A Mössbauer Study of Iron Impurities in the Linear Antiferromagnet TMMC

Abstract

Mössbauer measurements of TMMC (⁵⁷Co) have been carried out. Two different charged states, Fe²⁺ and Fe³⁺, of iron were observed.
The Mössbauer spectrum of ⁵⁷Fe in TMMC has been measured down to 0.3 K. Below the three dimensional transition point no magnetic h. f. s. was observed at the Fe²⁺ site. It is explained by cancellation of the Fermi contact field by the orbital and dipolar internal field. From the analysis of the Q. S. vs T of Fe²⁺ in TMMC, the following crystal field parameters were obtained: Δ=100 cm⁻¹±15, λ=75±5 cm⁻¹. Below 4.2 K it is necessary to introduce the exchange interaction between the Fe²⁺ and Mn²⁺ ions along the chain. A value of |J|=8±1 cm⁻¹ was obtained within the molecular field approximation.
The following Mössbauer parameters were obtained for the Fe²⁺ and Fe³⁺ ions in TMMC Fe²⁺:
Fe²⁺ IS=1.36±0.05 mm/sec., θ_D=106±20 K,
Fe³⁺ IS=0.58±0.05 mm/sec., θ_D=102±25 K.