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Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12 and AgCa2Ni2V3O12 has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39 K for AgCa2Co2V3O12 and 7.21 K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TN correspond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20 K per mol Co2+ and Ni2+ ions are 5.31 J K−1 mol-Co2+-ion−1 and 6.85 J K−1 mol-Ni2+-ion−1, indicating S=1/2 for Co2+ ion and S=1 for Ni2+ ion. The magnetic susceptibility of AgCa2Ni2V3O12 shows the Curie-Weiss behavior between 20 and 350 K with the effective magnetic moment μeff=3.23 μB Ni2+-ion−1 and the Weiss constant θ=−16.4 K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state 2E(t26e) and the first excited state is spin quartet state 4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ ion is verified experimentally at least below 20 K which is in agreement with the result of the heat capacity.  相似文献   

4.
The time fluctuations of the pair correlations in the amorphous spin glass Al2Mn3Si3O12 were investigated by quasi-elastic neutron scattering. Their time constant follows an Arrhenius law from room temperature down to below the spin glass temperatureT f. No static component of the pair correlation was found. It is shown that an Arrhenius law can qualitatively account for all the phenomena associated with the ac susceptibility as a function of temperature, ac frequency and applied dc magnetic field.Dedicated to Professor Jagodzinski on the occasion of his 65th birthday  相似文献   

5.
Quantum-critical behavior of the itinerant electron antiferromagnet (V0.9Ti0.1)2O3 has been studied by single-crystal neutron scattering. By directly observing antiferromagnetic spin fluctuations in the paramagnetic phase, we have shown that the characteristic energy depends on temperature as c1 +c2T3/2, where c1 and c2 are constants. This T3/2 dependence demonstrates that the present strongly correlated d-electron antiferromagnet clearly shows the criticality of the spin-density-wave quantum phase transition in three space dimensions.  相似文献   

6.
The metal-to-insulator transition in V2O3 is described by a model that is based on the electronic band structure of this material. The vanadium 3d-t 2g band decomposes in the trigonal symmetry into two bands, a 1g and e π. The a 1g band consists of orbitals connecting pairs of c-axis neighbouring atoms, while the e π band consists of orbitals in the plane perpendicular to the c-axis. The change in distance between c-axis neighbours changes the nature of the a 1g band from molecular (delocalized) to atomic (localized). The localization of the a 1g electrons causes through the atomic exchange interaction also the localization of the e π electrons, and this localization creates a gap in the e π band which causes the material to become insulating. This model is treated in the Hartree-Fock approximation (the ‘Excitonic’ model) at zero and finite temperatures, and various aspects of the transition, such as changes in the c/a ratio, the creation of magnetic moments, changes in covalency, the effect of pressure and the order of the transition, are investigated.  相似文献   

7.
We report the first systematic study of the electrical transport and magnetic properties of BaRu6O12, which has a quasi-one-dimensional (quasi-1D) hollandite structure. We show that BaRu6O12 is quasi-1D electronically as well. Its physical properties were found to be extremely sensitive to disorder. Furthermore, a transition from being metallic with a resistance drop around 2 K to being weakly insulating as the applied magnetic field was increased was also found. We propose that these two features are related to the possible presence of a quantum phase transition in this material system.  相似文献   

8.
Muon spin precession is observed in the ordered state of antiferromagnetic oxides MnO and V2O3. An anomalous temperature dependence of muon precession frequency and the absence of critical behavior atT N are found in MnO and a hysterisis of the transition temperature is observed in V2O3. These results are explained in terras of the crystal distortion of these materials belowT N.We would like to thank Dr. T. Suzuki, Dr. S. Takagi, Dr. Y. Kuno and Dr. C.Y. Huang for their help in the measurements, and Dr. K. Kosuge and Dr. S. Kachi for providing the specimen of V2O3. We are grateful to the financial support from Japan Society for Promotion of Science.  相似文献   

