Electron paramagnetic resonance linewidth studies in AMnX 3 type compounds

Abstract

Electron paramagnetic resonance (EPR) linewidth studies have been performed in TlMnCl 3 and TlMnF 3 which order in an antiferromagnetic structure at 118 and 85 K respectively. In both cases, a single exchange narrowed line is observed with linewidth ΔH exp much larger than that predicted by the simple theory of exchange narrowing developed by Van Vleck. Various line profiles—truncated Lorentzian, Gaussian-Lorentzian, truncated double Lorentzian, and Gaussian double Lorentzian—have been considered to account for this observation. The EPR linewidth has been measured as a function of temperature between 300 K and the ordering temperature T N. Critical narrowing of the EPR line is observed for temperatures T lying in the interval T N + 20> T > T N. This suggests that long-range order starts building up even above the ordering temperature T N.