = a ν e i k · R n + a ν * e - i k · R n with incommensurate modulation vectors k =0.466 b * and 0.418 b * in the low ( T < T M ) and intermediate ( T N < T < T M ) temperature phases, respectively. The polarization vectors a ν cannot uniquely be determined from scattering intensities, and thus those which reproduce the intensities are selected using a maximum entropy method. In the low-temperature phase, the polarization vectors have a , b and c components, and the root mean square of the moment is m rms =0.84± 0.08 µ B ( m a rms =0.72, m b rms =0.31, m c rms =0.29 µ B ) at T =2 K. In the intermediate-temperature phase, the polarizat...

Spin-wave excitations and the magnetic phase transition in the ytterbium monopnictide YbAs

Low-temperature neutron scattering experiments have been performed to investigate spin-wave excitations and the magnetic phase transition in the Kondo compound YbAs. In agreement with previous Mossbauer and specific heat experiments the present neutron results suggest that YbAs undergoes a first-order magnetic phase transition, which is smeared out in the crystal in an unusually large temperature range between 0.48 and 0.65 K. The spin-wave dispersion determined by bilinear magnetic exchange interactions is much stronger than the observed molecular-field splitting Delta MF. This indicates that due to Kondo hybridization in YbAs the onset of long-range magnetic ordering is strongly suppressed and shifted to lower temperature. The mean-field spin-wave model for localized 4f electron systems which was appropriate to describe the magnetism of the dense Kondo systems CeAs and CeSe fails to describe the magnetism in YbAs. This result is not surprising because of the strong reduction of the observed magnetic moment of YbAs with respect to the crystal-field expectation value.

Magnetic energy in a dilute two-dimensional Heisenberg ferromagnet K2CuxZn1-xF4: linear optical birefringence measurements

The authors report on linear birefringence (LB) measurements in the dilute archetypal 2D Heisenberg ferromagnet K2CuxZn1-xF4 in the whole concentration range 0<x<1. From the temperature dependence of the LB in the range 1.3-300 K, which is separated into two parts (the lattice contribution and the magnetic contribution), they discover information on the influence of the Jahn-Teller effect and on the change in the magnetic dimensionality with dilution. Moreover, they confirm previous specific heat results at low temperatures. Since the magnetic LB is proportional to the magnetic energy, they determine and explain its dependence on dilution.

Magnetic properties of amorphous and liquid Ni-P-B alloys

In order to study the change of the magnetic properties upon the transition from the Ni-B to the Ni-P system, the amorphous alloy series Ni 81.5P x B 18.5− x with x = 0, 1.8, 3.7, 7.4, 13, 16.7 and 18.5 at% were prepared by the melt-spinning technique. First, the magnetization isotherms were measured for the amorphous state from 5 to 300 K in magnetic fields up to 9 kOe. For the alloys with 3.7 ⩽ x ⩽ 18.5, a Pauli susceptibility could easily be deduced for the amorphous matrix. For x = 0 and 1.8, nonlinear magnetization curves were obtained which could not be saturated up to 9 kOe; however, based on previous 11B NMR and magnetization studies on another amorphous Ni 81.5B 18.5 alloy, these two alloys are also considered to be Pauli paramagnetic. Second, the magnetic susceptibility in 17 kOe magnetic field was measured as a function of temperature from 300 to 1600 K yielding crystallization temperatures of the amorphous alloys and the susceptibilities of the liquid state. These latter values were in good agreement with the Pauli susceptibilities of the amorphous state. Based on these data and on the results of previous low-temperature specific heat studies on the same alloys, the electronic structure of these metallic glasses is discussed.

Magnetic susceptibility, magnetization and specific heat of Mn 3.2Ga 0.8N

An analysis of previous magnetic susceptibility, specific heat and magnetization data as well as of new magnetization results here reported on Mn 3.2Ga 0.8N, is performed. The smearing out of the heat capacity anomaly, the susceptibility shape at the ferrimagnetic ordering temperature T c(235.±5.) K, and the presence of significant remanent magnetization above T c is analysed assuming small differences of stoichiometry through the sample. Furthermore, the magnetic behaviour at temperatures below T A(143.±6) K is explained assuming a coexistence of ferrimagnetic and spin glass ordering.

Specific-heat measurements of Pd in magnetic fields to 20 T

We report accurate measurements of the specific heat of zone-refined, high-purity Pd between 6 and 17 K in fields of 10, 15, and 20 T. The change of the specific heat of this Pd in 20 T, averaged over the 14 different temperatures of measurement, compared with zero-field measurements at the same temperatures, is +1.0%. Within our limits of error ( +- 2%), the results directly contradict previous specific heat results on Pd in fields to 11 T by Hsiang et al.

