Magnetic ordering of defects in a molecular spin-Peierls system

Abstract

With interest in charge transfer compounds growing steadily, it is important to understand all aspects of the underlying physics of these systems, including the properties of the defects and interfaces that are universally present in actual experimental systems. For the study of these defects and their interactions a spin-Peierls (SP) system provides a useful testing ground. This work presents an investigation within the SP phase of potassium TCNQF 4 where anomalous features are observed in both the magnetic susceptibility and ESR spectra for temperatures between 60 K and 100 K. Muon spin spectroscopy measurements confirm the presence of these anomalous magnetic features, with low temperature zero-field data exhibiting the damped oscillatory form that is a characteristic signature of static magnetic order. This ordering is most likely due to the interaction between structurally correlated magnetic defects in the system. The critical behaviour of the temperature dependent muon spin rotation frequency indicates that a 2D Ising model is applicable to the magnetic ordering of these defects. We show that these observations can be explained by a simple model in which the magnetic defects are located at stacking faults, which provide them with a 2D structural framework to constrain their interactions.

Tuneability and criticality in a three-dimensional stacked molecular system

“…In TCNQ if one assumes a stopping site close to the nitrogen groups on one end where the radical electron density resides, then there is coupling to both the nitrogen and protons, if you swap the protons for fluorines then this will change the field distribution at the muon site. Coupled to the fact that there may multiple muon stopping sites, this may be especially complicated given that in the fluorinated compounds you have small contributions of F-μ + -F states [39]. This will be discussed further in a subsequent paper, but within this work it need not be focused on.…”

Driving a Molecular Spin-Peierls System into a Short Range Ordered State through Chemical Substitution

“…Although the SP state is expected to be quasi-1D, the magnetic fluctuations follow the critical power-law expected for a 3D Heisenberg system; therefore, these types of systems exhibit strongly correlated 3D behaviour. Additionally, further work also illustrated that the highly concentrated defect states can separately order, where within KTCNQF 4 , these states were suggestive of 2D ordering [17].…”

A study of the dynamics and structure of the dielectric anomaly within the molecular solid TEA(TCNQ)2

“…[12][13][14][15][16][17][18] Even interfaces and defects have been shown to be extremely important within these types of materials and have their own unique electrical conducting behaviour 19,20 that emphasises the low dimensional nature of the molecule and interactions, along with the possible existence of correlated magnetism. 21 One such derived system is TEA(TCNQ) 2 , where TEA = triethylammonium, which was one of the salts listed by Melby et al within their original work. 10 Within the crystal structure of TEA(TCNQ) 2 , 22 a single electron (or electronic charge) is delocalised across two TCNQ molecules, which form a strongly correlated dimer through p-orbital overlap.…”

“…12–18 Even interfaces and defects have been shown to be extremely important within these types of materials and have their own unique electrical conducting behaviour 19,20 that emphasises the low dimensional nature of the molecule and interactions, along with the possible existence of correlated magnetism. 21…”