共查询到10条相似文献,搜索用时 62 毫秒
1.
Helme LM Boothroyd AT Coldea R Prabhakaran D Tennant DA Hiess A Kulda J 《Physical review letters》2005,94(15):157206
We report polarized- and unpolarized-neutron scattering measurements of magnetic excitations in single-crystal Na0.75CoO2. The data confirm ferromagnetic correlations within the cobalt layers and reveal antiferromagnetic correlations perpendicular to the layers, consistent with an A-type antiferromagnetic ordering. The magnetic modes propagating perpendicular to the layers are sharp, and reach a maximum energy of approximately 12 meV. From a minimal spin-wave model, containing only nearest-neighbor Heisenberg exchange interactions, we estimate the interlayer and intralayer exchange constants to be 12.2+/-0.5 meV and -6+/-2 meV, respectively. We conclude that the magnetic fluctuations in Na0.75CoO2 are highly three dimensional. 相似文献
2.
Geck J von Zimmermann M Berger H Borisenko SV Eschrig H Koepernik K Knupfer M Büchner B 《Physical review letters》2006,97(10):106403
We present a combined high-energy x-ray diffraction and local-density approximation study of the sodium ordering in Na(0.75)CoO2. The obtained results rule out previously proposed Na-ordering models and provide strong evidence for the formation of sodium-density stripes in this material. The local-density approximation calculations prove that the sodium-density stripes lead to a sizable dip in the density of the Co states at the Fermi level, pointing to band structure effects as a driving force for the stripe formation. This indicates that the sodium ordering is connected to stripelike charge correlations within the CoO2 layers, leading to an astonishing similarity between the doped cuprates and the NaxCoO2 compounds. 相似文献
3.
Bernhard C Boris AV Kovaleva NN Khaliullin G Pimenov AV Yu L Chen DP Lin CT Keimer B 《Physical review letters》2004,93(16):167003
Using spectral ellipsometry, we measured the dielectric function of a Na(0.82(2))CoO2 crystal that exhibits bulk antiferromagnetism with T(N)=19.8 K. We identify two prominent transitions as a function of temperature. The first one at 280 K involves marked changes of the electronic and lattice responses that are indicative of charge ordering in the CoO2 layers. The second transition occurs around T(N)=19.8 K and reveals sizable spin-charge coupling. The data are discussed in terms of charge ordering and formation of magnetopolarons due to a charge-induced spin-state transition of adjacent Co3+ ions. 相似文献
4.
We report the magnetization, specific heat, and transport measurements of a high quality Na(0.85)CoO2 single crystal in applied magnetic fields up to 14 T. At high temperatures, the system is in a paramagnetic phase. It undergoes a magnetic phase transition below approximately 20 K. For the field H||c, the measurement data of magnetization, specific heat, and magnetoresistance reveal a metamagnetic transition from an antiferromagnetic state to a quasiferromagnetic state at about 8 T at low temperatures. However, no transition is observed in the magnetization measurements up to 14 T for H perpendicular c. The low temperature magnetic phase diagram of Na(0.85)CoO2 is determined. 相似文献
5.
Bayrakci SP Mirebeau I Bourges P Sidis Y Enderle M Mesot J Chen DP Lin CT Keimer B 《Physical review letters》2005,94(15):157205
NaxCoO2, the parent compound of the recently synthesized superconductor Na(x)CoO(2):yH(2)O, exhibits bulk antiferromagnetic order below approximately 20 K for 0.75=x=0.9. We have performed neutron scattering experiments in which we observed Bragg reflections corresponding to A-type antiferromagnetic order in a Na0.82CoO2 single crystal and characterized the corresponding spin-wave dispersions. The spin waves exhibit a strongly energy-dependent linewidth. The in-plane and out-of-plane exchange constants resulting from a fit to a nearest-neighbor Heisenberg model are similar in magnitude, which is unexpected in view of the layered crystal structure of NaxCoO2. Possible implications of these observations are discussed. 相似文献
6.
