Anomalous Diamagnetism Research Articles

Superconducting fluctuations and anomalous diamagnetism in underdopedYBa2Cu3O6+xfrom magnetization and63CuNMR-NQR relaxation measurements

Magnetization and 63Cu NMR-NQR relaxation measurements are used to study the superconducting fluctuations in YBa2Cu3O6+x (YBCO) oriented powders. In optimally doped YBCO the fluctuating negative magnetization M_{fl}(H,T) is rather well described by an anisotropic Ginzburg-Landau (GL) functional and the curves M_{fl}/sqrt{H} cross at Tc. In underdoped YBCO, instead, over a wide temperature range an anomalous diamagnetism is observed, stronger than in the optimally doped compound by about an order of magnitude. The field and temperature dependences of M_{fl} cannot be described either by an anisotropic GL functional or on the basis of scaling arguments. The anomalous diamagnetism is more pronounced in samples with a defined order in the Cu(1)O chains. The 63Cu(2) relaxation rate shows little, if any, field dependence in the vicinity of the transition temperature Tc(H=0). It is argued how the results in the underdoped compounds can be accounted for by the presence of charge inhomogeneities, favoured by chains ordering.

Fluctuation Effects and Anomalous Diamagnetism in YBCO124 and in Underdoped YBCO123 from Susceptibility and 63Cu Nuclear Relaxation

The effects of superconducting fluctuations on the diamagnetic susceptibility and on the dynamical spin susceptibility involved in 63 Cu NMR-NQR relaxation rate are investigated in oriented powders of underdoped YBCO123 and of YBCO124 and compared with the ones in optimally doped YBCO123. While in this latter compound the fluctuation diamagnetism is well described by an anisotropic Ginzburg–Landau (GL) functional, in underdoped YBCO123 an anomalous diamagnetism is observed, with a strong enhancement of the susceptibility, in a wide temperature range. The magnetization curves cannot be described by any GL anisotropic functional. Also in YBCO124 the fluctuation diamagnetism is hard to describe by GL-type approach, although the enhancement is not as marked as in underdoped YBCO123. In YBCO124, and in underdoped YBCO123, the temperature and field dependences of the 63 Cu relaxation rates W appear different from the ones in underdoped YBCO123. No field-induced decrease of W is observed, as it is expected in the case of a changeover from s to d of the orbital simmetry of the fluctuating pairs or when the character of the fluctuations is different from the GL one.

Anomalous magnetic properties of plastically deformed sintered poly-and monocrystalline molybdenum

The field dependency of the magnetic susceptibility of molybdenum subjected to intensive deformation was investigated. It was found that a nonlinear increase of paramagnetism occurs in mono- and polycrystalline specimens at fields >100 Oe, but anomalous diamagnetism appears at low fields. At the same time, no unusual diamagnetic or paramagnetic effects were displayed by powder.

Magnetic studies of some orthovanadates.

The perovskites L${\mathrm{VO}}_{3}$ (L=La, Lu, or Y) are canted-spin antiferromagnets. Magnetic susceptibility measurements made on cooling from room temperature in a field of 1 kOe or on heating after cooling in 1 kOe give rise to a sample magnetization M that is oriented in opposition to the magnetizing field below 138 K in ${\mathrm{LaVO}}_{3}$, but in the direction of the magnetizing field in ${\mathrm{LuVO}}_{3}$ and ${\mathrm{YVO}}_{3}$. Orientation of the M in ${\mathrm{LaVO}}_{3}$ in opposition to the magnetizing field H occurs on cooling through a first-order magneto- strictive transition at 138 K${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}142 K that enhances the ${\mathit{V}}^{3+}$ ion orbital angular momentum. In ${\mathrm{YVO}}_{3}$, a first-order magnetic-order phase change at 78 K ${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}114 K shows no evidence of a discontinuous change in the ${\mathrm{V}}^{3+}$ ion orbital angular momentum. The same is true for a phase change in ${\mathrm{LuVO}}_{3}$ at 83 K${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}105 K that leaves the magnetic order unchanged. A high-pressure (P\ensuremath{\ge}8 kbar) ${\mathrm{LaVO}}_{3}$ phase metastable below 250 \ifmmode^\circ\else\textdegree\fi{}C is antiferromagnetic without spin canting. The ``anomalous diamagnetism'' previously reported for field-cooled ${\mathrm{LaVO}}_{3}$ is interpreted to reflect the first observation of a change in the direction of the persistent currents at an ion associated with a discontinuous change in an unquenched orbital angular momentum contribution to the atomic moment; a spin-orbit coupling stronger than the Zeemann coupling of the spin to the magnetizing field reverses the entire atomic moment ${\mathrm{\ensuremath{\mu}}}_{\mathit{J}}$=gJ${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. Substitution of La by Lu or Y applies a chemical pressure that suppresses the first-order magnetostrictive distortion responsible for the anomalous diamagnetism.

