Influence of HF2- geometry on magnetic interactions elucidated from polymorphs of the metal-organic framework [Ni(HF2)(pyz)2]PF6 (pyz = pyrazine).

Dalton Trans 41 (2012) 7235-7243

JL Manson, KE Carreiro, SH Lapidus, PW Stephens, PA Goddard, RE Del Sesto, J Bendix, S Ghannadzadeh, I Franke, J Singleton, T Lancaster, JS Möller, PJ Baker, FL Pratt, SJ Blundell, J Kang, C Lee, M-H Whangbo

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.

Monopoles, magnetricity, and the stray field from spin ice.

Phys Rev Lett 108 (2012) 147601-

SJ Blundell

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.

Recent Topics of Organic Superconductors


A Ardavan, S Brown, S Kagoshima, K Kanoda, K Kuroki, H Mori, M Ogata, S Uji, J Wosnitza

[Ni(HF2)(3-Clpy)4]BF4 (py = pyridine): evidence for spin exchange along strongly distorted F···H···F- bridges in a one-dimensional polymeric chain.

Inorg Chem 51 (2012) 7520-7528

JL Manson, AG Baldwin, BL Scott, J Bendix, RE Del Sesto, PA Goddard, Y Kohama, HE Tran, S Ghannadzadeh, J Singleton, T Lancaster, JS Möller, SJ Blundell, FL Pratt, VS Zapf, J Kang, C Lee, M-H Whangbo, C Baines

[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.

Proximal magnetometry of monolayers of magnetic moments


Z Salman, SJ Blundell

Chemistry at the nanoscale: synthesis of an N@C60-N@C60 endohedral fullerene dimer.

Angew Chem Int Ed Engl 51 (2012) 3587-3590

BJ Farrington, M Jevric, GA Rance, A Ardavan, AN Khlobystov, GAD Briggs, K Porfyrakis

Persistent dynamics in the S=1/2 quasi-one-dimensional chain compound Rb 4Cu(MoO 4) 3 probed with muon-spin relaxation

Physical Review B - Condensed Matter and Materials Physics 85 (2012)

T Lancaster, PJ Baker, FL Pratt, SJ Blundell, W Hayes, D Prabhakaran

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.

Gradual destruction of magnetism in the superconducting family NaFe1-xCoxAs

PHYSICAL REVIEW B 85 (2012) ARTN 054503

JD Wright, T Lancaster, I Franke, AJ Steele, JS Moeller, MJ Pitcher, AJ Corkett, DR Parker, DG Free, FL Pratt, PJ Baker, SJ Clarke, SJ Blundell

Magnetism in crown-ether-substituted nitronyl nitroxide derivatives and their metal complexes

Physica Status Solidi (C) Current Topics in Solid State Physics 9 (2012) 1205-1207

T Sugano, SJ Blundell, W Hayes, H Tajima, H Mori

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.

Importance of halogen ··· halogen contacts for the structural and magnetic properties of CuX <inf>2</inf>(pyrazine-N,N'-dioxide) (H <inf>2</inf>O) <inf>2</inf> (X = Cl and Br)

Inorganic Chemistry 51 (2012) 2121-2129

JA Schlueter, H Park, GJ Halder, WR Armand, C Dunmars, KW Chapman, JL Manson, J Singleton, R McDonald, A Plonczak, J Kang, C Lee, MH Whangbo, T Lancaster, AJ Steele, I Franke, JD Wright, SJ Blundell, FL Pratt, J De George, MM Turnbull, CP Landee

