Spin-filtering effect in the transport through a single-molecule magnet Mn12_{12} bridged between metallic electrodes

Electronic transport through a single-molecule magnet Mn$_{12}$ in a two-terminal set up is calculated using the non-equilibrium Green's function method in conjunction with density-functional theory. A single-molecule magnet Mn$_{12}$ is bridged between Au(111) electrodes via thiol group and alkane chains such that its magnetic easy axis is normal to the transport direction. A computed spin-polarized transmission coefficient in zero-bias reveals that resonant tunneling near the Fermi level occurs through some molecular orbitals of majority spin only. Thus, for low bias voltages, a spin-filtering effect such as only one spin component contributing to the conductance, is expected. This effect would persist even with inclusion of additional electron correlations.Comment: Accepted for publication at J. Appl. Phy

First-principles study of electron transport through the single-molecule magnet Mn12

We examine electron transport through a single-molecule magnet Mn12 bridged between Au electrodes using the first-principles method. We find crucial features which were inaccessible in model Hamiltonian studies: spin filtering and a strong dependence of charge distribution on local environments. The spin filtering remains robust with different molecular geometries and interfaces, and strong electron correlations, while the charge distribution over the Mn12 strongly depends on them. We point out a qualitative difference between locally charged and free-electron charged Mn12

Effects of bonding type and interface geometry on coherent transport through the single-molecule magnet Mn12

We examine theoretically coherent electron transport through the single-molecule magnet Mn$_{12}$, bridged between Au(111) electrodes, using the non-equilibrium Green's function method and the density-functional theory. We analyze the effects of bonding type, molecular orientation, and geometry relaxation on the electronic properties and charge and spin transport across the single-molecule junction. We consider nine interface geometries leading to five bonding mechanisms and two molecular orientations: (i) Au-C bonding, (ii) Au-Au bonding, (iii) Au-S bonding, (iv) Au-H bonding, and (v) physisorption via van der Waals forces. The two molecular orientations of Mn$_{12}$ correspond to the magnetic easy axis of the molecule aligned perpendicular [hereafter denoted as orientation (1)] or parallel [orientation (2)] to the direction of electron transport. We find that the electron transport is carried by the lowest unoccupied molecular orbital (LUMO) level in all the cases that we have simulated. Relaxation of the junction geometries mainly shifts the relevant occupied molecular levels toward the Fermi energy as well as slightly reduces the broadening of the LUMO level. As a result, the current slightly decreases at low bias voltage. Our calculations also show that placing the molecule in the orientation (1) broadens the LUMO level much more than in the orientation (2), due to the internal structure of the Mn$_{12}$. Consequently, junctions with the former orientation yield a higher current than those with the latter. Among all of the bonding types considered, the Au-C bonding gives rise to the highest current (about one order of magnitude higher than the Au-S bonding), for a given distance between the electrodes. The current through the junction with other bonding types decreases in the order of Au-Au, Au-S, and Au-H. Importantly, the spin-filtering effect in all the nine geometries stays robust and their ratios of the majority-spin to the minority-spin transmission coefficients are in the range of 10$^3$ to 10$^8$. The general trend in transport among the different bonding types and molecular orientations obtained from this study may be applied to other single-molecular magnets.Comment: Accepted for publication in Phys. Rev. B

ACUTE EFFECTS OF SMALL CHANGES IN BICYCLE SADDLE HEIGHT ON PEDALLING COORDINATION

The purpose of this study was to analyse the acute effects of small changes in bicycle saddle height on pedalling coordination, using vector coding analysis. Lower extremity kinematic data were collected from ten well-trained cyclists while they pedalled at three different saddle heights in random order: preferred, 2% higher and 2% lower than preferred position. A modified vector coding technique and circular statistics were used to quantify coordination for selected hip-knee, hip-ankle, and knee-ankle joint couplings. The results indicate that modifications in saddle height produced moderate alterations in the frequency of movement patterns, which were not enough to alter the classification of coordination. The small modifications observed were in the direction of increasing the frequency of the proximal coordinative pattern as the saddle height decreased

ACUTE EFFECTS OF SMALL CHANGES IN CRANK LENGTH ON TORQUE WAVEFORM DURING SUBMAXIMAL PEDALLING

The purpose of the present study was to evaluate the acute effects of small changes in crank-arm length and pedalling power on crank torque-angle profile during seated cycling. Twelve amateur cyclists participated and performed 12 sets of 5-min submaximal pedalling on a special cycle ergometer (4 intensities x 3 crank lengths). Principal Component Analysis technique was used to analyse ten crank torque-angle curves of the right leg. A longer crank increased the crank torque of the front leg (30-125º) in order to lift the rear leg (200-320º), contrary to the effect of increasing pedalling power. Furthermore, pedalling with the longest crank required higher torque values after reaching peak torque (110-170º) compared to the shortest ones. In conclusion, contrary to the lore, a longer crank requires a higher mechanical effort compared to a shorter crank for pedalling at the same intensity