Muons and magnets

Abstract:

Rare-earth-metal (M = Nd, Gd and Dy) complexes of the organic monoradicals, 15-crown-5-phenyl nitronyl nitroxide 1 and 15-crown-5- or 18-crown-6-phenyl iminonitroxide 2, were synthesized. We present here magnetic properties of the metal-free radicals and the metal complexes of these organic monoradicals studied using SQUID megnetometry. Almost of all the rare-earth-metal complexes show two-sublattice behavior in a wide range of antiferromagnetic (AFM) intrasublattice and ferromagnetic (FM) intersublattice interactions, Γ and λ, with |CΓ | and |Cλ | ≅ 10 to 100 K (C is the Curie constant) over the temperature range between 1.8 and 300 K, while the metal-free radicals exhibit only weak AFM intermolecular interactions, less than the Weiss constant θ = -1 K. The magnitude of interactions observed in the metal complexes of each radical increase in order from Gd to Dy to Nd complexes. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

An analysis is presented of the behavior of muons in the low-temperature state in spin ice. It is shown in detail how the behavior observed in some previous muon experiments on spin ice in a weak transverse field may result from the macroscopic stray field of magnetized spin ice. A model is presented which allows these macroscopic field effects to be simulated and the results agree with experiment. The persistent spin dynamics at low temperature originate from the sample and could be a muon-induced implantation effect that is operative in out-of-equilibrium systems with long relaxation times.