Antiferromagnetic Nuclear Resonance of51V in LaVO3and YVO3

We have investigated the antiferromagnetic nuclear magnetic resonance (AFNR) of 51 V in perovskites LaVO 3 and YVO 3 under zero external magnetic field. In LaVO 3 , two distinct resonance lines are observed around 261.90±0.05 MHz and 268.98±0.05 MHz at 4.2 K. These signals are associated with the inequivalent 51 V sites generated by the structural transition at T N . The Larmor frequencies at the inequivalent sites are found to show different temperature dependences. This clearly indicates that the temperature dependence of the sublattice magnetization is different for each site, and may be related to the anomalous diamagnetism of this compound. The resonance line is observed around 278.8±0.1 MHz at 4.2 K in YVO 3 . The hyperfine coupling constants of both substances are also estimated.

Anomalous diamagnetism at the twinning plane

The twin in magnetic field parallel to the twinning plane is considered In weak fields the surface diamagnetic susceptibility diverges as inverse squared magnetic field. Such behavior of susceptibility leads instability and resultsin formation of diamagnetic domain at the twinning pane.

Anomalous diamagnetism at the twinning plane

The twin in magnetic field parallel to the twinning plane is considered In weak fields the surface diamagnetic susceptibility diverges as inverse squared magnetic field. Such behavior of susceptibility leads instability and resultsin formation of diamagnetic domain at the twinning pane.

Effects of viscosity on plasma equilibria

High-beta large ion-gyroradius plasmas in the University of Wisconsin Octupole [Phys. Rev. Lett. 46, 1394 (1981)] exhibited an anomalous diamagnetism that is smaller than the prediction from ideal magnetohydrodynamic (MHD) theory by a factor of up to 5. The effects of viscosity on the equilibrium diamagnetism are presented and shown to be qualitatively consistent with the experimental results.

General properties of electromagnetic response functions

The present state of the general theory of response functions of material media, describing the universal properties of these functions that characterize all types of medium, is surveyed. Topics covered include recent results on the range of admissible values of static permeability, the form of the Landau functional for the electrodynamic ordering of a medium, and the electrodynamics of a medium interacting with a magnetic monopole. Applications to high-temperature superconductivity, anomalous diamagnetism, and monopole detection are discussed.

Review of two models of superconduction behavior in CuCL and CdS

In this review, we shall briefly discuss two models which help explain the anomalous diamagnetism and paramagnetism in CuCl and CdS at temperatures above that of liquid nitrogen. These models are built around there being some form of a superconducting phase in these materials. The first model is an optical phonon mediated electron-interaction developed by Bishop and Overhauser1, and the second model developed by Collins et al.2.3 is the outgrowth of the work of Little4, Devreese et al.5 This model includes the use of literature concerning He3 p, -states6 and is built around calculated band structures and the polarization of the valence band by conduction electrons at moderately high impurity concentrations.

Evidence for photoactivated defect induced dielectric anomalies in CuCL

Dielectric measurements of optically irradiated single crystal and composite samples of CuCl prepared and stored under carefully controlled conditions have revealed anomalies in both the capacitance and tan δ at 220 K. At low temperature the capacitance shows a peak versus increasing integrated photon flux which is interpreted as increasing photoinduced Cu° defect precipitate. The results are reproducible and correlate with earlier reports of anomalous diamagnetism (high temperature superconductivity precursor) in CuCl. The observation of a large low frequency dielectric constant in CuCl supports the existence of a low frequency (soft) phonon mode in the CuCl-Cu precipitate composite which could provide a mechanism for high temperature superconductivity.

Localized lattice instability in zinc-blende semiconductors: Microscopic model for large lattice relaxation and for high-temperature anomalous diamagnetism

Based on the structural properties of the zinc-blende lattice, a model Hamiltonian is proposed to describe singly and doubly occupied impurity states with large lattice relaxation. One-electron impurity levels are proposed to be connected with the anomalous persistent free-particle excitations. The impurity band of the bound pair states might show Bose condensation and superconducting properties at high temperature. Combined with available band-structure data, the metastability and other properties of this model are discussed.