Julien MH de Vaulx C Mayaffre H Berthier C Horvatić M Simonet V Wooldridge J Balakrishnan G Lees MR Chen DP Lin CT Lejay P 《Physical review letters》2008,100(9):096405
From 59Co and 23Na NMR, we demonstrate the impact of the Na+ vacancy ordering on the cobalt electronic states in Na0.75CoO2: at long time scales, there is neither a disproportionation into 75% Co3+ and 25% Co4+ states, nor a mixed-valence metal with a uniform Co3.25+ state. Instead, the system adopts an intermediate configuration in which 30% of the lattice sites form an ordered pattern of localized Co3+ states. Above 180 K, an anomalous mobility of specific Na+ sites is found to coexist with this electronic texture, suggesting that the formation of the latter may contribute to stabilizing the Na+ ordering. Control of the ion doping in these materials thus appears to be crucial for fine-tuning of their thermoelectric properties. 相似文献
7.
We report polarized and unpolarized neutron scattering measurements of the magnetic order in single crystals of Na0.5CoO2. Our data indicate that below TN=88 K the spins form a novel antiferromagnetic pattern within the CoO2 planes, consisting of alternating rows of ordered and nonordered Co ions. The domains of magnetic order appear to be closely coupled to the domains of Na ion order, consistent with such a twofold symmetric spin arrangement. Magnetoresistance and anisotropic susceptibility measurements further support this model for the electronic ground state. 相似文献
8.
Li SY Taillefer L Hawthorn DG Tanatar MA Paglione J Sutherland M Hill RW Wang CH Chen XH 《Physical review letters》2004,93(5):056401
The in-plane resistivity rho and thermal conductivity kappa of single crystal Na0.7CoO2 were measured down to 40 mK. Verification of the Wiedemann-Franz law, kappa/T=L(0)/rho as T-->0, and observation of a T2 dependence of rho at low temperature establish the existence of a well-defined Fermi-liquid state. The measured value of coefficient A reveals enormous electron-electron scattering, characterized by the largest Kadowaki-Woods ratio A/gamma(2) encountered in any material. The rapid suppression of A with magnetic field suggests a possible proximity to a magnetic quantum critical point. We also speculate on the possible role of magnetic frustration and proximity to a Mott insulator. 相似文献
9.
Balicas L Analytis JG Jo YJ Storr K Zandbergen H Xin Y Hussey NE Chou FC Lee PA 《Physical review letters》2006,97(12):126401
Shubnikov-de Haas oscillations for two well-defined frequencies, corresponding, respectively, to areas of 0.8 and 1.36% of the first Brillouin zone, were observed in single crystals of Na(0.3)CoO2. The existence of Na superstructures in Na0.3CoO2, coupled with this observation, suggests the possibility that the periods are due to the reconstruction of the large Fermi surface around the Gamma point. An alternative interpretation in terms of the long sought-after epsilon'(g) pockets is also considered but found to be incompatible with existing specific heat data. 相似文献
10.
L. Yu Y. Wang H.-U. Habermeier 《Applied Physics A: Materials Science & Processing》2013,112(3):569-573
AZO thin films with low surface roughness and low sheet resistance are required in the touch panels and display panels. In this work, we investigated the substrate cooling effect of the ion beam post-treatment on AZO films properties, and one new way to obtain low surface roughness and low sheet resistance at the same time was proposed. The more exciting find of this paper is that, compared to the samples without cooling during the process of the ion beam post-treatment, samples with proper cooling voltage show a sheet resistance decrease of 26 % (from 11.9 Ω/□ to 8.8 Ω/□) and a roughness decrease of 35.5 % (from 13.389 nm to 8.637 nm) without transparency losing. And the viewpoint that substrate cooling has the effect of weakening the crystallization, especially for the subface and internal parts of samples is deduced. 相似文献