Tunneling magnetoresistance (TMR) 1,2 via oxides or molecules includes fruitful physics, such as spin filtering 3 and hybridized interface states 4 , in addition to various practical applications using large TMR ratio at room temperature 5 . Then, a larger TMR effect with a new fundamental physics is awaited because further progress on spintronics can be realized. Here we report a discovery of a gigantic TMR ratio of 1,400,000% in a C 60 -Co nanocomposite spin device. The observed effect is induced by a combination of a Coulomb blockade effect and a novel magnetic switching effect. Theoretical investigation reveals that an electric field and a magnetic field control the magnetization and the electronic charging state, respectively, of the Co nanoparticles as in physics of multiferroics.Molecular tunnel barriers were originally intended as a simple replacement of insulating barriers such as AlO or MgO, several unique features were observed in both stacked TMR devices and nano-composite (granular) devices. For example, recent studies demonstrated (1) a very large TMR at low temperatures 4 and spin-dependent tunneling transport at room temperature 6,7 , (2) the existence of a higher-order (~5 th ) co-tunneling effect 8 , and (3) an enhancement of the spin polarization of ferromagnets at the interface between the ferromagnets and molecules 9,10 . Therefore, it is now recognized that molecular TMR involves novel physical aspects which have not been observed in metallic or inorganic spintronics. Among these aspects, the large magnetoresistance (MR) ratio of 300% at 2 K observed by Barraud and co-workers 4 represents a new frontier in molecular spintronics, because the origin of this large MR was clarified, enabling new options in device design through the incorporation of molecules. However, stronger effects and/or novel physical aspects are in strong demand for further progress of spintronics including molecular spintronics. Here, we report on huge MR of 1,400,000% appeared in a C 60 -Co nanocomposite spin device, in which ferromagnetic Co nanoparticles were uniformly dispersed in a molecular matrix and the C 60 behaved as a tunneling barrier 6-11 . A theoretical modeling, calculations and supporting experiments manifest its physics to be unprecedented multiferroic-like behavior of the Co nanoparticles. Figure 1a shows a schematic of the device structure, in which the gap length, L, was varied from 1.5 to 15 µm (see the Methods section). The compositional ratio of C 60 :Co was estimated to be ~ 9:1 according to the co-evaporation rates. As shown in Fig. 1b, the Co nanoparticles were roughly spherical and uniformly dispersed in the C 60 matrix, and their mean diameter was estimated to be 2.5 ± 0.4 nm on the basis of transmission electron microscopy (TEM) observations. It was also clarified that Co-nanoparticles and C 60 matrix were packed without any visible defects, suggesting the samples were free from any possible magnetostriction or Co-particle motion by bias voltageWe define the magnetic anisotropy energy K per th...
We investigated the magnetic properties of Co2MnSn Heusler alloy films, which were grown by alternate deposition of monoatomic Co, sub-atomic Mn, and sub-atomic Sn layers with electron-beam evaporation, by means of SQUID magnetometory and 119 Sn Mössbauer spectroscopy. The Mössbauer spectra sensitively showed that the local magnetism at the Sn sites in the Co2MnSn films depends on the substrate temperature. We also measured the tunnel magnetoresistance of the magnetic tunnel junctions with a Co2MnSn/MgO/Co2MnSn structure. The magnetoresistance of the junction where the magnetic circumstances at the Sn sites are relatively uniform is measured to be 2 % at 5 K at the present stage.
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