Electronic structure and atomic arrangement in VPt system

We present a study on the electronic structure of Pt and ordered compounds in the V-Pt system, based on photoemission (XPS and UPS) measurements and on the examination of previous susceptibility and specific heat results. Photoemission spectra on pure Pt are discussed. The experimental results of compounds allow an evaluation of the partial densities of states (PDOS's) in particular for Platinum. The shape of this PDOS varies appreciably with Pt concentration and can be analyzed in terms of local environments and local symmetry in the various compounds. For “isolated” Pt atoms in a Vanadium environment (V 3Pt) the Pt electronic states are mainly located toward the bottom of the valence band. With an increasing of Pt neighbours a broad contribution appears in the middle of the band and is attributable to Pt-Pt hybridization ; more and more electronic states are available in the upper part of the band An evaluation of the PDOS's at the Fermi level n(E F)'s is presented. It is suggested that n(E F) for Vanadium is constant for V, V 3Pt and VPt and decreases for VPt 2 whereas the Pt n(E F) increases slowly from V 3Pt to VPt 2 and increases rapidly from VPt 3 to Pt.

Photoemission, NMR, susceptibility and specific heat in V and A15 V 3Pt

We present a study on the electronic structure of V and V 3Pt, based on photoemission (XPS and UPS) measurements and on the examination of previous band calculations, specific heat, susceptibility and NMR results. Photoemission spectra on pure V, in particular the XPS one, show a good agreement with band calculations ; the He II spectrum exhibits a strong satellite which could be attributed to a simple Auger effect or to a resonant process. Photoemission on V 3Pt allows an evaluation of the partial densities of states (PDOS) ; the Vanadium PDOS is similar to that of pure element, at least for the upper part of the valence band ; meanwhile the Platinium partial EDOS is drastically modified. This can be understood in the framework of electronic structure of compounds involving early and late transition metals where the atomic structure seems to play an important role. An evaluation of the EDOS's at the Fermi level n(E F) can also be tempted and compared to those obtained from the other mentioned techniques. Therefore it is suggested that for Vanadium n(E F) is similar to that of pure element ; for Platinium n(E F) is strongly reduced. Finally the analysis of the electronic specific heat of V, Pt and V 3Pt indicates that the parameter of electron-phonon coupling determined by the Mc Millan's theory is likely underesti:ated, due to the occurence of an estimated coupling in V and V 3Pt.

Analysis of the paramagnetic susceptibility of Fe(HCOO) 2·2H 2O

The paramagnetic susceptibility of powdered Fe(HCOO) 2·2H 2O is analysed by the combined method of high temperature expansion and molecular field approximation. The experimental data are well explained by the consistent model obtained in the previous specific heat analysis.

Evidence for valence fluctuation in the CeSn3compound

Presents the experimental results of magnetisation, magnetic susceptibility (at normal pressure and under a pressure of 6 kbar), electrical resistivity and thermal expansion performed on a single sample of CeSn3. These measurements were done over the temperature range of 1.4<T<300K. The author used an extension of the Ramirez-Falicov theory outlined by Alascio et al. (1972, 1973) to show that these and previous specific heat and thermopower results can be related by including a mixing between the two possible Ce configurations.

Photoemission and electronic structure of crystalline Co3B and amorphous Co - P - B

Abstract We present an XPS and UPS study of crystalline Co, Co 3 B and Co 78 P 14 B 8 glassy metal. For Co 3 B the electronic distribution curves (EDC) of the valence band and the previous specific heat and magnetic results are interpreted in a qualitative model where : i) the s-p cobalt-boron bonding states lie in the low part of the band, the upper levels being mainly cobalt d states and ii) a large density of states of the majority spin band is present at the Fermi level. For amorphous Co 78 P 14 B 8 the EDC shows that E F is located in a high density of states region, it is suggested that the phosphorus p states ae centred at 7.5 eV. The photoemission and the magnetic results can be also interpreted in the framework of the previous model.

Low-temperature specific heat anomalies in the group V transition metals

Anomalies previously reported in the specific heat curve of normal-state niobium at 3 and 9.5 K prompted new measurements on single crystals of niobium, tantalum, and vanadium from their superconductingT c 's up to 20 K. The upper anomaly was confirmed in Nb and found to occur at 10.3 K. At this temperature theC/T vs. T 2 curve changed abruptly from a line with constants γ 2 =7.67 mJ/K 2 mole and θ 2 =241 K to one with γ 3 =9.16 mJ/K 2 mole and θ 3 =250 K. The NbT c was 9.275 K. Anomalies similar to that occurring at 3 K in the niobium curve were discovered to exist in tantalum and vanadium as well, but at the higher temperatures of 7.19 and 7.47 K, respectively. The tantalum data yielded line constants of γ 1 =5.42 mJ/K mole, θ 1 =238 K, γ 2 =4.36 mJ/K 2 mole, and θ 2 =228 K and aT c of 4.475 K. For vanadium θ 1 =397 K is higher than previous specific heat values of θ 1 =382 K, and in agreement with that obtained from elastic constant measurements (399 K). The discontinuities in the slopes of the specific heat curves are analyzed in terms of anomalies in the electron and phonon spectra of the materials investigated.