Professor Stephen Blundell

Abstract:

The series SrFe 1-xCo xO 3 evolves from spiral antiferromagnetic order to long-range ferromagnetism on increasing Co doping. In the Fe-rich region below the onset of ferromagnetism (x ≤ 0.20), there exists a number of disordered magnetic ground states. Here we present a detailed study of the composition SrFe 0.90Co 0.10O 3, which we find to display quasicanonical spin-glass behavior. The analysis of its freezing transition by means of muon spin relaxation (μSR) spectroscopy and ac and dc susceptibility suggests that the system constitutes a new experimental realization of the three-dimensional Heisenberg spin-glass model with weak random anisotropy. The derived critical exponents are consistent with predictions by Kawamura's chiral driven freezing scenario with a bimodal exchange distribution. © 2012 American Physical Society.

Abstract:

Figure Persented: [Ni(HF 2)(3-Clpy) 4]BF 4 (py = pyridine) is a simple one-dimensional (1D) coordination polymer composed of compressed NiN 4F 2 octahedra that form chains with bridging HF 2- ligands. In spite of significant distortion of the HF 2- bridge, a quasi-1D antiferromagnetic (AFM) behavior was observed with J FHF = 4.86 K. © 2012 American Chemical Society.

Abstract:

[Ni(HF(2))(3-Clpy)(4)]BF(4) (py = pyridine) is a simple one-dimensional (1D) coordination polymer composed of compressed NiN(4)F(2) octahedra that form chains with bridging HF(2)(-) ligands. In spite of significant distortion of the HF(2)(-) bridge, a quasi-1D antiferromagnetic (AFM) behavior was observed with J(FHF) = 4.86 K.

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.