9.
A first-order transition at 290 K in LiMn2O4 with a cubic spinel-type structure is known to degrade the electrochemical performance of the positive electrode of rechargeable lithium-ion batteries. Using first-principles density functional theory (DFT), we confirm that the phase transition is induced by charge-ordering of Mn3+/Mn4+ accompanied by orbital-ordering due to Jahn–Teller distortion, which is in agreement with the previous experimental results of Rodríguez-Carvajal et al. [J. Rodríguez-Carvajal, G. Rousse, C. Masquelier, M. Hervieu, Phys. Rev. Lett. 81 (1998) 4660]. The optimized structure of the low-temperature (LT) phase has orthorhombic symmetry with five distinct crystallographic sites for Mn. The spin integration at each Mn site shows that Mn3+ resides at three Mn sites and the remaining two sites are occupied by Mn4+ ions. Total energy calculations indicate that the LT phase is about 0.23 eV/ LiMn2O4 more stable than cubic LiMn2O4 (high-temperature phase). The electrochemical Li extraction reaction from the LT phase is also investigated using DFT calculations. The results indicate that the reaction is initially divided into two voltage regions. Electrostatic interactions in the LT phase are calculated using a point charge model, accounting for the features of the electronic configurations and electrochemical reactions.  相似文献   

10.
The 55Mn nuclear magnetic resonance spectrum of noncollinear 12-sublattice antiferromagnet Mn3Al2Ge3O12 has been studied in the frequency range of 200–640 MHz in the external magnetic field H ‖ [001] at T = 1.2 K. Three absorption lines have been observed in fields less than the field of the reorientation transition H c at the polarization hH of the rf field. Two lines have been observed at H > H c and hH. The spectral parameters indicate that the magnetic structure of manganese garnet differs slightly from the exchange triangular 120-degree structure. The anisotropy of the spin reduction and (or) weak antiferromagnetism that are allowed by the crystal symmetry lead to the difference of ≈3% in the magnetization of sublattices in the field H < H c. When the spin plane rotates from the orientation perpendicular to the C 3 axis to the orientation perpendicular to the C 4 axis, all magnetic moments of the electronic subsystem decrease by ≈2% from the average value in the zero field.  相似文献   

11.
We show that the recently proposed S = 2 bond model with orbital degrees of freedom for insulating V2O3 not only explains the anomalous magnetic ordering but also other mysteries of the magnetic phase transition. The model contains an additional orbital degree of freedom that exhibits a zero temperature quantum phase transition in the Ising universality class.  相似文献   

12.
Commensurate antiferromagnetic ordering has been observed in the superconducting high- Tc cuprate YBa2Cu3O6.5 ( Tc = 55 K) by polarized and unpolarized elastic neutron scattering. The magnetic peak intensity exhibits a marked enhancement at Tc. Zero-field muon-spin-resonance experiments demonstrate that the staggered magnetization is not truly static but fluctuates on a nanosecond time scale. These results point towards an unusual spin density wave state coexisting with superconductivity.  相似文献   

13.
The structure of Bi4?x La x Ti3O12 (BLaTx) as a function of La content from x = 0.00 to 1.25 was studied by Raman spectroscopy and X-ray diffraction (XRD). It was observed that the Raman modes evolve discontinuously at about x = 1.00, which indicates a structural phase transition. Specifically, the B 2g and B 3g Raman modes shown evidences to coalesce into E g modes with increasing La content. The evolution of Raman modes corresponds to the weakening of ferroelectric orthorhombic lattice distortion with increasing La substitution when x ≤ 1.00 and the final transition into the paraelectric tetragonal structure at higher La content. XRD and electrical measurement results confirm this phase transition by the observation that diffraction peaks from (200) and (020) planes of BLaT0.75 coalesce into one peak in BLaT1.25 and by the corresponding disappearance of remanent polarisation. The impact of La substitution on electrical properties of BLaTx is discussed briefly.  相似文献   

14.
The first-order metal-insulator transition (MIT) in paramagnetic V2O3 is studied within the ab initio scheme LDA+DMFT, which merges the local density approximation (LDA) with dynamical mean field theory (DMFT). With a fixed value of the Coulomb U=6.0 eV, we show how the abrupt pressure driven MIT is understood in a new picture: a pressure-induced decrease of the trigonal distortion within the strong correlation scenario (which is not obtained within LDA). We find good quantitative agreement with (i) switch of the orbital occupation of (a(1g),e(pi)(g1),e(pi)(g2)) and the spin state S=1 across the MIT, (ii) thermodynamics and dc resistivity, and (iii) the one-electron spectral function, within this new scenario.  相似文献   

