Muons and magnets

Abstract:

We have performed detailed studies of the angle- and temperature-dependent resistive upper critical fields in the layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2. With the magnetic field lying in the conducting planes, our measurements show an upper critical field which comfortably exceeds the Pauli-paramagnetic limit in this material. We find no azimuthal angle dependence of the critical field, in spite of recent evidence that this material has gap nodes characteristic of d-wave superconductivity. We propose that the large critical fields may be due to a Fulde-Ferrell-Larkin-Ovchinnikov state which can exist in exactly in-plane fields because of the nature of the Fermi surface of κ-(BEDT-TTF)2Cu(NCS)2. © 1999 IOP Publishing Ltd.

Abstract:

Muon-spin rotation (μSR) measurements have been used to study the vortex lattice and its instabilities in the organic superconductors κET2Cu(SCN)2 and βET2IBr2. We ascribe the field- and temperature-dependent destruction of the vortex lattice to the large anisotropy found in these materials.

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 alpha-(BEDT-TTF)(2)KHg(SCN)(4).

Abstract:

We have carried out magnetic measurements on the layered magnets Ni-2(OH)(3)(N(CN)(2)) (NiAM), Co-5 (OH)(8)(N(CN)(2))(2). 6H(2)O (CoAM), Co-5(OH)(8) (C12H25SO4)(2). 2NH(3) (CoDOS), and Co-5 (OH)(8) (C7H15CO2)(2). 4H(2)O ( CoCAP), using various experimental methods, including muon spin relaxation (mu SR). We find phase transitions at temperatures T-M in all the samples, characterized by a change in the magnetic susceptibilty and loss of initial muon spin polarization.