Magnetic properties and structure of some ternary chromium chalcogenides with thallium and silver

The structure and magnetic properties of TlCrX₂ (X= S, Se, Te), Tl₃CrS₃, Tl₃Cr₃S₅, TlCr₃S₅, TlCl₅S₈ and AgCrO₂ have been investigated. TlCrS₂, TlCrSe₂ and Tl₃CrS₃ order ferromagnetically with Curie temperatures in the range 60–140 K. The other compounds are antiferromagnetics with negative paramagnetic Curie temperatures, whereas TlCrTe₂ is antiferromagnetic with a positive paramagnetic Curie temperature. In the case of the layered hexagonal TlCrS₂ and TlCrSe₂ owing to the great radius of the Tl-ion and the large Cr-Cr-distance the intralayer exchange interaction is positive giving rise to the ferromagnetic order. For AgCrO₂ the smaller intralayer Cr-Cr-distance gives rise to negative exchange interaction and antiferromagnetism.     

The specific heat of potassium holmium double tungstate

The results of measurements of thermal properties (specific heat) of potassium holmium double tungstate KHo(WO₄)₂ as a function of temperature (from 0.5 to 300?K) and magnetic field (up to 2?T) are presented. The total specific heat without the phonon and Schottky contributions is found to have the anomaly with maximum at T _SPT?～?5?K. This anomaly is likely related with the structural phase transition (SPT) caused by the cooperative Jahn–Teller effect. The increase of specific heat at very low temperatures and its shift towards high temperatures with increasing magnetic field are observed. The origin of this behaviour can be connected with possible magnetic phase transition induced by magnetic field.     

Specific heat of 1T-Ta0.93Ti0.07S2 in the Anderson localized states

The specific heat of 1T-Ta_0.93Ti_0.07S₂ in the Anderson localized states has been measured from 0.2 to 5.0 K in magnetic fields up to 60 kOe. Below 3.5 K, a Schottky type excess specific heat was observed, depending on the magnetic field. This excess specific heat is explained on the basis of both the Coulomb interactions between different Anderson localized states as well as in the same state.     

Low temperature thermodynamical properties of ErCu2Si2

ErCu₂Si₂ crystallises in the tetragonal ThCr₂Si₂-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50 K an additional incommensurate magnetic structure was observed. The propagation vector k=(0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated.     

Specific heat below 1k some examples in magnetism

The measurement of specific heat below 1 K by means of a quasi-adiabatic calorimeter, employing adiabatic demagnetization for cooling, is described. The lattice, hyperfine and electronic contributions in the temperature domain 0.05 < T < 4 K are discussed briefly as an introduction to the analysis and exploitation of the magnetic contribution to the specific heat in magnetic insulators. The comparison with simple magnetic models is illustrated by the analysis of the specific heat data of the NdMO₃ perovskites, with M = nonmagnetic atom. The action of a magnetic field, albeit an internal field, is discussed using NdMO₃, M = Fe, Cr and Ni perovskite as examples. Finally, two molecular magnetic materials are discussed; Gd₂(ox)[Cu(pba)]₃[Cu(H₂O)₅]· 20H₂O as a candidate for ferromagnetic order in a rare earth transition metal complex, and Gd(hfac)₃NITR, with the nitronyl nitroxide magnetic radical interacting with the rare earth.     

Specific heat and magnetic susceptibility of MnF2 and Mn0.98Fe0.02F2 near TN

The antiferro- to paramagnetic phase transition of the weakly anisotropic compound MnF₂ has been studied by means of heat capacity, magnetic susceptibility and thermal expansion measurements. The critical-point parameters associated with the specific heat indicate a transition according to the theoretical Ising-model. The temperature derivative of the parallel magnetic susceptibility times temperature (d(χ∥T)/dT) and the c-axis thermal expansion coefficient show a critical behaviour very similar to that of the specific heat. The influence of iron doping on the critical behaviour has been investigated by studies on Mn_0.98Fe_0.02F₂. Specific heat and magnetic susceptibility measurements show an unexpectedly sharp transition although some rounding off is noticed as compared to pure MnF₂.     

A magnetic study of the ThCr2Si2-type RPd2Ge2 (R=Pr, Nd) compounds. Magnetic structure of PrPd2Ge2 from powder neutron diffraction

The magnetic properties of the PrPd₂Ge₂ and NdPd₂Ge₂ compounds have been investigated by magnetic measurements, specific heat measurements and neutron diffraction experiments. The PrPd₂Ge₂ compound orders antiferromagnetically below T_N=5.0(2) with an original modulated magnetic structure characterized by a magnetic cell three times larger than the chemical one by tripling of the c parameter. The palladium atom is non magnetic and the Pr moments are parallel to the c-axis with a value of ≈2.0 μ_B at 2 K. The specific heat measurements clearly detect a low temperature transition for the NdPd₂Ge₂ compound, interpreted as a Nd sublattice antiferromagnetic ordering below 1.3(2) K.     