Anomalous magnetism of small metallic clusters in a weak magnetic field

Anomalous diamagnetism in small magnetic fields may be observed in systems consisting of size-quantized metallic clusters. With the increase of magnetic field the diamagnetic susceptibility decreases until ordinary values χ 0 ∼ 10 -5 -10 -6. The conditions for the existence of anomalous paramagnetism and orbital ferromagnetism in such systems are also discussed. An increase of the diamagnetic susceptibility in anisotropic semiconductors due to impurities is predicted.

Thermal and structural analysis of the effects of chlorine impurities on pressurized CdS

Anomalous large diamagnetism (χv∼−0.25/4π cgs units) and large positive magnetism (χv∼+10−4 cgs units) have recently been reported in pressure-quenched CdS polycrystalline samples by Homan and MacCrone. These effects were shown to be sample material source dependent, and as a first step toward characterizing these samples, we compared the thermal and structural properties of various CdS samples before and after pressurization. Samples containing up to 6-wt. % Cl were prepared by precipitaion from a chloride containing aqueous bath. We find that (i) Cl impurities are probably present in the form of a complex which can decompose on heating to CdS+CdCl2, (ii) melting of a portion of the samples containing high levels of Cl occurs at 535 °C and is attributed to the eutectic temperature of the CdS+CdCl2 mixture, and (iii) heating beyond 535 °C produces complete volatization of the CdCl2 component. The results on samples prepared by mixing of CdS and CdCl2⋅H20 were examined and found to have similar thermal behavior. The cadmium sulfide used in the previous magnetization study was examined and, based on the similarities in the thermal and structural properties, we conclude that the samples which exhibit the anomalous magnetic effects were also prepared by precipitation. In agreement with earlier studies, metastable phases are observed after various pressurizations to above 4.0 GPa.

A piezoelectric hypothesis for interface superconductivity in CuCl

A new model for “excitonic” superconductivity is proposed to explain the anomalous diamagnetism seen in CuCl. The superconductivity is presumed to occur in thin layers of copper deposited in grain boundaries of the CuCl. Pairing of the cooper electrons is ascribed to virtual electronic excitations between the metal and adjacent, two-dimensional potential minima in the CuCl resulting from the piezoelectric polarization due to the elastic strain of grain boundry dislocations.

Effects related to pair correlation of π electrons

A good deal has been written about correlation effects of electrons in molecules. We consider a somewhat special type of correlation, viz., the pair correlation of π electrons in large molecules. Various attraction mechanisms which lead to this correlation are discussed. We study the behavior of the large π electron systems in external electric and magnetic fields (i.e., anomalous diamagnetism, polarizability, analog to the Kirkwood formula). It has been shown that in a strong magnetic field pair correlation leads to an additional reduction of the magnitude of the 0–0′ transition. We also consider collective excitations and multiplet structure of the π electron spectrum.

Impurity Diamagnetism in Metals

The results of a broad experimental survey of impurity magnetism in liquid monovalent metal solvents is reported. As the impurity valence $Z$ is increased, a giant impurity diamagnetism \ensuremath{\sim} - 150 ${\mathrm{cm}}^{3}$/mole emerges in alkali-metal solvents for $Z$ \ensuremath{\sim} 5. The diamagnetism is explained by the concept of impurity ionicity developed in this paper, and the impurity structure is analyzed in detail using the present results and earlier spin-flip-scattering results of Slichter and his co-workers. There is quantitative agreement between the theory of fully ionic impurities and the experimental susceptibilities for higher-valence impurities. The broad scheme of impurity structure in monovalent metals is also clearly revealed. The susceptibility of Sn is studied as a function of host-electron density, and the transition from band to resonant $5p$ orbitals is identified. A solubility dip occurs, but the data are not precise enough to determine whether the transition has a one-electron or configurational character. It is further reported that the large diamagnetism of positive-valence solutes in Ag, previously studied by Henry and Rogers, disappears at the melting transition. No detailed analysis of this striking effect has been attempted, but the anomalous impurity diamagnetism in the solid is clearly associated with orbits involving the [111] necks on the Fermi surface.

Influence of Chemical Golloidisation on the Anomalous Diamagnetism of Bismuth and Antimony

IT is a well-known fact that antimony and bismuth possess a high diamagnetism in the solid massive state, the specific susceptibilities being 0.78 × 10−6 and 1.17 × 10−6 respectively at 30° C. according to my experiments. In a communication published in NATURE of Nov. 16, 1929, p. 762, I reported the results of the influence of particle size on the anomalous diamagnetism of antimony, its value falling on mechanical colloidalisation. Further experiments on chemical colloids of bismuth and antimony show a still more striking decrease.