Anomalous magnetic exchange in a dimerized quantum magnet composed of unlike spin species

PHYSICAL REVIEW B 104:21 (2021) ARTN 214435

Authors:

SPM Curley, BM Huddart, D Kamenskyi, MJ Coak, RC Williams, S Ghannadzadeh, A Schneider, S Okubo, T Sakurai, H Ohta, JP Tidey, D Graf, SJ Clark, SJ Blundell, FL Pratt, MTF Telling, T Lancaster, JL Manson, PA Goddard

Intrinsic Nature of Spontaneous Magnetic Fields in Superconductors with Time-Reversal Symmetry Breaking

PHYSICAL REVIEW LETTERS 127:23 (2021) ARTN 237002

Authors:

BM Huddart, IJ Onuorah, MM Isah, P Bonfa, SJ Blundell, SJ Clark, R De Renzi, T Lancaster

Neutron Studies of a High Spin Fe-19 Molecular Nanodisc

MAGNETOCHEMISTRY 7:6 (2021) ARTN 74

Authors:

Francis L Pratt, Tatiana Guidi, Pascal Manuel, Christopher E Anson, Jinkui Tang, Stephen J Blundell, Annie K Powell

Abstract:

The molecular cluster system [Fe19 (metheidi)10 (OH)14O6 (H2O)12 ]NO3·24H2O, abbrevi-ated as Fe19, contains nineteen Fe(III) ions arranged in a disc-like structure with the total spin S = 35/2. For the first order, it behaves magnetically as a single molecule magnet with a 16 K anisotropy barrier. The high spin value enhances weak intermolecular interactions for both dipolar and superexchange mechanisms and an eventual transition to antiferromagnetic order occurs at 1.2 K. We used neutron diffraction to determine both the mode of ordering and the easy spin axis. The observed ordering was not consistent with a purely dipolar driven order, indicating a significant contribution from intermolecular superexchange. The easy axis is close to the molecular Fe1–Fe10 axis. Inelastic neutron scattering was used to follow the magnetic order parameter and to measure the magnetic excitations. Direct transitions to at least three excited states were found in the 2 to 3 meV region. Measurements below 0.2 meV revealed two low energy excited states, which were assigned to S = 39/2 and S = 31/2 spin states with respective excitation gaps of 1.5 and 3 K. Exchange interactions operating over distances of order 10 Å were determined to be on the order of 5 mK and were eight-times stronger than the dipolar coupling.

The Internal Field in a Ferromagnetic Crystal with Chiral Molecular Packing of Achiral Organic Radicals

MAGNETOCHEMISTRY 7:5 (2021) ARTN 71

Authors:

Stephen J Blundell, Tom Lancaster, Peter J Baker, Francis L Pratt, Daisuke Shiomi, Kazunobu Sato, Takeji Takui

Abstract:

The achiral organic radical dinitrophenyl nitronyl nitroxide crystallizes in two enan-tiomorphs, both being chiral tetragonal space groups that are mirror images of each other. Muon-spin rotation experiments have been performed to study the magnetic properties of these crystals and demonstrate that long-range magnetic order is established below a temperature of 1.10(1) K. Two oscil-latory components are detected in the muon data, which show two different temperature dependences.

Magnetic and Structural Properties of Organic Radicals Based on Thienyl- and Furyl-Substituted Nitronyl Nitroxide

MAGNETOCHEMISTRY 7:5 (2021) ARTN 62

Authors:

Tadashi Sugano, Stephen J Blundell, William Hayes, Hatsumi Mori

Abstract:

Magnetic properties of organic radicals based on thienyl-and furyl-substituted nitronyl nitroxide (NN) and iminonitroxide (IN) were investigated by measuring the temperature dependence of the magnetization. The magnetic behavior of 2-benzo[b]thienyl NN (2-BTHNN) is interpreted in terms of the two-magnetic-dimer model, in which one dimer exhibits ferromagnetic (FM) intermolecular interaction and the other dimer shows antiferromagnetic (AFM) interaction. The existence of two dimers in 2-BTHNN is supported by crystal structure analysis. The magnetic behaviors of 2-bithienyl NN, 4-(2′-thienyl)phenyl NN (2-THPNN), 2-and 3-furyl NN, 2-benzo[b]furyl NN, and 3-benzo[b]thienyl IN are also reported. The one-dimensional alternating AFM nature observed in 2-THPNN is consistent with its crystal structure.