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Abstract:

We report a muon-spin relaxation study of the two-dimensional spin-gap system CaV4O9. We find that the form of the muon-spin relaxation is strongly temperature dependent and attribute this behaviour to the presence of a spin gap. At temperatures below 30 K a root-exponential behaviour is seen for the muon-spin relaxation function, which can be attributed to defect spins. At temperatures above 160 K we see the onset of muon hopping.

Abstract:

Experiments on three double-layer (n=2) Ruddlesden-Popper (RP) systems are reported. Doping Sr1.8La1.2Mn2O7 (Tc = 126 K) with Nd to form Sr1.8La1.2- xNdxMn2O7 leads to a reduction in Curie temperature for low doping levels (x = 0.2), and to behavior reminiscent of Sr1.8Nd1.2Mn2O7 for x≥0.7. This suggests that it may be possible to control the temperature of maximum magnetoresistance chemically in these phases. The application of pressure (0

2NdMn2O7 to resemble those of Sr 1.9Nd1.1Mn2O7. The changes can be explained by considering the relative strength of ferromagnetic and antiferromagnetic interactions within the material. Finally, the need for careful phase analysis of n = 2 RP materials is demonstrated by the misleading magnetization data recorded for a sample of Sr1.8Sm 1.2Mn2O7 containing ∼2.8% of an n = ∞ perovskite phase. © 1998 American Institute of Physics.

Abstract:

We experimentally demonstrate a mechanism for a new kind of magnetic resonance, the Fermi-surface traversal resonance (FTR). This is caused by the periodic traversal of carriers across quasi-one-dimensional (Q1D) sections of Fermi surface (FS) in an external magnetic field. Owing to the warping of the Q1D Fermi sheets, the real space velocities of the carriers oscillate as they cross the FS, generating resonances in the high frequency conductivity of the material. The results contain information about the FS, including the direction and harmonic content of the warping components. Using a rotating resonant-cavity system, FTRs have been observed in α-(BEDT-TTF)2 KHg(SCN)4. © 1998 The American Physical Society.

Abstract:

We have performed muon-spin rotation (mu SR) measurements on the organic superconductor K-(BEDT-TTF)(2)CU(SCN)(2) as a function of the angle between the applied field and the superconducting planes. The measurements are found to have much in common with those on the anisotropic cuprate superconductor Bi2Sr2CaCu2O8 divided by delta. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

A non-linear model of solid-state amorphization (SSA) is proposed which takes into account the interaction of the structural elements of the amorphous phase via a stress field. For the experimental parameters which correspond to semiconductors undergoing SSA by high-pressure phase retention, we obtain the solution in the form of a self-sustaining wave with a constant velocity v. This solution exists in the region v < vc, where the critical velocity vc is controlled by the thermal and concentration diffusivities DT and DN . A simple scaling relation is proposed for vc: vc(DN, DT) ∼ DT/(DN)0.5. It is found that the characteristic correlation length of the amorphous phase formed by SSA strongly depends on the interplay between the parameters v, DN and DT.