arXiv subjects

B. H. Ward

Publications and source records attributed to B. H. Ward.

5 recordsLinked to original sources

arXiv2003

Experimental study of MnCl3(C12H8N2) - an S = 2 Heisenberg antiferromagnetic chain

The thermodynamic and magnetic properties of MnCl3(C12H8N2), have been studied down to 2 K. The material is an S = 2 antiferromagnetic linear chain that undergoes long-range ordering to a canted antiferromagnetic state at 23 K. The comparison of magnetic data from polycrystalline samples with the results of specific heat measurements using a pressed pellet of powder reveals the importance of the length of the chains in the sample in relation to the magnetic correlation length.

cond-mat.soft↗

arXiv2003

High field magnetic resonant properties of beta'-(ET)2SF5CF2SO3

A systematic electron spin resonance (ESR) investigation of the low temperature regime for the (ET)2SF5CF2SO3 system was performed in the frequency range of ~200-700 GHz, using backward wave oscillator sources, and at fields up to 25 T. Newly acquired access to the high frequency and fields shows experimental ESR results in agreement with the nuclear magnetic resonance (NMR) investigation, revealing evidence that the transition seen at 20 K is not of conventional spin-Peierls order. A significant change of the spin resonance spectrum in beta'-(ET)2SF5CF2SO3 at low temperatures, indicates a transition into a three-dimensional-antiferromagnetic (3D AFM) phase.

cond-mat.mtrl-sci↗

arXiv2000

Electronic Structure of Novel Cation-Radical Salts in High Magnetic Fields

Two organic conducting materials, where unusual aspects of their composition play important roles, are explored: beta''-(BEDT-TTF)2SF5XSO3 which exhibits superconductivity, or a metal-insulator transition (for X=CH2CF2 or CHF respectively), and tau-(P-S, S -DMEDT-TTF)2 (AuBr2) (AuBr2)y which exhibits a large, hysteretic, negative magnetoresistance. Detailed angular dependent magnetoresistance studies that allow a tomographic view of the electronic structure of these materials with increasing magnetic fields are presented.

cond-mat.str-el↗

arXiv1998

Magnetic Studies of End-Chain Spin Effects in the Haldane Gap Material Ni(C3H10N2)2N3(ClO4)

Electron spin resonance (ESR), at 9, 94, and 190 GHz, and magnetization studies on polycrystalline, powder, and ultrafine powder samples of Ni(C3H10N2)2N3(ClO4) (NINAZ) have revealed several effects arising from the Haldane phase. Using the g value of the end-chain spin $S$ as determined by ESR, our results confirm that the end-chain spins are S=1/2 and show no evidence for S=1 end-chains. In addition, the ESR signals reveal spectral weight consistent with a model describing interactions between the end-chain spins on the shortest chains and between the magnetic excitations on the chains and the end-chain spins.

cond-mat.str-el↗

arXiv1997

Experimental Evidence of a Haldane Gap in an S = 2 Quasi-linear Chain Antiferromagnet

The magnetic susceptibility of the $S = 2$ quasi-linear chain Heisenberg antiferromagnet (2,$2'$-bipyridine)trichloromanganese(III), MnCl_{3}(bipy), has been measured from 1.8 to 300 K with the magnetic field, H, parallel and perpendicular to the chains. The analyzed data yield $g\approx 2$ and $J\approx 35$ K. The magnetization, M, has been studied at 30 mK and 1.4 K in H up to 16 T. No evidence of long-range order is observed. Depending on crystal orientation, $M\approx 0$ at 30 mK until a critical field is achieved ($H_{c\|} = 1.2\pm 0.2 T$ and $H_{c\bot} = 1.8\pm 0.2 T), where M increases continuously as H is increased. These results are interpreted as evidence of a Haldane gap.

cond-mat.str-el↗