The structural and magnetic properties of the newly crystallized CuX 2(pyzO)(H 2O) 2 (X = Cl, Br; pyzO = pyrazine-N,N'-dioxide) coordination polymers are reported. These isostructural compounds crystallize in the monoclinic space group C2/c with, at 150 K, a = 17.0515(7) Å, b = 5.5560(2) Å, c = 10.4254(5) Å, β = 115.400(2)°, and V = 892.21(7) Å 3 for X = Cl and a = 17.3457(8) Å, b = 5.6766(3) Å, c = 10.6979(5) Å, β = 115.593(2)°, and V = 950.01(8) Å 3 for X = Br. Their crystal structure is characterized by one-dimensional chains of Cu 2+ ions linked through bidentate pyzO ligands. These chains are joined together through OH···O hydrogen bonds between the water ligands and pyzO oxygen atoms and Cu-X⋯X-Cu contacts. Bulk magnetic susceptibility measurements at ambient pressure show a broad maximum at 7 (Cl) and 28 K (Br) that is indicative of short-range magnetic correlations. The dominant spin exchange is the Cu-X···X-Cu supersuperexchange because the magnetic orbital of the Cu 2+ ion is contained in the CuX 2(H 2O) 2 plane and the X··· X contact distances are short. The magnetic data were fitted to a Heisenberg 1D uniform antiferromagnetic chain model with J 1D/k B = -11.1(1) (Cl) and -45.9(1) K (Br). Magnetization saturates at fields of 16.1(3) (Cl) and 66.7(5) T (Br), from which J 1D is determined to be -11.5(2) (Cl) and -46.4(5) K (Br). For the Br analog the pressure dependence of the magnetic susceptibility indicates a gradual increase in the magnitude of J 1D/k B up to -51.2 K at 0.84 GPa, suggesting a shortening of the Br···Br contact distance under pressure. At higher pressure X-ray powder diffraction data indicates a structural phase transition at ∼3.5 GPa. Muon-spin relaxation measurements indicate that CuCl2(pyzO)(H 2O) 2 is magnetically ordered with T N = 1.06(1) K, while the signature for long-range magnetic order in CuBr2(pyzO)(H 2O) 2 was much less definitive down to 0.26 K. The results for the CuX 2(pyzO)(H 2O) 2 complexes are compared to the related CuX 2(pyrazine) materials. © 2012 American Chemical Society.

BF <inf>4</inf> (py = pyridine): Evidence for spin exchange along strongly distorted F⋯H⋯F <sup>-</sup> bridges in a one-dimensional polymeric chain

Inorganic Chemistry 51 (2012) 7520-7528

JL Manson, AG Baldwin, BL Scott, J Bendix, RE Del Sesto, PA Goddard, Y Kohama, HE Tran, S Ghannadzadeh, J Singleton, T Lancaster, JS Möller, SJ Blundell, FL Pratt, VS Zapf, J Kang, C Lee, MH Whangbo, C Baines

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.

Superconductors: What they're good for

New Scientist 212 (2011) 6-7

S Blundell

Already used in applications as diverse as body scanning and discovering the origin of mass, superconductors hold promise for even greater technologies. © 2011 Reed Business Information Ltd, England.

Superconductors: Cold beginnings

New Scientist 212 (2011)

S Blundell

It took more than half a century to figure out how superconductivity might work and how to make it useful. © 2011 Reed Business Information Ltd, England.

Superconductors: Getting warmer

New Scientist 212 (2011) 4-5

S Blundell

What we really want is a superconductor that operates at room temperature. Might one be within our grasp? © 2011 Reed Business Information Ltd, England.

Critical behavior in the inhomogeneous ferromagnet SrFe <inf>0.80</inf>Co<inf>0.20</inf>O<inf>3.0</inf>

Physical Review B - Condensed Matter and Materials Physics 83 (2011)

J Lago, MJ Rosseinsky, SJ Blundell, PD Battle, M Diaz, I Uriarte, T Rojo

A detailed muon spin relaxation (μSR) and magnetization study is presented of the paramagnetic-to-ferromagnetic transition in the compound SrFe0.80Co0.20O3. The critical exponents derived from the static critical analysis are close to the theoretical predictions for the Heisenberg model in three dimensions. However, a small drift toward mean-field values is interpreted as arising from the presence of long-range dipolar interactions between the Fe(IV) centers. The evolution of spin dynamics across the transition determined from the μSR study is consistent with this interpretation. μSR and magnetization data also provide evidence of an inhomogeneous magnetic state both above and below Tc, placing this system in line with other double-exchange materials such as manganites and cobaltites where spontaneous electronic and magnetic phase separation appears conspicuous and explains much of the encountered experimental phenomenology. © 2011 American Physical Society.

Measurement of the internal magnetic field in the correlated iridates Ca4IrO6, Ca5Ir3O12, Sr3Ir2O7 and Sr2IrO4

Physical Review B - Condensed Matter and Materials Physics 83 (2011)

I Franke, PJ Baker, SJ Blundell, T Lancaster, W Hayes, FL Pratt, G Cao

Oxides containing iridium ions display a range of magnetic and conducting properties that depend on the delicate balance between interactions and are controlled, at least in part, by the details of the crystal architecture. We have used muon spin rotation (μSR) to study the local field in four iridium oxides, Ca4IrO6, Ca5Ir3O 12, Sr3Ir2O7, and Sr 2IrO4, which show contrasting behavior. Our μSR data on Ca4IrO6 and Ca5Ir3O12 are consistent with conventional antiferromagnetism where quasistatic magnetic order develops below TN=13.85(6) and 7.84(7) K, respectively. A lower internal field is observed for Ca5Ir3O12, as compared to Ca4IrO6, reflecting the presence of both Ir4+ and Ir5+ ions and resulting in a more magnetically dilute structure. Muon precession is only observed over a restricted range of temperature in Sr3Ir2O7, while the Mott insulator Sr2IrO4 displays more complex behavior, with the μSR signal containing a single, well-resolved precession signal below T N=230 K, which splits into two precession signals at low temperature following a reorientation of the spins in the ordered state. © 2011 American Physical Society.

