Muons and magnets

Abstract:

A tetragonal polymorph of [Ni(HF(2))(pyz)(2)]PF(6) (designated β) is isomorphic to its SbF(6)-congener at 295 K and features linear Ni-FHF-Ni pillars. Enhancements in the spin exchange (J(FHF) = 7.7 K), Néel temperature (T(N) = 7 K), and critical field (B(c) = 24 T) were found relative to monoclinic α-PF(6). DFT reveals that the HF(2)(-) bridges are significantly better mediators of magnetic exchange than pyz (J(pyz)), where J(FHF) ≈ 3J(pyz), thus leading to quasi-1D behavior. Spin density resides on all atoms of the HF(2)(-) bridge whereas N-donor atoms of the pyz ring bear most of the density.

Abstract:

We report the results of muon-spin relaxation measurements on the low-dimensional antiferromagnet Rb 4Cu(MoO 4) 3. No long-range magnetic order is observed down to 50 mK implying a ratio T N/J<0.005 (where J is the principal exchange strength along the spin chains) and an effective ratio of interchain to intrachain exchange of |J ⊥/J|<2×10 -3, making the material an excellent realization of a one-dimensional quantum Heisenberg antiferromagnet. We probe the persistent spin excitations at low temperatures and find that ballistic spin transport dominates the excitations detected below 0.3 K. © 2012 American Physical Society.

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.