Ligand-based transport resonances of single-molecule magnet spin filters: Suppression of the Coulomb blockade and determination of the orientation of the magnetic easy axis

We investigate single molecule magnet transistors (SMMTs) with ligands that support transport resonances. We find the lowest unoccupied molecular orbitals of Mn12-benzoate SMMs (with and without thiol or methyl-sulfide termination) to be on ligands, the highest occupied molecular orbitals being on the Mn12 magnetic core. We predict gate controlled switching between Coulomb blockade and coherent resonant tunneling in SMMTs based on such SMMs, strong spin filtering by the SMM in both transport regimes, and that if such switching is observed then the magnetic easy axis of the SMM is parallel to the direction of the current through the SMM.Comment: 5 pages, 3 figure

Angular Forces Around Transition Metals in Biomolecules

Quantum-mechanical analysis based on an exact sum rule is used to extract an semiclassical angle-dependent energy function for transition metal ions in biomolecules. The angular dependence is simple but different from existing classical potentials. Comparison of predicted energies with a computer-generated database shows that the semiclassical energy function is remarkably accurate, and that its angular dependence is optimal.Comment: Tex file plus 4 postscript figure

Synthesis, Characterization and Magnetic Susceptibility of the Heavy Fermion Transition Metal Oxide LiV_{2}O_{4}

The preparative method, characterization and magnetic susceptibility \chi measurements versus temperature T of the heavy fermion transition metal oxide LiV_{2}O_{4} are reported in detail. The intrinsic \chi(T) shows a nearly T-independent behavior below ~ 30 K with a shallow broad maximum at about 16 K, whereas Curie-Weiss-like behavior is observed above 50-100 K. Field-cooled and zero-field-cooled magnetization M measurements in applied magnetic fields H = 10 to 100 G from 1.8 to 50 K showed no evidence for spin-glass ordering. Crystalline electric field theory for an assumed cubic V point group symmetry is found insufficient to describe the observed temperature variation of the effective magnetic moment. The Kondo and Coqblin-Schrieffer models do not describe the magnitude and T dependence of \chi with realistic parameters. In the high T range, fits of \chi(T) by the predictions of high temperature series expansion calculations provide estimates of the V-V antiferromagnetic exchange coupling constant J/k_{B} ~ 20 K, g-factor g ~ 2 and the T-independent susceptibility. Other possible models to describe the \chi(T) are discussed. The paramagnetic impurities in the samples were characterized using isothermal M(H) measurements with 0 < H <= 5.5 Tesla at 2 to 6 K. These impurities are inferred to have spin S_{imp} ~ 3/2 to 4, g_{imp} ~ 2 and molar concentrations of 0.01 to 0.8 %, depending on the sample.Comment: 19 typeset RevTeX pages, 16 eps figures included, uses epsf; to be published in Phys. Rev.

Quasi-one-dimensional antiferromagnetism and multiferroicity in CuCrO4_4

The bulk magnetic properties of the new quasi-one-dimensional Heisenberg antiferromagnet, CuCrO$_4$, were characterized by magnetic susceptibility, heat capacity, optical spectroscopy, EPR and dielectric capacitance measurements and density functional evaluations of the intra- and interchain spin exchange interactions. We found type-II multiferroicity below the N\'{e}el temperature of 8.2(5) K, arising from competing antiferromagnetic nearest-neighbor ($J_{\rm nn}$) and next-nearest-neighbor ($J_{\rm nnn}$) intra-chain spin exchange interactions. Experimental and theoretical results indicate that the ratio $J_{\rm nn}/J_{\rm nnn}$ is close to 2, putting CuCrO$_4$ in the vicinity of the Majumdar-Ghosh point.Comment: 9 pages, 8 figures, submitted to PR