具有非磁性缺陷的二维自旋玻璃模型

本文提出具有非磁性缺陷(n_m^1/2l<<1)的二维RKKY自旋玻璃模型,分别给出不同温区比热和磁化率的表达式.同时应用渗流理论分析转变温区自旋集团的行为,说明比热膝盖伏峰值和磁化率尖拐状峰值的实验事实. 关键词：     

Anomalous behavior of the specific heat and upper critical magnetic field in the superconducting single crystal La1.85Sr0.15CuO4

The specific heat and resistive upper critical magnetic field of the single crystal La_1.85Sr_0.15CuO₄ are investigated in the temperature range 2–50 K in magnetic fields up to 8 T for two directions of the magnetic field, parallel and normal to the ab crystalline plane. For both orientations a nonlinear (close to square root) magnetic field dependence of the mixed-state specific heat and a positive curvature of the temperature dependence of the upper critical magnetic field are observed. Neither of these anomalies is described by standard theories of superconductivity. Within the framework of the thermodynamic relations it is shown that in a type-II superconductor a relationship exists between the temperature dependence of the critical magnetic field and the field dependence of the specific heat. The anomalies observed in these phenomena are interrelated. Zh. éksp. Teor. Fiz. 112, 1386–1395 (October 1997)     

Magnetic and transport properties of Pr2Pt3Si5

We have investigated the magnetic and transport properties of a polycrystalline Pr₂Pt₃Si₅ sample through the dc and ac magnetic susceptibilities, electrical resistivity, and specific heat measurements. The Rietveld refinement of the powder X-ray diffraction data reveals that Pr₂Pt₃Si₅ crystallizes in the U₂Co₃Si₅-type orthorhombic structure (space group Ibam). Both the dc and ac magnetic susceptibility data measured at low fields exhibit sharp anomaly near 15 K. In contrast, the specific heat data exhibit only a broad anomaly implying no long range magnetic order down to 2 K. The broad Schottky-type anomaly in low temperature specific heat data is interpreted in terms of crystal electric field (CEF) effect, and a CEF-split singlet ground state is inferred. The absence of the long range order is attributed to the presence of nonmagnetic singlet ground state of the Pr³⁺ ion. The electrical resistivity data exhibit metallic behavior and are well described by the Bloch–Grüniesen–Mott relation.     

Specific heat of EuIn2P2 at high magnetic fields

We have carried out specific heat measurements on EuIn₂P₂ at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear λ-type anomaly due to a magnetic transition at , indicating that the magnetic transition is of second-order. The λ-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu²⁺ magnetic moments align ferromagnetically perpendicular to the c-axis below T_C. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu²⁺ multiplet by internal magnetic fields.     

Field dependent specific heat and longitudinal magnetization of the quantum magnet layer Cs2CuCl4: Anisotropy effects

We have addressed the specific heat and magnetization of an anisotropic spin-1/2 triangular Heisenberg antiferromagnet Cs₂CuCl₄ in the presence of magnetic field at finite temperature. We have investigated the behavior of thermodynamic properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on thermodynamic properties has also been studied via the bosonic model by Green’s function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the specific heat and longitudinal magnetization in the gapped field induced spin-polarized phase for various magnetic fields and anisotropy parameters. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. Our results show temperature dependence of specific heat includes a peak so that its temperature position goes to higher temperature with increase of magnetic field. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum.     

The specific heat of C-phase Gd2O3

The specific heat of C-phase (almost cubic) Gd₂O₃ has been measured between 1.4 and 18 K. It shows a broad peak at 2.0 K. While the peak can be fit by a Schottky specific heat curve, the weight of all the experimental evidence to date indicates that the specific heat is due to magnetic ordering of the Gd⁺⁺⁺ ions. The implications of the results on the technological applications of C-phase Gd₂O₃ are discussed.     

Magnetische und kalorische Eigenschaften von Alkali-Hyperoxid-Kristallen

The phase transitions of Alkali-Hyperoxide crystals (NaO₂, KO₂, RbO₂, and CsO₂) grown in liquid ammonia have been investigated by means of the following measurements:

1. magnetic susceptibility
2. differential magnetic susceptibility as magnetic field
3. magnetization curve in static and pulsed fields
4. specific heat.

