A current of electrons traversing a landscape of localized spins possessing non-coplanar magnetic order gains a geometrical (Berry) phase, which can lead to a Hall voltage independent of the ...spin-orbit coupling within the material-a geometrical Hall effect. Here we show that the highly correlated metal UCu(5) possesses an unusually large controllable geometrical Hall effect at T<1.2 K due to its frustration-induced magnetic order. The magnitude of the Hall response exceeds 20% of the ν=1 quantum Hall effect per atomic layer, which translates into an effective magnetic field of several hundred Tesla acting on the electrons. The existence of such a large geometric Hall response in UCu(5) opens a new field of enquiry into the importance of the role of frustration in highly correlated electron materials.
We report on specific heat and resistivity measurements under hydrostatic pressure on the quasi-one dimensional metal TlxV6S8. We studied the interplay between the low temperature superconducting ...(SC) ground state and a high temperature charge density wave (CDW) instability. We observed a clear dependency of the physical properties of TlxV6S8 on the Tl concentration x. The CDW anomaly is present in all investigated samples that are strongly enhanced at half Tl filling, x = 0.47. This is also the only composition for which no signature of superconductivity is observed. The specific heat results regarding the SC phase in Tl0.63V6S8 suggest that this compound is a highly anisotropic, weak coupling superconductor. Pressure suppresses both SC and CDW transitions to lower temperatures. Nevertheless, as the CDW gap is closed at a critical pressure pc, the increase in the density of states leads to a small enhancement of Tc suggesting that SC and CDW compete for parts of the Fermi-surface.
In the present investigation we studied the effect of lead content on a hard type ceramics starting from lack to excess PbO. Specimens of Pb
x
(Mn
0.017Sb
0.033Zr
0.48Ti
0.47)O
3 with 0.96
≤
x
≤
1.06 ...were prepared by conventional oxide mixing technique and sintered at temperatures between 1280 and 1350
°C. In samples with lower Pb concentration the pyrochlore phase appeared, while in those with higher Pb an excess of PbO phase was detected. These phases proved detrimental for the properties of sintered ceramics. The highest values of piezoelectric properties were observed only for samples with an excess lead of about 2% sintered at 1340
°C, indicating that it represents the optimum amount of PbO. For such samples, the density
ρ was 7.77
g/cm
3, the remnant polarization
P
r was 37
μC/cm
3 the planar coupling coefficient
k
p was 0.57 and the charge constant
d
33 was 340
pC/N.
Electronic inhomogeneity in a Kondo lattice Bauer, E. D.; Yang, Yi-feng; Capan, C. ...
Proceedings of the National Academy of Sciences - PNAS,
04/2011, Letnik:
108, Številka:
17
Journal Article
Recenzirano
Odprti dostop
Inhomogeneous electronic states resulting from entangled spin, charge, and lattice degrees of freedom are hallmarks of strongly correlated electron materials; such behavior has been observed in many ...classes of d-electron materials, including the high-Tc copperoxide superconductors, manganites, and most recently the ironpnictide superconductors. The complexity generated by competing phases in these materials constitutes a considerable theoretical challenge—one that still defies a complete description. Here, we report a manifestation of electronic inhomogeneity in a strongly correlated f-electron system, using CeColn₅ as an example. A thermodynamic analysis of its superconductivity, combined with nuclear quadrupole resonance measurements, shows that nonmagnetic impurities (Y, La, Yb, Th, Hg, and Sn) locally suppress unconventional superconductivity, generating an inhomogeneous electronic "Swiss cheese" due to disrupted periodicity of the Kondo lattice. Our analysis may be generalized to include related systems, suggesting that electronic inhomogeneity should be considered broadly in Kondo lattice materials.
Pressure studies of the thermodynamics of CeCoIn5 under magnetic fields H parallel to c and H parallel to ab have been made up to P = 1.34 GPa. We recorded the signature of the ...Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state for all pressures when H parallel to ab. Also remarkably, the FFLO regime suddenly expands for P = 1.34 GPa. With the help of a microscopic theory for d-wave superconductivity, we have extracted the gyromagnetic ratio g and the Fermi velocities nu(a) and nu(c). Our study is the first evidence for the existence of the FFLO state away from the influence of the antiferromagnetic fluctuations. We find a close parallel between the T-P phase diagram of CeCoIn5 and the T-x phase diagram of the high-Tc cuprates, where x is the hole concentration.
Soft ferrites in the CuZnTi system, having the formula Cu
1−
x
Zn
x
Ti
y
Fe
2−
y
O
4, with 0.50⩽
x⩽0.60 and 0.00⩽
y⩽0.05 were investigated as a function of composition, sintering temperature and ...cooling speed, in order to obtain materials with controlled
T
C and very high change rate of permeability with temperature around their
T
C. The effect of Zn and Ti additions was a drastic change of the Curie temperature with about 10–12
°C for each atomic percent of Zn and Ti introduced into the spinel lattice while the cooling speed changed the behaviour of magnetic permeability with temperature around the Curie point. An application using such magnetic temperature sensors for a thermostat is presented.
Nanocrystalline powders of a soft FeNbLi-doped PZT material have been prepared by a novel mechanochemical process consisting of mixing the stoichiometric oxides in a planetary ball mill for prolonged ...times up to 80 h. The constituent oxides were reacted in a tungsten carbide vial with balls of 5, 10 and 20 mm in diameter and a ball/powder ratio of 15/1. The chemical reaction between the component oxides was triggered after 20 h of energetic milling and was completed after 80 h. The XRD of the reacted nanopowder showed the well known perovskite structure. Compacted samples of this powder were sintered between 800-1300DGC for 3 h and the main piezoelectric properties were determined. The density of the sintered samples reached nearly 99% of the theoretical density at 1100DGC and showed good piezoelectric characteristics: planar coupling factor of 0.66, dielectric displacement constant d33 of 550 pmN, mechanical quality factor of 85, and relative dielectric constant of 3800. The possible mechanisms for solid state reaction of mechanically activated nanopowders such as local heating and pressure at collision as well as defects diffusion are discussed.
Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic ...technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)1-0.015-xMn0.015Sbx)O3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.
We study the ternary clathrate Pr3Pd20Si6 in specific heat and ac susceptibility measurements on a high-quality single crystal, distinguishing antiferromagnetic and antiferroquadrupolar ordering, as ...well as a hitherto unknown magnetic low-temperature transition. The specific heat shows the direct involvement of nuclear spin degrees of freedom in the antiferromagnetic ordering, which is well supported by our calculation of the hyperfine level scheme without adjustable parameters. Pr3Pd20Si6 is, therefore, one of the rare materials where the nuclear moments are involved in the formation of the magnetic ground state.
Functionally graded materials represent a new class of composite type materials characterized by a continuous variation of properties through the thickness direction. Due to this they found numerous ...applications in aerospace, automobile, biomedical or nuclear industries. Bilayered structures made from typically hard and typically soft PZT type materials as well as plain hard and soft and intimately mixed hard and soft samples were prepared by green pressed powders followed by sintering at different temperatures between 1000 and 1300°C. The dielectric and piezoelectric properties of sintered compacts were determined in relation with the nature of the interdiffusion layer involved. Electron microscopy as well as X-Ray diffractometry was used to get an insight into the interfacial diffusion process. The composition and the width of the interdiffusion layer depend on temperature. The mechanism of the interdiffusion layer and materials properties were discussed in terms of the ionic diffusion coefficients and activation energies of the species which take place into the diffusion process.
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