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The fullerene C60, C70, and C84 molecules, that are composed of ∼99% naturally abundant 12C having spinless nuclei, are considered to have miniature hyperfine interaction and also weak intrinsic spin-orbit coupling (SOC) due to the light carbon atoms. However, it has been theoretically predicted that the curvature of the fullerene molecules may increase the SOC due to the induced hybridization of the π and σ electrons on the carbon atoms that reside on the fullerene molecule surface. In this work, we have measured the spin diffusion length in films of C60, C70, and C84 in NiFe/fullerene/Pt trilayer devices, where pure spin current is injected into the fullerene film at the NiFe/fullerene interface via spin pumping induced by microwave absorption at ferromagnet resonance conditions, and subsequently detected at the fullerene/Pt interface as electrical current via the inverse spin-Hall effect. The obtained spin diffusion lengths in the fullerene films are of the order of 10 nm and increase from C60 to C84 in which the fullerene molecule’s curvature decreases; this finding validates the existence of curvature-induced SOC in the fullerenes. Our results deepen the understanding of spin transport in fullerene films and may benefit the design of molecular spintronic devices.

The training effect for exchange bias in field-cooled Co/CoO bilayers films is investigated. Previous experiments on the same system have shown that, starting from the ascending branch of the first hysteresis loop, coherent magnetization rotation is the dominant reversal mechanism. This is confirmed by the performed numerical simulations, which also indicate that the training is predominantly caused by changes of the rotatable anisotropy parameters of uncompensated spins at the Co/CoO interface. Moreover, in contrast with what is commonly assumed, the exchange coupling between the rotatable spins and the ferromagnetic layer is stronger than the coupling between the ferromagnet and the spins responsible for the bias. Thus, uncompensated spins strongly coupled to the ferromagnet contribute to the coercivity rather than to the bias, whatever the strength of their magnetic anisotropy. © 2014 AIP Publishing LLC. ispartof: JOURNAL OF APPLIED PHYSICS vol:115 issue:24 pages:1-6 status: published

The magnetization reversal of perpendicular exchange biased [Co/Pt]/Co60Fe40/IrMn and [Co/Pt]/Co/IrMn multilayers was investigated by time-resolved surface magneto-optical Kerr effect and Kerr microscopy. Compared with the nearly symmetric reversal of the [Co/Pt]/Co/IrMn with a smaller exchange bias field, significantly asymmetric domain evolution in the [Co/Pt]/Co60Fe40/IrMn with a larger exchange bias field was directly observed by Kerr microscopy. The asymmetric magnetization reversal is discussed in terms of the average thermally activated energy barriers as well as the dispersions of the barriers. The substitution of the interfacial Co60Fe40 layer for Co layer results in an enhancement of the interfacial exchange coupling eint and absolute dispersion of interfacial exchange coupling, σeint, and consequently increases the exchange bias field and reversal asymmetry.

We represent a report on the growth and structure of Cu capping layer on ultrathin Fe films on Si (111) substrate as well as its effect on magnetic anisotropy. Cu grows as forming triangular-shaped pyramids with nano-facets and in epitaxial mode with Kurdjumov-Sachs orientation. Spin reorientation transition (SRT) from out-of-plane to in-plane of Fe films is induced by Cu capping, which is believed to be mainly affected by strain change in Fe films. Based on strain relief mechanism, rapid decrease in Cu critical thickness to induce SRT with increasing Fe underlayer thickness can be interpreted quite well.

Magnetic behaviors of Fe nanowires grown on 4° miscut Si(111) substrate with Pb buffer layers have been investigated by means of Monte Carlo method. A simple model is constructed, in which the Fe chains are assumed to be assemblies of single domain Fe nanoclusters with magnetostatic energy and exchange coupling energy. The coverage dependence of the magnetic ordering temperature TC of the system is discussed. By accurately calculating the magnetostatic energy of the Fe chains, the simulated results are in agreement with the experimental ones measured by in situ surface magneto-optical Kerr effect. In addition to the magnetostatic energy, the exchange coupling between the overlapping islands is also responsible for the ferromagnetic ordering of high coverage Fe chains at room temperature. Our model was able to predict the essential features of the system.