Magnetic properties and phase transitions in (CH3NH 2)K3C60 fulleride: An 1H and 2H NMR spectroscopic study

Denis Arčon, Alexey Y. Ganin, Yasuhiro Takabayashi, Matthew J. Rosseinsky, Kosmas Prassides

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8 Citations (Scopus)

Abstract

The hyperexpanded (CH3NH2)K3C60 fulleride and its perdeuterated analogue were investigated by 1H and 2H NMR spectroscopy between room temperature and 4 K. Two phase transitions at TS = 220 K and TN = 11 K clearly were detected in the temperature dependence of the NMR line shapes, the spectral first (M1 and second (M2) moments, and the spin lattice relaxation times, T1. From 2H NMR line shape analysis, we found that the structural phase transition at TS was driven by the freezing out of the discrete Markovian-type jump motion of the entire K +-ND2CD3 unit that is characterized by an activation energy, Ea = 236(51) meV. Below TS, a sudden change in the temperature dependence of M1 suggests the appearance of a small but nonzero spin density on the K+-NH2CH 3 unit. This could influence the electronic properties of the fulleride phase by modulating the strength of the exchange interactions between C603- anions and controlling the width, W, of the t 1u-derived band. The 1H NMR spectra below TN show significant line broadening consistent with the onset of long-range antiferromagnetic order. 1H NMR line shape calculations revealed the adoption of a type II magnetic structure with an ordering vector, q→II = (1/2, 1/2, 1/2) and individual C60 3- magnetic moments of magnitude (∼0.7 μB) aligned along the crystallographic a-axis.

Original languageEnglish
Pages (from-to)4391-4397
Number of pages7
JournalChemistry of Materials
Volume20
Issue number13
DOIs
Publication statusPublished - 2008 Jul 8

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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