15.
针对NiS2-xSe,系统在x=1.00附近发生的反铁磁量子相变,制备了一系列NiS2-xSex(x=0.96,0.98,1.00,1.05,1.10和1.20)多晶样品,对其结构、磁性质和电阻率进行了系统的观测.结果发现:样品磁化率-温度关系呈现典型的强关联电子系统特征;与铜氧化物超导体相类似,它们的电阻率-温度关系在很宽的温区内(50--300 K)呈现线性行为;对于x=0.98,1.00样品,低温下(3-30 K)电阻率满足p(T)∝T3/2,呈现非费米液体行为,而在x=1,10,1.20样品中的ρ(T)又呈现费米液体预言的T2关系.根据与量子相变行为相关的反铁磁量子涨落对结果进行了讨论.  相似文献   

16.
The metal-insulator (M-I) transition in vanadium sesquioxide V2O3 has been investigated by time differential perturbed angular correlation measurements of the electric fieldgradient (EFG) and the magnetic hyperfine field at dilute111Cd impurities. The EFG undergoes a first-order change at the M-I transition at Tt=160 K, but does not reflect the high temperature resistivity anomaly. The increase of the EFG with temperature in the metallic phase can be attributed to thermal variations of the oxygen sublattice. The temperature dependence of the magnetic hyperfine field in the insulating phase follows a Brioullin function with a saturation value of Hhf(O)=15 KOe and an extrapolated Neel temperature, which, depending on the impurity concentration, varies between 188 and 230 K.  相似文献   

17.
Raman scattering by phononic and electronic excitations, as well as the magnetic susceptibility of water-intercalated YBa2Cu3O6.8, has been studied. Direct evidence of the incorporation of OH?-groups into the structure of the crystal has been obtained. The observed changes in the phonon spectrum and the appearance of the spectrum of antiferromagnetic fluctuations with an increased exchange coupling constant imply the localization of carriers and suppression of superconductivity. Change in the resonance behavior of the two-magnon scattering of light indicates the transformation of the electronic structure in crystallites absorbing water.  相似文献   

18.
Garnet type solid electrolyte Li7La3Zr2O12 (LLZO) is the most promising candidate among solid electrolytes for all solid state Li batteries. In this work, small amount of Nd doping (5%–20%) to the garnet structure is proposed to improve its ionic conductivity. Nd doped garnet type solid electrolytes for Li-ion batteries were synthesized through a conventional solid state reaction method. The effect of Nd doping on the microstructure, morphology and ionic conductivity of the LLZO was studied by powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and Electrochemical impedance spectroscopy (EIS) methods. Instead of La whose valence is similar to that of Nd, XRD and Raman analyzes revealed that Nd takes the place of the higher valence element Zr. In order to compensate the valence difference, the ratio of Li increases in the structure. On the other side, results showed that Nd doped LLZO samples formed as a mixture of both tetragonal and cubic phases. According to EIS measurements, among the prepared samples, 5% Nd doped LLZO exhibits the highest ionic conductivity of 2.47 × 10−6 S cm−1 at room temperature.  相似文献   

19.
Neutron scattering measurements on the amorphous spin glass Al2Mn3Si3O12 have been made using the time-of-flight method. The scattering lawS(Q, ) reveals a quasielastic line with temperature andQ-dependent linewidth and an elastic line with constant intensity between 15 and 294K. The linewidth of the quasielastic scattering diminishes with decreasing temperature following an Arrhenius law at least down to 15K. Deviations from this exponential form are strictly correlated with an increase of the elastic intensity below 15K. We favour the opinion that this effect is caused by the instrumental resolution rather than by the onset of spin glass freezing.  相似文献   

20.
The structural phase transition from α-Rh2O3 to β-Rh2O3 has been studied via the PAC method on dilute111Cd impurity atoms implanted into α-Rh2O3. The measured antishielding factor β=112 (2) in the α-phase is similar to that found for111Cd in other oxides with corundum structure (Al2O3. Cr2O3, Fe2O3). Oxygen with different crystallographic matrices show a pronounced correlation of the electric field gradient with the NN oxygen coordination.  相似文献   

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