Coherent state transfer between an electron and nuclear spin in N15@C <inf>60</inf>

Physical Review Letters 106 (2011)

RM Brown, AM Tyryshkin, K Porfyrakis, EM Gauger, BW Lovett, A Ardavan, SA Lyon, GAD Briggs, JJL Morton

Electron spin qubits in molecular systems offer high reproducibility and the ability to self-assemble into larger architectures. However, interactions between neighboring qubits are "always on," and although the electron spin coherence times can be several hundred microseconds, these are still much shorter than typical times for nuclear spins. Here we implement an electron-nuclear hybrid scheme which uses coherent transfer between electron and nuclear spin degrees of freedom in order to both effectively turn on or off interqubit coupling mediated by dipolar interactions and benefit from the long nuclear spin decoherence times (T2n). We transfer qubit states between the electron and N15 nuclear spin in N15@C60 with a two-way process fidelity of 88%, using a series of tuned microwave and radio frequency pulses and measure a nuclear spin coherence lifetime of over 100 ms. © 2011 American Physical Society.

[Cu(HF(2) )(2) (pyrazine)](n) : A Rectangular Antiferromagnetic Lattice with a Spin Exchange Path Made Up of Two Different FHF(-) Bridges.

Angew Chem Int Ed Engl (2011)

JL Manson, ML Warter, JA Schlueter, T Lancaster, AJ Steele, SJ Blundell, FL Pratt, J Singleton, RD McDonald, C Lee, MH Whangbo, A Plonczak

Magnetic phase transitions in transition-metal complexes with triazole derivatives

Polyhedron 30 (2011) 3202-3205

T Sugano, M Kurmoo, SJ Blundell, W Hayes, S Vilminot

Three divalent transition-metal (Co, Ni and Cu) complexes with the organic anion, 1,2,4-triazolato (tr), as a ligand molecule were prepared by means of hydrothermal syntheses and their magnetic properties were investigated by SQUID magnetometry. The Co(tr)2 and Cu(tr)2 complexes exhibit long range ordering below 8 and 30 K, respectively, while the Ni(tr)2 complex does not show any magnetic phase transition down to 1.8 K. The magnetization isotherms of Co(tr)2 and Cu(tr)2 measured at 2.0 K show hysteresis loops with the coercive fields of 0.5 and 4.7 kOe, respectively. At temperatures higher than about 50 K, the temperature dependence of the magnetic susceptibility of Co(tr)2, Ni(tr)2 and Cu(tr)2 follows the Curie-Weiss law with the Curie constants of 2.95, 0.945 and 0.420 emu K mol-1 and the Weiss temperatures of -62, -74 and -97 K, respectively. These results suggest that the magnetically ordered phases observed in Co(tr)2 and Cu(tr)2 at low temperatures come from antiferromagnetic interactions resulting in canted arrangements of magnetic moments of the transition-metal cations. We discuss here the magnetic interactions in these transition-metal complexes by referring the results of the magnetization measurements. © 2011 Elsevier B.V. All rights reserved.

[Cu(HF<inf>2</inf>)<inf>2</inf>(pyz)]<inf>n</inf>: A rectangular antiferromagnetic lattice with a spin exchange path made up of two different FHF<sup>-</sup> bridges

Angewandte Chemie - International Edition 50 (2011) 1573-1576

JL Manson, ML Warter, JA Schlueter, T Lancaster, AJ Steele, SJ Blundell, FL Pratt, J Singleton, RD McDonald, C Lee, MH Whangbo, A Plonczak

The two-dimensional antiferromagnet [Cu(HF2)2(pyz)] n (pyz=pyrazine) has a rectangular lattice (see picture) displaying two types of FHF- bridging modes. The spin exchange through Cu-(FHF)2-Cu is about 90% stronger than through Cu-pyz-Cu, and the 1,1-coordinated FHF-, which is close in nature to F - ⋯ HF, is largely responsible for the exchange. C black, Cu red, F green, H cyan. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.