Quantum spin dynamics

Abstract:

We report the two-step synthesis of a highly soluble fullerene dimer, both for short reaction times and at the microscale. We apply this reaction scheme to starting materials that contain 15N@C60 and 14N@C60, and we demonstrate how, if applied to highly pure N@C60 in the future, this scheme may be used to produce (14N@C60)2 or (15N@C60)2 dimers in one step, and crucially 14N@C60-15N@C60 dimers in a second step. Such dimers represent isolated electron spin pairs that may be used to demonstrate entanglement between the spins. Additionally, CW EPR spectroscopy of the 15N@C60-C60 dimer in the solid state reveals permanent zero-field splitting (D = 14.6 MHz and E = 0.56 MHz). © 2013 Royal Society of Chemistry.

Abstract:

Solid state techniques involving pressure and temperature have been used to synthesize the fluoride member of the CuX(2)(pyrazine) (X = F, Cl, Br) family of coordination polymers that cannot be crystallized by solution methods. CuF(2)(pyrazine) exhibits unique trans doubly-bridged Cu-F(2)-Cu chains that provide an opportunity to quantify magnetic superexchange in an isostructural Cu-X(2)-Cu series.

Abstract:

This paper reports the experimental and theoretical investigations of two trigonal bipyramidal Ni(II) complexes, [Ni(Me(6)tren)Cl](ClO(4)) (1) and [Ni(Me(6)tren)Br](Br) (2). High-field, high-frequency electron paramagnetic resonance spectroscopy performed on a single crystal of 1 shows a giant uniaxial magnetic anisotropy with an experimental D(expt) value (energy difference between the M(s) = ± 1 and M(s) = 0 components of the ground spin state S = 1) estimated to be between -120 and -180 cm(-1). The theoretical study shows that, for an ideally trigonal Ni(II) complex, the orbital degeneracy leads to a first-order spin-orbit coupling that results in a splitting of the M(s) = ± 1 and M(s) = 0 components of approximately -600 cm(-1). Despite the Jahn-Teller distortion that removes the ground term degeneracy and reduces the effects of the first-order spin-orbit interaction, the D value remains very large. A good agreement between theoretical and experimental results (theoretical D(theor) between -100 and -200 cm(-1)) is obtained.

Abstract:

High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide exhibit a simple, almost axial anisotropy and phase coherence times of the order of a millisecond at low temperatures. The anisotropy energy is tunable using an externally applied electric field. This can be used to control electrically the phase of spin superpositions and to drive spin transitions with resonant microwave electric fields. © 2013 American Physical Society.

Abstract:

High-frequency Electron Paramagnetic Resonance (HFEPR) measurements have been performed on both a single-crystal and powder samples of a weakly coupled antiferromagnetic dinuclear [Mn(III)](2) molecular magnet, [Mn(III)(2)L(2)(py)(4)], where L is the trianion of 3-(3-oxo-3-phenylpropionyl)-5-methylsalicylic acid, and py is pyridine. The experimental results were analyzed on the basis of a multispin Hamiltonian using both a perturbative approach and numerical simulations. It is found that the single-crystal HFEPR results provide a direct and simple means of determining both the axial anisotropy of the individual Mn(III) ions and the isotropic exchange coupling between them. Previously unpublished low-temperature magnetization data are then simulated using the same model Hamiltonian, yielding excellent agreement. This work highlights the limitations of widely used protocols for analyzing magnetic and powder EPR data obtained for multinuclear molecular magnets in which the exchange and single-ion anisotropies are comparable, thus emphasizing the value of single-crystal, multifrequency EPR measurements.