The anomalies of the specific heat could be correlated with the magnetic properties and structural changes. Several new phase transitions were found. The magnetic behaviour of NaO₂ indicates magnetic order (of as yet unknown nature) at low temperatures. The magnetic and caloric behaviour of KO₂ at low temperatures is compatible with a Néel point at 7 K. A metamagnetic transition can be induced at temperatures below 12 K with fields of about 70 kOe. This transition is connected with structural changes. RbsO₂ and CO₂ are probably antiferromagnetic with Néel temperatures of 15 K and 9.6 K, respectively.     

Heat capacity and magnetic susceptibility of ReO3

The specific heat and magnetic susceptibility of the transition metal oxide ReO₃ have been measured. The specific heat results give a Debye temperature Θ_D = 460 ± 10 K and an electronic specific heat coefficient γ = 6.45 ± 0.07 cal/mole K² which are in good agreement with similar measurements on the cubic sodium tungsten bronzes. The magnetic susceptibility and the electronic contribution to the specific heat are within a few percent of the corresponding parameters calculated from the free electron model with one electron per unit cell. Our results show that ReO₃ behaves much like a simple metal. No experimental evidence for narrow d-band effects was observed.     

Nouvelles donnes experimentales sur les proprietes magnetiques de Cr3 Se4 et des solutions solides Cr3 Set S4−t

Magnetic susceptibility and specific heat measurements and neutron diffraction experiments allow to locate Néel temperatures T_N and also two types of transitions below T_N. At T_t of order T_N/2 the susceptibility is maximum, and the magnetic structure is modified (for Se-rich compounds). The second transition takes place around 15 K and is characterized by a specific heat peak and a susceptibility anomaly but no modification of the magnetic structure, according to our powder diffraction data.     

Low temperature specific heat of bi-layered manganites La2−2xSr1+2xMn2O7 (x=0.3 and 0.5)

The specific heat (C) of bi-layered manganites La_2−2xSr_1+2xMn₂O₇ (x=0.3 and 0.5) is investigated for the ground state of low temperature excitations. A T^3/2 dependent term in the low temperature specific heat (LTSH) is identified at zero magnetic field and suppressed by magnetic fields for x=0.3 sample, which is consistent with a ferromagnetic metallic ground state. For x=0.5 sample, a T² term is observed and is consistent with a two-dimensional (2D) antiferromagnetic insulator. However, it is almost independent of magnetic field within the range of measured temperature (0.6-10 K) and magnetic field (6 T).     

Magnetic and transport properties of Pr2Pd3Si5

We have investigated the magnetic and transport properties of a new ternary intermetallic compound Pr₂Pd₃Si₅ which forms in U₂Co₃Si₅-type orthorhombic structure (space group Ibam). At low field (0.01 T) magnetic susceptibility exhibits an abrupt increase below 7 K and peaks at 5 K, revealing a magnetic phase transition. The onset of magnetic order is also confirmed by well defined anomalies in the specific heat and electrical resistivity data. Apart from the sharp λ-type anomaly, magnetic part of specific heat also shows a broad Schottky-type hump due to crystal field effect. Magnetoresistance data as a function of temperature exhibits a pronounced peak in paramagnetic state which could be interpreted in terms of crystal field effect and short-range ferromagnetic correlations.     

Quasiparticle density of states of 2H-NbSe2 single crystals revealed by low-temperature specific heat measurements according to a two-component model

Low-temperature specific heat in a dichalcogenide superconductor 2H-NbSe2 is measured in various magnetic fields. It is found that the specific heat can be described very well by a simple model concerning two components corresponding to vortex normal core and ambient superconducting region, separately. For calculating the specific heat outside the vortex core region, we use the Bardeen-Cooper Schrieffer （BCS） formalism under the assumption of a narrow distribution of the superconducting gaps. The field-dependent vortex core size in the mixed state of 2H-NbSe2, determined by using this model, can explain the nonlinear field dependence of specific heat coefficient γ（H）, which is in good agreement with the previous experimental results and more formal calculations. With the high-temperature specific heat data, we can find that, in the multi-band superconductor 2H-NbSe2, the recovered density of states （or Fermi surface） below Tc under a magnetic field seems not to be gapped again by the charge density wave （CDW） gap, which suggests that the superconducting gap and the CDW gap may open on different Fermi surface sheets.     

Kondo lattice and heavy fermions in Heusler phases: CeInAg2−xCux

Magnetic properties, electrical resistivity, specific heat and magnetic excitations have been investigated in Heusler phases CeInAg_2–xCu_x. The hybridization continuously increases from CeInAg₂ (antiferromagnetic Kondo lattice) to CeInCu₂ (heavy fermion compound). The specific heat coefficient for this last compound is found to reach 1.2 J/mole. K² at 1.4 K, the Kondo temperature is 6 K and the Wilson ratio is close to 2.