Magnetic Properties of X-ray Irradiated Organic Mott Insulator κ-(BEDT-TTF)₂Cu[N(CN)₂]Cl

Abstract

We have performed static magnetic susceptibility and ESR measurements on the X-ray-irradiated organic Mott insulator -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. The Néel temperature and the spin-flop transition field decrease with increasing irradiation dose. In the ESR signal at 4 K, a paramagnetic component ($15%) from itinerant carriers appears after irradiation in addition to the parent antiferromagnetic ($85%) and minor paramagnetic localized spin components. We propose that domains of the itinerant carriers with a size on the ten nanometer scale are induced around the molecular defects randomly introduced by X-ray irradiation.

Spin and Charge Transport in the X-ray Irradiated Quasi-2D Layered Compound: κ-(BEDT-TTF)2Cu[N(CN)2]Cl

“…Usually charged defects effectively increase the spin relaxation rate in conductors. The insensitivity of T 2 to irradiation and the relatively small decrease in T x are in agreement with earlier findings [9] that the concentration of induced defects is small even under the largest dose. 2 at 50 K Figure 6 displays the irradiation dependence of the ESR spectra at 222.4 GHz and the spin relaxation times.…”

“…This study follows previous optical, resistivity, static magnetization and low frequency (9 GHz) ESR measurements on irradiated κ-ET 2 -Cl [6,9] and κ-ET 2 -Br [10] crystals at Tohoku University (Sendai, Japan). The method of irradiation has been described earlier [6].…”

“…Although κ-ET 2 -Cl is a strongly correlated system and at high temperatures there are no long lifetime quasi-particles, the independence of the susceptibility and the T x /ρ ⊥ ratio indicate that the electronic structure is not strongly affected by the irradiation. The defect dose independence of T 2 , the relatively small decrease of T x at 250 K with dose and earlier magnetic measurements [9] indicate that the defect concentration is small.…”

“…It is independent of temperature and irradiation dose. (4) The magnetic spin susceptibility is approximately temperature independent and does not change with irradiation [9]. (5) The intralayer spin relaxation time T 2 is independent of temperature and dose.…”

Mott-Anderson Transition in Molecular Conductors: Influence of Randomness on Strongly Correlated Electrons in the κ-(BEDT-TTF)2X System

“…Actually, the molecular disorder introduced by X-ray irradiation to the organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 increases the residual resistivity, and suppresses the superconductivity [18,27]. We investigated the X-ray irradiation effect widely in κ-(BEDT-TTF) 2 X showing superconductivity or Mott insulating state from the viewpoint of the relation between the correlated electronic states and randomness [20,[27][28][29][30][31][32][33][34]. Recently, we found that the weak molecular disorder introduced by X-ray irradiation of the organic superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br induced the Anderson-type localization insulating state from the strongly correlated metallic/superconducting state [31].…”