Muons and magnets

Abstract:

We present a model of a quasi-one-dimensional (Q1D) conductor with weak dispersion in the direction perpendicular to the chains in a magnetic field. Finite-energy electric dipole transitions between the eigenstates of the system constitute Fermi-surface traversal resonance, a Q1D analogue of cyclotron resonance. We extend the model to describe a (TMTSF)(2)X-like material, with dispersion in two directions perpendicular to the chains, and find that for certain orientations of the magnetic field large degeneracies occur between the magnetic-field induced states. These are angles at which maxima are observed experimentally in the d.c. conductivity, and thus we explain one class of angle-dependent magnetoresistance oscillations (AMRO) in terms of zero-energy electric dipole transitions between magnetic-field induced states.

Abstract:

We present the field dependent magnetization and magnetic susceptibility of an unusual metamagnet Co-2(OH)(2)(O2CC6H4CO2). It is characterized by a maximum in the susceptibility at the Neel temperature of 48 K and by spontaneous magnetization at a T-C of 43 K due to a small canting. It displays the characteristic kink of a metamagnetic transition in the field-dependent magnetization below T-N. Below T-C hysteresis is observed whose width increases to span +/- 5.2 T at 1.5 K. We propose a qualitative explanation of the rich phase behaviour.

Abstract:

Magnetic properties of purely organic radical ion salts and complexes based on nitronyl nitroxide (NN) derivatives were investigated. The salts and complexes are composed of N-alkylareniumyl NN as the radical cations and carboxylatoaryl, sulfonatoaryl and imidazolidyl NN as the radical anions. Tetracyanoquinodimethanide (TCNQ)(-) salts and complexes were also prepared. The results obtained for several complexes of a multifunctional molecule, 2-imidazoly NN (2-IMNN), are presented in detail, because 2-IMNN can be converted to various with p-carboxylatophenyl NN states by electron and proton transfers. The proton-transfer complex of 2-imidazoliniumyl NN (2-IMNN)(+*) with (p-CAPNN)(-*) shows magnetic behavior relevant to coexistence of intermolecular ferro- and antiferro-magnetic interactions. Several quinoliniumyl NN(QNNN)(+*)(p-CAPNN)(-*) complexes exhibit magnetic behavior similar to that observed in (2-IMNN)(+*)(p-CAPNN)(-*).

Abstract:

Muon-spin relaxation (mu SR) experiments on the conducting polymer poly(2,3-dibutoxy-1,4-phenylene vinylene) (DB-PPV) probe the dynamics of the highly mobile polarons created by the muon-implantation process in which muonium reacts with the polymer forming a radical state. The fluctuating spin density induced by the electronic spin defect rapidly diffusing up and down the chain leads to a characteristic relaxation, the temperature and field dependence of which permit the extraction of on-chain and inter-chain diffusion rates. These results provide information concerning: the charge-transport mechanism in DB-PPV.

Abstract:

We present a numerical simulation of angle dependent magnetoresistances oscillations(AMROs) in alpha-(BEDT-TTF)(2)KHg(SCN)(4). The nesting vector of the density wave and the magnetic breakdowngap in the low-temperature, low-magnetic-field state (LTLF) are constrained by simulations of quasi-one-dimensional (Q1D) AMRO. Quasi-two-dimensional (Q2D) AMRO simulations for the high-temperature, high-magnetic-field state (HTHF) allow the precise derivation of an ellipticity of the Q2D Fermi surface. Simulations of the field dependent AMRO demonstrate the gradual evolution of the FS from LTLF to HTHF states toward the kink transition at 23 T.